Instrumentation and Monitors

Normal RVDP

0-8 mm Hg

VP sevo

160

mL vapor per mL liquid Sevoflurane at 20C

182

mL vapor per mL liquid Isoflurane at 20C

195

mL vapor per mL liquid Enflurane at 20C

196

Describe the method for PA catheter insertion

1st check balloon, flush all three ports and connect distal port to transducer At ~15 cm distal tip should enter R atrium Inflate ballon (usually ~1.5 ml) Advance into RV SEE INC SBP Advance into PA SEE INC DBP

Allowable ppm halogenated agents without N2O

2 ppm

Peripheral nerve stimulator Twitch length

200 msec

mL vapor per mL liquid Desflurane at 20C

207

mL vapor per mL liquid Halothane at 20C

226

VP iso

240

Vapor pressure halothane

243

Allowable ppm N2O

25 ppm

The O2 pressure-sensor shutoff valve requires what O2 pressure to remain open and allow N2O to flow into the N2O rotameter?

~30psi

How long would a vaporizer (filled with 150 mL volatile) deliver 2% isoflurane if total flow is set at 4.0 L/min?

~6 hours Two percent of 4 L/min will be 80 mL of isoflurane per minute Given that 1 mL of isoflurane yields 195 mL of anesthetic vapor and by applying the calculation: (195 mL vapor/1 mL liquid isoflurane) x (150 mL isoflurane liquid) = 29,250 mL isoflurane vapor, it follows that (29,250 mL/ 80 ml/min= 365 min) 365 minutes is around 6 hours

EKG low frequency filters

Help minimize distortion from patient movement such as produced by patient breathing

Which ECG clues suggest that a patient may have left ventricular hypertrophy?

High QRS voltage is the hallmark of LVH, although many young patients have high QRS voltage without real LVH. Other associated hints (albeit nonspecific) are left axis deviation, left atrial enlargement, widening of QRS and strain (associated with ST-T abnormalities) Patients with LBBB cannot be diagnosed with LVH from the ECG but it is important to remember that many patients with LBBB may actually have LVH.

A resident notices an increasing discrepancy between the PaCO2 and the ETCO2. Factors that increase this difference include all of the following except: mismatch of ventilation and perfusion wheezing high fresh gas flow rates high cardiac output

High cardiac output The difference between arterial and measured ETCO2 will be increased by ventilation-perfusion mismatch (e.g emboli, decreased CO), prolonged expiratory phase (wheezing) and high fresh gas flow rates that dilute expired CO2.

Surgical diathermy

High frequency alternating current to cut/cauterize blood vessels Electro-surgical units (ESUs) generate high frequency current; tip of small electrode-->through patient-->out large electrode (dispersion pad) Malfunction of dispersion pad--inadequate contact/conducting get disconnect--current will exit pt through alternate path (EKG pads, OR table) and may burn the pt Bipolar electrodes limit current propagation to a few mm ESU may interfere with pacemaker and ECG recordings

How does high oxygen content help with decreasing spread of infection?

High oxygen content in any situation leads to free radicals which are bacteriocidal No change in pt airway infection outcomes are noted when using disposable vs reusable anesthesia circuits and volatiles do not inhibit or kill bacterial growth

PIP

Highest pressure during inspiration (dynamic compliance)

Hypothermia is defined as

Hypothermia is defined as a temperature below 36C Anesthetics interfere with normal hypothalamic thermal regulation

What ECG findings suggest hypothyroidism

Low QRS voltage, bradycardia, and QT interval prolongation. There may be associated T wave abnormalities and AV block

What is the pressure of gases lowered to at the second stage O2 pressure regulator?

14-26 psi

Normal PASP

15-25 mm Hg

Normal RVSP

15-25 mm Hg

CVP waveform

+ a wave: this wave is due to increased atrial pressure during right atrial contraction + c wave: this wave is caused by slight elevation of the tricuspid valve into the right atrium during early ventricular contraction. It correlates with the end of the QRS on EKG x descent- probably caused by the downward movement of the ventricle during systolic contraction. Occurs BEFORE T wave + v wave: this wave arises from the pressure produced when the blood filling the right atrium comes up against the closed tricuspid valve. It occurs as the T wave is ending on EKG y descent- this wave is produced by the tricuspid valve opening in diastole with blood flowing to the right ventricle. Occurs before P wave on EKG

The maximum FIO2 that can be delivered via nasal cannula is

0.45 The FIO2 delivered to patients from low-flow systems (nasal prongs) is determined by the size of the O2 reservoir, the O2 flow, and the patient's breathing pattern. As a rule of thumb, assuming a normal breathing pattern, the FIO2 delivered by nasal prongs is ~0.04 L/min increase in O2 flow up to a maximal FIO2 of ~.45 (at an O2 flow of 6 L/min) In general, the larger the patients TV or the faster to respiratory rate, the lower the FIO2 for a given O2 flow

Allowable ppm halogenated agents with N2O

0.5 ppm

What is normal UO?

1-2 ml/kg/hr

What are the 4 components of Mapelson Circuits?

1. Breathing tubes- made of rubber or plastic, connect pt to the mapelson circuit. Large diameter tubing is often used to ensure low resistance 2. Fresh gas inlet- the point of entry of anesthetic gases and oxygen to the Mapelson circuit. The relative position of the fresh gas inlet is a key factor in differentiating the mapelson classification and system performance 3. Reservoir Bag- function as a reservoir of anesthetic gas and a method of generating PPV. Designed to have high compliance 4. Adjustable pressure limiting (APL) valve- an expiratory valve that allows for exit of gases form the circuit. It allows for a variable pressure threshold for venting gases from the circuit. Partial closure of the APL valve limits gas exit, thus permitting PPV during bag compressions

The minimum macroshock current required to elicit ventricular fibrillation is

100 mA Leakage electrical currents less than 1 mA are imperceptible to touch. The minimal ventricular fibrillation threshold of current applied to the skin is about 100 mA. If the current bypasses the high resistance of the skin and is applied directly to the heart via pacemaker, central line, etc (microshock) currents as low as 100 microA (0.1 mA) may be fatal. Because of this the American National Standards Institute has set the maximum leakage of electrical current allowed through electrodes or catheters in contact with the heart at 10 microA

ASA recommendations for the minimum E cylinder O2 pressure?

1000 psi

During the middle of an emergency surgery to treat an aortic dissection the main gas pressure supply alarm starts to sound. At this time you notice the EtCO2 increasing and the patient slowly starts to desaturate. After quickly attempting to diagnose the situation you are faced with you rapidly attach the manual resuscitator to the endotracheal tube and connect the supply tubing to the oxygen E-Cylinder. The surgeon states that he must continue the case. You are able to get a propofol infusion set up and check the tank to estimate how much time you have left running at 15 L/min oxygen flow rate. Assuming the current psig on the oxygen E-cylinder reads 1800, how many minutes do you have left with the tank? Select one: a. 21 minutes b. 39 minutes c. 45 minutes d. 73 minutes e. 89 minutes

39 minutes remain in the tank running at this oxygen flow rate. Use the formula: P1/V1=P2/V2 If P1= 2000 V1=660 L P2 =1800 V2= X, input your numbers to get: 2000/660=1800/X giving you that X=594 L. Running at 15 liters per minute, divide 594 liters left by the 15 liters per minute you are using: 594 L x (min/15 L) = 39.6 minutes remaining, rounded to 39 minutes. Broken down differently: Since pressure and volume in an oxygen gas cylinder are directly proportional, use this equation: P1/V1=P2/V2 Solving for V2 gives the equation: (V1/P1)X P2 = V2 (660 L/2000 psig) X 1800 psig = 594 L Another strategy for finding the remaining volume, is to view the pressure reading as a fraction of full pressure and then multiply that by the full volume to get the fraction of the volume left over. Volume left = 1800 psig/2000 psig X 660 L Volume left = 0.9 X 660 L Volume left = 594 L If the flow is set at 15 L/min, then the time left on the tank is 594 L/(15 L/min) or 39.6 minutes. Always round down in these problems. There are 39 minutes left on the tank. The correct answer is: 39 minutes

TOF with peripheral nerve stimulator

4 successive 200 msec stimuli occurs in 2 seconds Disappearance of 4th twitch 75% block Disappearance of 3rd twitch 80% block Disappearance of 2nd twitch 90% block

What are BIS levels for GA?

40-65

How much does post op shivering increase oxygen requirement?

5-fold

A patient is being ventilated with a traditional anesthesia machine ventilator using the following setting parameters: TV: 500 mL RR: 10/min I:E ratio: 1:3 Oxygen flow: 1 L/min N2O flow: 2 L/min What is the resulting minute ventilation?

5.75 L/min In a typical anesthesia ventilator, during inspiration, the pressure relief valve is closed so that the TV delivered to the patient is the sum of the set TV plus the fresh gas flow that occurs during inspiration. In this case, the total fresh gas flow is 3,000 mL/min or 50 mL/sec With a ventilator rate of 10/min each breath lasts for 6 sec. With an I:E ratio of 1:3, the inspiratory phase lasts for 1.5 sec. Therefore, the set tidal volume is augmented by fresh gas flowing for 1.5 sec, or 75 mL/breath

Tetany and peripheral nerve stimulator

50-100 Hz sustained contraction for 5 sec indicates adequate recovery

A patient is connected to an IV bag with a flow rate of 90 ml/hr. During patient management you notice BP drop so you give 100 mcg of phenylephrine. There is 3 mL of fluid form the port to the IV catheter. How long must you wait for 95% of the phenylephrine to be infused into the patient?

6 minutes are required from administration to wash in as it takes 3 time constants for wash in to occur. A single time constant in this equation is 2 min. This is a time constant equation: The equation to determine time constants is volume/flow Since the volume from the IV port to the catheter is 3 mL that is the volume (numerator) and flow rate 90 ml/hr (denominator) 3/90= 0.033 hour x min (60) to determine a single time constant

PAOP = PCWP

6-12 mm Hg

What are BIS levels for sedation?

65-85

VP des

669

An anesthesia circuit is connected to a circle system and the combined volume of both is 6 L. The fresh gas flow is 3 L/min. After isoflurane 2% is turned on, how long will it take the concentration in the circuit to reach 1.96% isoflurane (i.e 98.1% of the concentration set on the vaporizer?

8 min The time constant of the system is the volume divided by the fresh gas flow, i.e., 6 L/(3 L/min), or two minutes. Since 1-e^(-t/t) = 1 -e^-1= 0.63, after once time constant the isoflurane concentration with be 63% of the value set on the vaporizer. After two time constants, the percentage is 85%, after three time constants , 95%, and after 4 time constants, 98%, and after 5 time constants 99.3%

Normal PADP

8-15 mm Hg

Oxygen Cylinders

99.5% pure E cylinder: 2000 psi, 660 L H cylinder: 6000-9000 L Liquid oxygen tank: below -119C (Gases can be liquified by pressure only if stored below their critical temp) GREEN

A N2O E cylinder pressure gauge reads 600 psi. How many liters are left?

A N2O E cylinder will read 745 psi until there is only 400 L left in the tank 600 psi/745 psi= 0.805 multiply that by 400 L

N2O volume

A full E cylinder of N2O is approximately 8.8 kg; an empty cylinder is approximatley 5.9 kg. Volume remaining (L) = (cylinder weight (g) - 5900 g) x 0.55 L/g Volume remaining = (gauge pressure (psig)/ 745 psig) x 253 L

What flows are needed to provide an FiO2 of 1.0 with a manual bag valve mask resuscitator?

A minimum of 10 L/min is required to provide an FiO2 that will approximate 1.0 with a manual bag valve mask resuscitator

A 34 year old man who weighs 80 kg who has underwent a sigmoid colectomy is prepared for extubation. After reversal, you note that the patient is able to breath 400 mL without ventilator support. Based on his ability to self ventilate at 5 mL/kg only, what percentage of receptors at the neuromuscular junction may still be blocked? Select one: a. 40 % b. 50 % c. 60 % d. 70 % e. 80 %

A patient who is able to spontaneously ventilate a tidal volume of greater than 5 mL/kg still can have 80% of receptors occupied. Other tests should be used to determine if a patient is ready for extubation, as pharyngeal muscles and airway reflexes may still be impaired. Removal of an endotracheal tube in such an impaired patient can result in respiratory failure or aspiration. The correct answer is: 80 %

A closed ventilator pressure relief valve can result in: Select one: a. Barotrauma b. Insidious escape of volatile agents into the operating theater c. Decreased expiratory resistance d. Damage to pipeline regulators e. Deceased ability to expand the lungs

A pressure relief valve is designed to prevent barotrauma from occuring by relieving excess pressure. If there is no mechanism for increased pressures to escape the ventilator circuit, pressure within the system will build up. Short of a failure of the system, pressures will continue to increase until damage is caused to the lungs. Airway pressure monitoring will alert you to any problem of this nature. Unless rupture of a reservoir bag or other circuit failure occurs, ventilated gases will not escape the system. The correct answer is: Barotrauma

The device used to reduce the pressure of a gas from a compressed cylinder to a usable, nearly constant pressure is

A regulator The mechanism to reduce pressure of a gas to a useful pressure is a regulator. A gauge is a device to measure the pressure. The flowmeter is a device to measure the flow being delivered A check valve is a device to allow flow in only one direction

A 42 year old female is administered 40 mg of rocuronium during induction for a shoulder arthroscopy and acromioplasty. Prior to extubation, you perform a train-of-four stimulation test and receive 4 out of 4 twitches (without testing for sustained tetany) and note no fade. What percentage of receptors at the neuromuscular junction may still be blocked? Select one: a. 40 % b. 50 % c. 60 % d. 70 % e. 80 %

A train of four with 4 out of 4 twitches and no fade alone can still have 70% of receptors occupied. Therefore, other tests such as head lift, sustained tetany, and hand grip should be used to increase the margin of safety prior to extubation. Failure to ensure adequate return of neuromuscular function can lead to collapse of weak pharyngeal muscular that can lead to airway obstruction, as well as decreased ability of the patient to ventilate and possible aspiration if airway reflexes have not returned to decent function. The correct answer is: 70 %

The isolated power supply system used in operating rooms requires that

A transformer be connected between electrical equipment in the operating room and the electric power supplied by the utility company In an isolated power supply system, an isolation transformer is connected between the electric power supplied by the utility company and the electrical outlets in the OR. The safety provided by this system depends on the patient and any wires or metallic objects in contact with the patient not being connected to earth ground. Conductive flooring was used in the past to avoid static electricity sparks that could cause fires or explosions in the presence of flammable anesthetics

How does the CVP waveform change with AV dissociation?

A waves will be dramatically increased AKA Cannon A waves as the atrium contracts against closed tricuspid valve

A 42 year old obese male presents for an emergent appendectomy due to perforation. After induction of GA, mask ventilation becomes inadequate and several intubation attempts are unsuccessful as the patient desaturates. A large bore catheter is placed through the cricothyroid membrane and jet ventilation is initiated. Which of the following is MOST TRUE regarding transtracheal jet ventilation? A. A 16 ga or larger catheter should be placed using a Seldinger technique B. A minimum pressure of 35 psi is required for jet ventilation C. Reducing the passive expiration time decreases the risk of developing a pneumothorax D. Transtracheal jet ventilation is considered a non-invasive emergency airway

A. A 16 ga or larger catheter should be placed using a Seldinger technique Transtracheal jet ventilation typically involves placement of a large bore catheter by using a needle to first aspirate air, then passing a specifically-designed guidewire followed by the catheter, in a process known as the Seldinger technique. Transtracheal jet ventilation is a rapid but invasive method for oxygenating a patient in the ASA emergency airway algorithm. Although it can only be used as a temporary airway, the technique is reserved as a "last resort" and can prove to be life-saving. The external tracheal anatomy is clearly identified and sterilized. A 12-16 ga needle with an attached syringe is advanced through the cricothyroid membrane until air is aspirated. Once the syringe is removed, a Teflon-coated kink resistant guidewire is passed using a Seldinger technique along with a large bore catheter. Jet ventilation can then be initiated. It can provide a mx pressure of 55 psi directly from pipeline pressure, but a min of 15 psi is required to drive the ventilatory. Higher pressures are associated with displaced catheters and barotrauma, and therefore a max 35 psi is recommended. Jet ventilation requires passive expiration, as the chest wall begins to collapse and the lungs deflate. This process takes longer than the time for active inspiration, and therefore adequate time for passive expiration must be allocated at the end of each breath. If the passive expiration time is reduced, for example in cases of high respiratory rates, air will remain in the lungs as the next breath is given. This leads to a phenomenon known as air trapping. The volume and pressure within the lungs increase with each breath. as dose the risk of pneumothorax. Therefore, allowing adequate time for passive expiration between breaths is vitally important. Contraindications to transtracheal jet ventilation include trauma and distorted airway anatomy, while relative contraindications include COPD and coagulopathy. Including barotrauma and pneumothorax, adverse complications include damage to the trachea or esophagus, hemorrhage, subcutaneous emphysema, mediastinal emphysema, and possible aspiration.

What distinguishing factor of a bag valve mask (self-reinflating bag) allows it to reinflate? A. A bag inlet valve B. An APL valve C. Fresh gas flow D. Negative pressure via spontaneous ventilation

A. A bag inlet valve A bag inlet valve is a one-way inlet valve that allows air as well as fresh gas to flow into the bag reservoir as it re-expands. There are several kinds of bag valve masks (BVM). Generally, they can be separated into self-reinflating or non-self-reinflating. The most common self-reinflating bag known to anesthesia providers is the modified Mapleson C circuit known by its proprietary name, the Ambu bag. This device features an APL close to the patient. This attaches to a ventilation bag made of plastic with an inherent memory that allows it to reinflate after being squeezed. As the bag re-expands, it draws air from the distal bag inlet valve, which allows it to reinflate with air. This specific component makes the self-reinflating bag ideal for emergency and transport environments as it requires no FGF source. Nevertheless, most modern self-reinflating bags have an inlet fro FGF into an attached reservoir to allow ventilation with near 100% oxygen if available. the alternative to self-reinflating BVM are non-self-reinflating bags. An example of this type of BVM commonly used by anesthesia providers would be the Mapleson F circuit called a Jackson-Rees circuit. This circuit features a FGF inlet proximal to the patient. This is followed by corrugated tubing that leads to the ventilation bag. This ventilation bag is closed distally by an APL valve to allow for controlled ventilation and scavenging. Without the reinflation feature, however, the circuit cannot be used to ventilate the patient without FGF. The soft ventilaiton bag material and the APL make this device especially useful in the spontaneously breathing patient. Answer B: an APL valve is a one-way outlet valve that maintains pressure in the ventilation bag thereby allowing for controlled ventilation and scavenging, but does not play a role in bag reinflation. Answer C: FGF is necessary for non-self-reinflating BVM, but does not distinguish self-reinflating BVM. Answer D: negative pressure does not allow for self-reinflation. It is the bag inlet valve that makes this possible.

Which of the following is MOST TRUE regarding intermittent NIBP? A. As the site of cuff measurement moves more peripherally, the diastolic BP tends to decrease B. Automated sphygmomanometers estimate the SBP at the point of maximal amplitude oscillations C. Every patient receiving anesthesia shall have arterial BP determined and evaluated at least every 3 minutes D. The order of accuracy for automated sphygmomanometers is SBP > MAP > DBP

A. As the site of cuff measurement moves more peripherally, the diastolic BP tends to decrease Pulse pressure increases as the cuff is moved more distally. PP = SBP - DBP. Hence, the SBP increases and the DBP decreases more distally Order of cuff accuracy MAP > SBP > DBP Korotkoff sounds may be heard using auscultation of the brachial artery while deflating the cuff. Appearance of sound = SBP--Disappearance = DBP

Administering 50% nitrous oxide to a patient with a 100 mL pneumothorax will expand the pneumothorax to what volume? Select one: a. 100 mL b. 150 mL c. 175 mL d. 200 mL e. 500 mL

Administering 50% nitrous oxide will expand closed air spaces to double the original volume (in this instance to 200 mL). The amount of nitrous oxide that will diffuse into a closed air space will be that which results in an equal concentration of nitrous oxide to the inspired level. In this case, to get 50% (or half) of the air in the pneumothorax to be nitrous oxide, 100 mL of nitrous oxide will have to diffuse into the area which already contains 100 mL of air. This will result in a gas total of 200 mL. The correct answer is: 200 mL

GA ETT anesthesia is being delivered to a patient with a combination of oxygen, N2O, and isoflurane. As the gas flow throw a bobbin rotameter is increased, which of the following increase? A. Cross sectional orifice area B. Gas density C. Gas viscosity D. Laminar flow

A. Cross sectional orifice area In an anesthesia machine as the flow through a rotameter increases, the cross sectional area of the orifice around the rotameter increases as well. A bobbin rotameter, AKA variable area meter, is used to indicate the current flow rate for a particular gas. Typically this includes oxygen, room air, and N2O. The flowmeter is structured as a tapered cylinder, wider at the top than the bottom. A small ring-shaped gap exists between the rotameter and the surrounding tube, and as the gas flow is increased the bobbin will rise further. Due to the tapered nature of the cylinder, the cross-sectional area will increase as well. The rotameter bobbin will continue to rise until an equilibrium is reached between the weight of the bobbin and the pressure beneath it. The gas flow above the bobbin is highly turbulent, and as with most fluid dynamics, turbulent flow will increase as velocity and flow are increased as well. Each rotameter is calibrated for a particular gas, due to each gas' innate properties such as density and viscosity. These values are not altered by changes in gas flow B&C: density and viscosity are properties of each individual gas, and will not be affected by changes in gas flow D. In a bobbin rotameter, gas flow is generally more laminar below the bobbin and more turbulent above. Regardless, as with most fluid dynamics, it will become more turbulent as flow velocity increases

A pacemaker is placed in a 78 year old man via the axillary vein in the left upper chest. The leads are inserted into which of the following layers of the heart? A. Endocardium B. Epicardium C. Myocardium D. Pericardium

A. Endocardium Permanent pacemaker placement is typically accomplished via a transvenous approach. Pacemaker leads are threaded through the axillary or subclavian vein and then the superior vena cava and into the right atrium, right ventricle, or both chambers. The end of the lead is placed into the endocardium. The generator is implanted subcutaneously in the upper chest. Answer B: Temporary epicardial pacemaker leads can be placed when patients are undergoing concomitant heart surgery. Permanent epicardial lead placement is much less common in adults than transvenous placement but is an option used in pediatric patients.

In a patient receiving general anesthesia, which of the following techniques would MOST reduce heat loss during phase I of hypothermia? A. Forced air warming blanket B. Heated humidification of inspired gases C. Warm water blanket D. Warming of IV fluids

A. Forced air warming blanket Application of a forced-air warming blanket for a half hour prior to surgery is the most effective way to prevent heat loss during the first phase of hypothermia. Following induction of general anesthesia, there is a large shift of body heat form the core to the peripheral tissues, a process known as redistribution. During the first hour of anesthesia, redistribution is responsible for a drop in core body temperature between 1-2 degrees celsius and is labeled phase I of hypothermia. In the OR, this can include radiation (loss of heat to the cooler surrounding air), conduction (loss of heat to the colder contacted surfaces such as the OR table), convection (loss of heat due to circulating colder air), and evaporation (loss of heat due to evaporation for example from large open wounds). Answer B: Humidification devices attached to a patient's breathing circuit decrease heat lost through evaporation. However, as this is likely to be utilized during phase II of hypothermia, it is not the most effective way of preventing heat loss

Which of the following statements is MOST ACCURATe as it relates to the properties of N2O? A. In a full E cylinder at standard temperature, N2O exists in a liquid state as a result of being stored under pressure B. N2O containing E cylinders must be cooled to below 4 degrees celcius for storage C. N2O is naturally in a liquid form at standard temperature, and is aerosolized when being administered as part of an anesthetic D. The pressure gauge on a N2O containing E cylinder accurately estimates the amount of N2O remaining

A. In a full E cylinder at standard temperature, N2O exists in a liquid state as a result of being stored under pressure. Critical temperature is the temperature above which a gas can no longer be converted to a liquid form with increasing pressure alone. This property is inherent to a given gas. For N2O, this temperature is 36.5 degrees C. N2O exists in a gaseous state at standard room temperature and pressure. However, when placed under pressure, as in an E cylinder, it is converted into a liquid form provided the ambient temperature does not rise above 36.5 degrees C, which is typically the case in most ORs. In contrast, the critical temp of O2 is -119 degrees C, which is the reason why despite being stored under pressure in an E-cylinder in the OR, oxygen persists in a gaseous form. In order for oxygen to be liquified under pressure, it must be cooled to well below its critical temp, as would be the case in a liquid oxygen storage system which may be found in larger hospitals. *It is not necessary for N2O E cylinders to be cooled when used in an OR. At ambient temperature, N2O can be stored as a liquid when placed under pressure *N2O is a gas at standard temperature and pressure. When stored under pressure in an E cylinder in teh OR it exists as a liquid and a gas. N2O is removed from the E cylinder when used during an anesthetic; to replace the expended gas, liquid N2O must be continuously converted to a gaseous phase. As such the pressure within the E cylinder remains constant until the liquid volume is nearly exhausted

Which of the following is an appropriate INITIAL intervention for an incompetent respiratory valve? A. Increase FGF rate B. Increase minute ventilation C. Increase scavenging system suction D. Replace air and nitrous oxide with oxygen

A. Increase fresh gas flow rate Increasing fresh gas flow will help decrease the amount of exhaled gas that flows retrograde into the inspiratory system and thus will decrease the extent of rebreathing. Two critical components of a circle system that help prevent rebreathing of exhaled gases (namely CO2) are the inspiratory and expiratory unidirectional valves. When the inspiratory unidirectional valve is incompetent, it does not close fully during expiration. As a result, some of the patient's exhaled gas enters the inspiratory limb of the circuit. Then during the next inspiration, that gas will be rebreathed. The following findings on capnography are suggestive of (but not specific for) an incompetent inspiratory valve and should prompt the examination of the valve. 1. Elevated inspired carbon dioxide baseline 2. Prolonged expiratory platea, 3. Gradual (instead of sharp) inspiratory down stroke Additionally, spirometry can be used to diagnose an incompetent inspiratory valve. The measured exhaled tidal volume will be less than the expected value as the flow sensor is located within the expiratory limb of the circuit and will not detect the portion of exhaled gas that enters the inspiratory limb. Answer A: increasing fresh gas flow is the most important initial step in managing an incompetent inspiratory valve as it will limit or eliminate rebreathing. Increasing the fresh gas flow increases forward flow in the inspiratory limb, which makes it more difficult for exhaled gas to enter the inspiratory limb. Therefore, exhaled gas will preferentially flow into the expiratory limb of the circuit during exhalation.

Which of the following is MOST correct in regards to Doppler ultrasound? A. It can be used to determine both the direction and the speed of flow B. Misalignment of the ultrasound beam and blood flow will overestimate the blood velocity C. The view that provides the best two-dimensional image of a structure typically provides the best Doppler assessment of flow going through that structure D. When blood flows toward the ultrasound transducer, the reflected signal frequency is lower than that of the transmitted signal

A. It can be used to determine both the direction and the speed of flow The Doppler effect can be used in echocardiography to determine both the direction and the speed of blood flow. The Doppler effect is the shift in frequency of a reflected signal, caused by reflection on a moving particle. In the case of blood, the particles are the red blood cells. When the red blood cells move towards the transducer, the reflected signal will have higher frequency compared to the transmitted signal. By convention, blood moving away is represented in blue and blood moving towards the transducer is represented in red. The full equation is Delta f = v*cos(theta)*2f/c where f is the transmitted frequency, delta f is the shift between transmitted and received frequencies, v is blood velocity, c is the speed of sound in received frequencies, v is the blood velocity, c is the speed of sound in blood (1540 m/s), and theta is the angle of incidence between the ultrasound beam and blood flow. Since c is a constant, and assuming perfect alignment of the ultrasound beam to blood flow, then delta f represents blood velocity. As a corollary to that, the most important factor that is operator dependent and can negate the validity of Doppler measurements is beam alignment. With perfect alignment, the angel of incidence (theta) is zero, thus cos theta =1, but the more we deviate from perfect alignment (cos theta <1) the more we underestimate blood velocity. Note that because the theta to cos theta relation is not linear, the error does not equal the angle. Two dimensional images are optimal when the ultrasound beam is perpendicular to the structure of interest (for example aortic valve in short axis) because reflections on perpendicular structures produce strong, mirror-like reflections. However, it is parallel alignment that is optimal for flow through said structures (for example flow across the aortic valve in long axis). Answer B: with imperfect alignment of the beam, we will always underestimate (not overestimate) the velocity of flow. Answer C: the best view for two dimensional echo is perpendicular to the structure of interest, but the best orientation for Doppler flow determinations is parallel to the flow. Answer D: when blood flows toward the ultrasound transducer, the reflected signal frequency is higher (not lower) than that of the transmitted signal Bottom line: the doppler effect can be used to determine both the direction and speed of flow. Misalignment of the ultrasound beam will underestimate to blood velocity.

Which of the following is a requirement of pressure support ventilation? A. PSV can only be used in a spontaneously breathing patient B. PSV should not be combined with continuous positive airway pressure C. PSV should be used in respiratory distress because it increases the work of breathing D. PSV targets a specified volume regardless of lung compliance thus is useful in pulmonary edema

A. PSV can only be used in a spontaneously breathing patient. PSV is a ventilatory mode that is triggered by the patients' spontaneous effort and is assisted by a constant positive pressure. As such, PSV supports respiratory muscles and improves tidal volume for a given respiratory effort (the patient generates a greater volume than during spontaneous breathing). PSV can either be flow triggered or pressure triggered.

Which of the following measurements is useful to determine LV contractility by echocardiography? A. dP/dt B. E/A ratio C. LV mass D. Sphericity index

A. dP/dt There are many ways to assess cardiac function by echocardiography including EF, tissue doppler, systolic thickening of LV wall, and more modern methods such as 3D echo and speckle tracking dP/dt (rate of rise in ventricular pressure) is a good measure of cardiac contractility. The greater the contractile force, the faster the rise in LV pressure. First, there needs to be some degree of MR. The MR jet is interrogated with continuous wave doppler which will be displayed as MR jet velocity over time. Then using the simplified Bernoulli equation, velocity is converted to a pressure differential (equivalent to four times velocity squared). For example, if the MR jet takes 32 msec to increase from 1 m/s velocity (equivalent to 4 mm Hg) to 3 m/s (equivalent to 36 mm Hg) then it took 32 msec to increase by 32 mm Hg and the dP/dt value will be 1000 mm Hg/s Because measurements are taken during the isovolumic contraction phase (ie before the aortic valve opens), dP/dt is independent of afterload. E/A ratio is a diastolic measurement LV mass is useful to assess LVH rather than LV contractility. Interestingly, LVH is a stronger predictor for all causes of mortality than low EF. Sphericity index (long axis/short axis) is normally >1.5. It is reduced in dilated cardiomyopathy (the LV becomes more globular)

Pulse transit time

AKA photometric method, is a noninvasive modality that measures BP by measuring the time it takes for blood to travel between two transducers

A healthy 62 year old female is scheduled for a right total hip replacement due to severe osteoarthritis. The patient weighs 63 kg and has a starting Hgb of 14.5 g/dL. What is the allowable blood loss for this patient? Select one: a. 1884 mL b. 1966 mL c. 2240 mL d. 2498 mL e. 2604 mL

Acceptable blood loss is 1884 mL. For this, ABL is acceptable blood loss and EBV is estimated blood volume. Hgborig is original hemoglobin value and Hgballow is the allowable hemoglobin, that is the hemoglobin you wish to transfuse at or feel you should go no lower than to be safe. ABL = EBV x ((Hgborig-Hgballow)/(Hgborig)) EBV for an adult female = 60 mL/kg This patient weighs 63 kg EBV = 60 mL/kg x 63 kg = 3780 mL Hgborig= 14.5 Hgballow= 7 ABL = 3780 ((14.5-7)/(14.5))= 1965.6 = 1966 mL Since this patient is healthy and her only history is osteoarthritis we can use a transfusion trigger of 7 g/dL. Many geriatric patients that come in to the OR will have some type of underlying coronary artery disease. Most of the time patients will remain asyptomatic until there is an occlusion of > 70% of a coronary artery. So even though this patient is listed as healthy and the transfusion trigger has been decided to be 7 g/dL, you may need to transfuse earlier. The correct answer is: 1884 mL

Flow through ETCO2 analysis

Adapter placed in breathing circuit

What is the best muscle to monitor TOF after using non-depolarizing muscle relaxants?

Adductor pollicis is the best muscle to monitor when trying to determine whether a patient has sufficiently recovered airway reflexes and muscle tone

Administering 75% nitrous oxide to a patient with a 200 mL pneumothorax will expand the pneumothorax to what volume? Select one: a. 275 mL b. 350 mL c. 450 mL d. 675 mL e. 800 mL

Administering 75% nitrous oxide will expand closed air spaces to four times the original volume (in this instance to 800 mL). The amount of nitrous oxide that will diffuse into a closed air space will be that which results in an equal concentration of nitrous oxide to the inspired level. In this case, to get the concentration in the pneumothorax to be 75% nitrous oxide, the original air would only be 25% of the total air. Thus, 600 mL of nitrous oxide added to the 200 mL of air would result in the desired concentration. The total amount of gas in the pneumothorax would be 800 mL. The correct answer is: 800 mL

A 135 kg man is ventilated at a rate of 14 bpm with a TV of 600 mL and a PEEP of 5 cm H2O during a laparoscopic banding procedure. Peak airway pressure is 50 cm H2O and the patient is fully relaxed with NMBD. How can peak airway pressure be reduced without a loss of alveolar ventilation? Increase the inspiratory flow rate Take off PEEP Reduce the I:E ratio (e.g, change from 1:3 to 1:2) Decrease TV to 300 and increase rate to 28

After eliminating reversible causes of high peak airway pressures (occlusion of the ETT, mainstem intubation, or bronchospasm) adjusting the ventilator can reduce the peak airway pressure. Increasing inspiratory flow rate would cause the airway pressures to go up and would produce higher peak airway pressures. Removing PEEP would lower peak pressure at the expense of alveolar ventilation. Changing the I:E ratio from 1:3 to 1:2 will permit 8% (25% inspiratory time to 33% inspiratory time) more time for the TV to be administered and will result in lower airway pressures. Decreasing the VT to 300 and increasing the rate to 28 would give the same minute ventilation but not the same alveolar ventilation. Recall that alveolar ventilation equals (frequency) times (TV-deadspace) and because deadspace is about the same 2 ml/kg/min, alveolar ventilation would be reduced, in this case to a dangerously low level.

Potential hazards of vaporizers

Agent with higher VP in a vaporizer designed for agent with a lower VP = OVERDOSE Tipping of vaporizer: liquid agent enters bypass chamber--INC output = overdose At very low (not pushing agent) or high (not saturated) flows: output is less than dial setting Pumping effect: PPV or use of O2 flush valve--gas compressed by back pressure-- pressure released by bypass chamber--INC output

General vaporizer principles

Agent-specific with regard to VP, specific heat, & thermal conductivity VP is determined by temp and physical properties of liquid

Boiling point note (true learn)

All gases (ie all substances existing in gaseous phase at standard temperature and pressure) must, by definition, have a boiling point below room temperature. Although this must be true in order for N2O to exist as both liquid and gas in a medical gas cylinder, it does not best explain why nitrous oxide can exist in two phases while other gases do not. The boiling point of N2O is -88.5 C Bottom line: critical temperature is the temperature above which a gas cannot be liquified no matter the pressure applied. If the critical temperature of a medical gas is above room temperature (eg. N2O 36.4 C and CO2 31.1 C) the gas can potentially exist in both liquid and gas forms at room temperature when compressed in a medical gas cylinder. If the critical temperature is below room temperature (eg oxygen -119) the gas will never liquify at room temperature

The reason CO2 measured by capnometer is less than the arterial PaCO2 value measured simultaneously is

Alveolar dead space The capnometer measures the CO2 concentration of respiratory gases. Today this is most commonly performed by infrared absorption using a sidestream gas sample. The sampling tube should be connected as close as possible to the patient's airway. The difference between the ETCO2 and the arterial PaCO2 is typically 5-10 mm Hg and is due to alveolar dead space ventilation. Because nonperfused alveoli do not contribute to gas exchange, any condition that increases alveolar dead space ventilation (i.e. reduced in pulmonary blood flow, as by pulmonary embolism or cardiac arrest) will increase dead space ventilation and the ETCO2-PaCO2 difference. Conditions that increase pulmonary shunt result in minimal changes in the PaCO2-ETCO2 gradient CO2 rapidly diffuses across the capillary alveolar membrane

General anesthesia is administered to an otherwise healthy 38 year old patient undergoing repair of a right inguinal hernia. During mechanical ventilation, the anesthesiologist notices that the scavenging system reservoir bag is distended during inspiration. The most likely cause of this is

An incompetent pressure-relief valve in the mechanical ventilator In a closed scavenging system interface, the reservoir bag should expand during expiration and contract during inspiration. During the inspiratory phase of mechanical ventilation, the ventilator pressure-relief valve closes, thereby directing the gas inside the ventilator bellows into the patients breathing circuit. If the ventilator pressure relief valve is incompetent, there will be a direct communication between the patient's breathing circuit and the scavenging circuit, causing either the reservoir bag to inflate during the inspiratory phase of the ventilator cycle

Inaccurate/accurate and precise/imprecise monitors (true learn)

An innaccurate but precise monitor can be recalibrated to be accurate, but an imprecise monitor cannot be improved by recalibration. Bottom line: A monitor can be precise, accurate, both, or neither. Accuracy is how close a value is to the true value. Precision is how repeatable the measurements are. In other words, accuracy is defined by the mean of the measurement, while precision is defined by the standard error of the measurement. An imprecise monitor cannot be improved by recalibration.

What is an intraventricular conduction delay? When is it seen?

An intraventricular conduction delay is a wide QRS that arises from supraventricular conduction that is neither a typical RBBB nor a typical LBBB. It is often noted in patients with a cardiomyopathy

The correct location for placement of the V5 leads is

Anterior axillary line, fifth intercostal space

A patient on a ventilator with ascending bellows receives approximately how much PEEP due to the weight of the bellows? Select one: a. 1 cmH2O b. 3 cmH2O c. 5 cmH2O d. 7.5 cmH2O e. 10 cmH2O

Ascending bellows ventilators usually deliver 2 to 3 cmH20 PEEP due to their weight. The correct answer is: 3 cmH2O

Ascending bellows ventilators typically have how much PEEP?

Ascending bellows ventilators usually deliver 2-3 cm H2O due to their weight

Fresh gas flow on an anesthesia machine is set to 1 L/min with 100% oxygen. The dial on an isoflurane vaporizer is set to 1.2%. What is the gas flow through the vaporizing chamber? Select one: a. 12 mL/min b. 38 mL/min c. 54 mL/min d. 62 mL/min e. 100 mL/min

At 1 L/min total fresh gas flow, an isoflurane vaporizer set to 1.2% would allow 38 mL/min of gas flow through the vaporizing chamber. Variable bypass vaporizers are used to administer sevoflurane, isoflurane, halothane, and enflurane. Variable bypass means the fresh gas flow through the vaporizer is split into two streams: one that flows through the vaporizing chamber (picking up anesthetic gas) and one that flows through the bypass chamber. The two streams are reunited at the vaporizer outlet where the fresh gas flow (now carrying anesthetic gas) continues through the breathing circuit to the patient. The vaporizing chamber contains liquid volatile agent as well as agent vapor. The vapor is at a concentration determined by its saturated vapor pressure (which is the partial pressure of the vapor when it is at equilibrium between liquid and vapor states). Saturated vapor pressures for sevoflurane, isoflurane, halothane, and enflurane are 160, 240, 243, and 170 mm Hg, respectively. This means that a vaporizing chamber filled with sevoflurane will have a vapor pressure of 160 mm Hg or a concentration of 21% (concentration = saturated vapor pressure/atmospheric pressure X 100% = 160 mm Hg/760 mm Hg X 100% = 21%). That is much higher than the concentration needed for anesthesia (about 2%). No matter what flow of gas passes through the vaporizing chamber, the concentration of the gas leaving the vaporizing chamber will be 21% sevoflurane. This gas stream must be diluted to safe anesthetic levels by the fresh gas flow passing through the bypass chamber. The ratio of gas flow through the vaporizing chamber to the gas flow through the bypass chamber is referred to as a splitting ratio. The concentration dial adjusts the splitting ratio. For sevoflurane, in order to get a final concentration of say 2.1%, one-tenth (2.1%/21% = 1/10) of the total fresh gas flow must go through the vaporizing chamber. So if the total fresh gas flow is set to 1 L/min and the dial setting is at 2.1%, 100 mL/min of FGF will flow through the vaporizing chamber and the remaining 900 mL/min will flow through the bypass chamber. A useful equation for calculating splitting ratios:Flow through vaporizing chamber = Total FGF X [(Dial setting/100)/(Sat VP/Atm P)] For the scenario presented in this question:Flow through vaporizing chamber = 1 L/min X [(1.2/100)/(240 mm Hg/760 mm Hg)]Flow through vaporizing chamber = 1 L/min X 0.038 = 0.038 L/min = 38 mL/min The correct answer is: 38 mL/min

What dial setting on a desflurane vaporizer that has been calibrated at sea level will deliver 6% desflurane in Leadville, Colorado (elevation 10,000 ft with atmospheric pressure 69% of that at sea level)? Select one: a. 4.2% b. 5.6% c. 6.0% d. 7.8% e. 8.7%

At an altitude 10,000 feet above sea level, a desflurane vaporizer (calibrated at sea level) that is dialed to 8.7% will deliver an actual concentration of 6%. All variable bypass vaporizers, as used with sevoflurane, isoflurane, halothane, and enflurane, automatically compensate for altitude changes. However, the desflurane vaporizer, which is a dual-gas blender, does not automatically adjust for altitude changes. In order to calculate the required dial setting to deliver a certain concentration of desflurane, use the following equation: Required dial setting = Normal dial setting X (Calibration atmospheric pressure/Ambient pressure) Substituting the given information gives this: Required dial setting = 6% X (1 atm/0.69 atm) = 8.7% The correct answer is: 8.7%

When should central venous pressure be measured?

At the end of expiration

The use of hyperbaric therapy for treatment of patients with gas emboli is most associated with which of the following gas laws? A. Avogadro B. Boyle C. Charles D. Gay-Lussac

B. Boyle Boyle's law says that changes in gas volume is inversely related to the pressure on the gas. As pressure increases, the volume will decrease. If the pressure doubles, the volume will decrease by half. Hyperbaric therapy relies on increased environmental pressure to decrease the volume of gas emboli to reduce its effect on the body and speed up the recovery/healing process Gas emboli or pockets will increase or decrease in size depending on the pressure being exerted on them. In hyperbaric therapy, the increased environmental pressure on gas emboli results in a reduction in its volume to hasten resolution of symptoms. The Boyle law can also be appreciated with ETT cuff sizes and changes in altitudes. Increases in altitude from sea level will result in a decrease in the atmospheric pressure. Assuming all else is held constant, the volume within the cuff should increase as a result of the drop in pressure.

A 62 year old patient with chronic obstructive pulmonary disease (COPD) due to longstanding tobacco abuse presents in a COPD exacerbation. Noninvasive positive pressure ventilation is initiated and intitial blood gasses demonstrate a PaO2 ranging between 90-100 mmHg on room air while on 5 cm H2O expiratory positive airway pressure and 10 cm H2O inspiratory positive airway pressure. Which of the following errors in the handling of a subsequent arterial blood gas sample would be MOST likely to result in an artificially increased PaO2? A. Delaying sample analysis for 20 minutes B. Entraining an air bubble into the sample syringe C. Exposing the sample to fluorescent lighting D. Placing the sample in ice prior to analysis

B. Entraining an air bubble into the sample syringe The presence of an air bubble in the syringe that contains blood for an ABG will result in a change in the measured PaO2 towards the PO2 of the gas in the bubble, as well as a decline in the measured PaCO2. IN this case, where the measured PaO2 had been 90-100 mmHg, the entrainment of room air (PaO2 of about 159 mmHg) into the aliquot of sample blood will result in a falsely elevated PaO2 reading when analyzed by the blood gas analyzer. Bottom line: delays in analysis and exposure of a sample to room air are the two most common sources of error in blood gas analysis. A delay will result in decreased PaO2, pH, and base excess values and an increase in PaCO2. Entrainment of room air will tend to cause the PaO2 value of the sample to approach the PO2 of room air (159 mmHg at sea level) and result in a decreased measured PaCO2.

Anesthesia is induced and pt intubated without complication and patient is maintained on inhaled isoflurane. Following intubation, patient is placed on standard semi-closed anesthesia delivery system and provided PPV with 100% FiO2. FGF is decreased from 2.5 L/min to 0.25 L/min. Which of the following is most likely to occur with the change? A. Increased expired CO2 rebreathing B. Increased isoflurane rebreathing C. Increased ISO vaporizer output D. Increased waste scavenging

B. Increased isoflurane rebreathing A decrease in FGF rate to inject only the oxygen required to meet the metabolic demand of this adult patient effectively converts a semi-closed circle anesthesia circuit into a closed circuit. This results in almost complete expired gas rebreathing and negligible waste gas scavenging. The classic circle system incorporates multiple components that allow inspiratory and expiratory gasses to flow in a single direction around the anesthesia circuit. The essential components of a semi-closed circle system include a fresh gas inlet source, a unidirectional expiratory and inspiratory valves with tubing, a Y piece that connects this tubing to the pt, an overflow valve, a reservoir bag, and carbon dioxide absorbent. The extent of rebreathing of expired gases in this system is inversely related to FGF rate. AS more fresh gas is injected into the system, it effectively displaces more gas from the circuit, decreasing the amount of gas that is rebreathed. Thus, higher FGF rates result in greater waste gas scavenged by the scavenging system. It should be noted that CO2 absorbent selectively removes CO2 from the expired gas so regardless of the FGF, no CO2 is ideally entering the inspiratory limb of the system. Benefits of high FGF in a semi-closed system include less accumulation of potentially toxic endogenous gases including carbon monoxide, acetone, and methane, as well as less potential accumulation of toxic absorbent degradation products like compound A or carbon monoxide. High FGF rates come at the cost of decreasing the amount of anesthetic gas returning to the inspiratory limb of the circuit and therefore utilize more inhaled agent than lower rates. Heat and moisture are also displaced in a high FGF rate scenario and are lost to the scavenger. As flow rates decrease, the opposite effects also occur. Heat and moisture are conserved in the circuit and less anesthetic gas is output from the vaporizer, but more potentially toxic substances accumulate in the circuit. The minimum possible FGF rate that is compatible with a normoxic inhaled gas mixutre is the pts basal metabolic rate of O2 consumption. This value is typically between 3-4 ml/kg/min in an adult but can be as high as 8-10 ml/kg/min in a premature infant or neonate. Injection of 100% O2 at this rate into a semi-closed circle anesthesia delivery system converts the system into a closed circuit. No gas is wasted or scavenged in this scenario as all fresh gas input (O2) is consumed by the patient and converted to exhaled CO2 that is absorbed by the CO2 absorbent. No more inhaled anesthetic agent is added into the system as the amount that is in the system is constantly rebreathed. The closed system achieves max advantage of Low FGF anesthesia, however, it is very difficult to achieve in practice. The risk of delivering a hypoxic inhaled gas mixture is significant, and the risk of accumulating toxic metabolites and endogenous gases is also present. That said, this situation represents the maximal retention of heat and moisture in the breathing circuit and utilizes the minimum amount of anesthetic gases of any anesthetic technique. *A functioning CO2 absorbent prevents rebreathing of CO2 in the inspiratory lim of the circle system regardless of FGF

Which of the following BEST describes the risk of utilizing airway pressure release ventilation (APRV) in a patient without spontaneous respiratory drive? A. Increased risk of atelectotrauma B. Increased risk of hypercarbia C. Increase risk of pulmonary edema D. Increased risk of volutrauma

B. Increased risk of hypercarbia Airway pressure release ventilation (APRV) is an advanced ventilator mode that is characterized as an inverse ratio mode that is pressure controlled with intermittent mandatory ventilation and unrestricted spontaneous breathing. While the mode can be utilized in a deeply sedated or paralyzed patient without a spontaneous respiratory drive, the main purpose of this mode is to allow for an "open lung approach" to spontaneous ventilation in order to optimize V/Q matching and improve oxygenation. Due to the characteristic extreme inverse I:E ratio utilized in this mode (>2:1), in patients who are unable to supplement intermittent mandatory breaths with their own spontaneous effort, hypoventilation, and therefore hypercarbia is common. APRV can be thought of as dynamic continuous positive airway pressure (CPAP) and shares much in common with biphasic positive airway pressure ventilation (BPAP) ventilation. Similar to BPAP parameter that are set in this mode include P-high, P-low, T-high, T-low, and FiO2. With respect to these setting, the "P" values represent airway pressures, and the "T" values represent the time that the patient spends at that pressure. In APRV, the goal is to maintain a patient within the steep portion of the pressure-volume curve. During positive pressure inspiration, there exists an initial period of recruitment where increases in pressure produce little change in volume. Following lung recruitment, volume increases steeply for small changes in pressure. The point at which this initially occurs is called the lower inflection point. As lung volume increases with increasing pressure, eventually it will reach a state of over distention, and further increases in pressure will not result in significant increases in lung volumes. The point at which this occurs is called the upper inflection point. Repeated administration of airway pressures below the lower inflection point can result in atelectotrauma, and repeated airway pressures above the upper inflection point place the patient at risk for volutrauma. In general, the modern practice of mechanical ventilation aims to maintain airway pressures between these two points.

You are asked to lead a Root Cause Analysis into a recent incident at your hospital where a patient narrowly avoided severe injury from an OR fire. After an initial round of fact-finding, you conclude that the most likely ignition of the fire was due to static electricity discharge. As you continue with your analysis, you consider modifiable operating room factors that could have an effect on the risk of static discharge. Which of the following factors would MOST LIKELY REDUCE the risk of a static discharge occurring in the OR? A. Maintaining an OR temperature no more than 70 degrees fahrenheit B. Maintaining OR relative humidity between 50-55% C. Reminding staff to discharge any built up static charge prior to touching the patient D. Requiring all OR staff to stop wearing conductive shoes to work

B. Maintaining OR relative humidity between 50-55% Maintaining an ideal relative humidity level in the OR of 50-55% can help significantly mitigate conditions that may lead to an increased risk of static discharge.

Which of the following ETT materials is most vulnerable to ignition when exposed to a CO2 laser? A. Nylon B. Polyvinyl chloride C. Red rubber D. Silicone

B. Polyvinyl chloride Nylon and red rubber are less combustive than PVC Silicone was the most combustion-resistant of materials examined

Which of the following is MOST likely to lead to an overdose of volatile anesthetic? A. Loose filler cap on the vaporizer B. Pouring isoflurane into the sevoflurane vaporizer C. Using the vaporizer interlock system D. Vapor leak into fresh gas flow line

B. Pouring isoflurane into the sevoflurane vaporizer Pouring isoflurane into a sevoflurane vaporizer is most likely to lead to an overdose of volatile anesthetic. This is due to 1. The larger vapor pressure of isoflurane 2. The increased potency of isoflurane compared to sevoflurane. Sevoflurane has a relatively low vapor pressure of 160 mm Hg at 20 C compared to 240 mm Hg for isoflurane. Therefore, there will be proportionally more molecules of isoflurane in the vapor phase and the output concentration of isoflurane will be greater than what is set on the "sevoflurane" vaporizer concentration dial. The use of an anesthetic agent analyzer (eg infrared absorption spectrophotometry) would alert the provider to such an error. Modern vaporizers have a variety of safety features that have minimized or eliminated many of the hazards once associated with variable bypass vaporizers. The safety features include: 1. Push/release button that must be activated before vaporizer can be turned on which prevents accidental delivery of an agent 2. Interlock system that prevents more than one vaporizer being on at the same time 3. Keyed fillers with unique sizing which prevent filling with the wrong agent 4. Color coding of agents (iso-purple, sevo-yellow, des-blue, halothane-red, enflurane-orange) 5. Low filling points to prevent overfill 6. Secured vaporizers to manifold to prevent tipping 7. Universal direction of activating vaporizers in a counter-clockwise direction (right tighty, lefty loosey) Despite all the safety features, some vaporizers leak gas into the outflow channel even when turned off. These small amounts to not produce any appreciable clinical effect, but have potential to trigger MH. Therefore, the vaporizers should be removed from the machine entirely in cases with susceptible individuals. Answer A: A loose filler cap is the most common source of a vaporizer leak. Rather than leading to overdose, leaks in the vaporizers can result in underdose and patient awareness in anesthesia, along with provider exposure to the agent. The negative pressure leak test is a part of the daily machine check and is designed to determine sumch leaks, especially in the GE-Datex-Ohmeda machine due to the presence of check valve just upstream to the common gas outlet. This prevents the low-pressure system in the anesthesia machine from being tested with the positive pressure leak test. Answer C: the interlock system actually reduces the risk of overdose by preventing simultaneous administration of more than one inhaled anesthetic. When the control dial is turned on, a rod on both sides of the vaporizer is released which immobilizes the dials of adjacent vaporizers. Answer D: Vapor leak into the outflow channel line may occur even if the vaporizer is off and would theoretically increase the amount of volatile agent delivered. However, these small amounts do not produce any appreciable clinical effect. The exception is in patient's susceptible to MH, which is why removal of the vaporizers is recommended or using a machine that has not had vaporizers connected previously. TrueLearn Insight: If a vaporizer has been tipped, it should not be used clinically until it has been purged for 20-30 minutes using a high fresh gas flow with the vaporizer concentration dial set at a high concentration.

How wide/long should the BP cuff be?

BP cuff diameter should be 40% of arm circumference Length ~80%

What are some complications of PA catheters?

Bacteremia, endocarditis, thrombogenesis, pulmonary infarction, pulmonary artery rupture, hemorrhage, dysrhythmias, conduction abnormalities, valvular damage

A ventilator pressure-relief valve stuck in the closed position can result in

Barotrauma The ventilator pressure-relief (spill) valve is pressure controlled via pilot tubing that communicates with the ventilator bellows chamber. As pressure within the bellows chamber increases during the inspiratory phase of the ventilator cycle, the pressure is transmitted via the pilot tubing to close the pressure relief valve, thus making the patient's breathing circuit "gas tight". This valve should be open during the expiratory phase of the ventilator cycle to allow the release of excess gas from the patients breathing circuit into the waste-gas scavenging circuit after the bellows has fully expanded. If the ventilator pressure-relief valve were to stick in the closed position, there would be a rapid buildup of pressure within the circle system that would be readily transmitted to the patient.

Kinking or occlusion of the transfer tubing rom the patient's breathing circuit to the closed scavenging system interface can result in

Barotrauma A scavenging system with a closed interface is one in which there is communication with the atmosphere through positive-pressure and negative-pressure relief valves. The positive-pressure relief valve will prevent transmission of excessive pressure buildup to the patient's breathing circuit, even if there is an obstruction distal to the interface or if the system is not connected to wall suction. However, obstruction of the transfer tubing from the patient's breathing circuit to the scavenging circuit is proximal to the interface. This will isolate the patient's breathing circuit from the positive pressure relief valve of the scavenging system interface.

Insufflation

Blowing of anesthetic across pts face

Gas inlets and pressure regulators

Bourdon pressure gauge for cylinders Pressure regulators 1. 1st stage limit pipeline (50 psi) and cylinder (45 psi) pressures. Pressure gradient allows use of pipeline O2 preferentially over cylinder when both are open 2. 2nd stage maintains gas flow at a constant pressure to flow meters (~14 psi)

What color is a helium tank?

Brown

Which of the following design features is most likely to be found in modern ETTs? A. low volume, high pressure cuff B. Silicone construction C. Ultra-thin polyurethane cuff D. Universal 20 mm external diameter ventilating circuit

C. Ultra-thin polyurethane cuff ETT cuffs made from ultra-thin polyurethane have been shown to prevent liquid flow around an ETT cuff while only inflated to 15 cm H2O. Standard ETTs are disposable, single use, cuffed, clear polyvinyl chloride (PVC) plastic tubes that are designed to be inserted via either the oral or nasal route. All tubes include a universal 15 mm external diameter ventilating circuit adapter that allows the tube to be connected to standard ventilating circuits and devices. Ultra-thin polyurethane (10 microns) has been shown to prevent passage of fluid past the cuff at 15 cm H2O, compared to the traditional 30 cm H2O seen in standard thickness PVC cuffs (50-80 microns) PVC has largely replaced silicon in the construction of modern ETTs. Benefits= low cost, transparency, and conformation to the pts anatomy when warmed in the oropharynx

Which of the following BEST describes an open waste scavenging interface system? A. Positive pressure from the gases leaving teh gas collecting assembly provides waste gas flow through the interface B. Negative pressure relief valves are required for safe operation C. Vacuum rate must exceed the rate of waste gas flow into the reservoir chamber D. Waste gas is passively vented through a hose to the outside of the building

C. Vacuum rate must exceed the rate of waste gas flow into the reservoir chamber An open waste gas scavenging interface does not utilize positive pressure or negative-pressure relief valves but is instead open to the atmosphere. Because of this, the vacuum rate within the canister must exceed the rate of waste gas flow into the reservoir chamber. Inadequate vacuum flow will result in waste gas spilling into the procedural environment through the atmospheric ports. Waste gas scavenging systems are a critical part of an anesthesia machine, but their importance may often be overlooked. Because the fresh gas flow rates of modern semi-closed open anesthesia circuits, more volatile agent is collected from the vaporizer than is necessary and more oxygen tends to be administered to the patient than can be consumed. Without a scavenging system, these gasses would be vented into the procedural area at levels that exceed published occupational safety standards. Even with a scavenging system in place, leaks in the anesthesia circuit or a poor mask seal may result in contamination of the operating environment with halogenated agents. Waste gas scavenging systems normally comprise 5 components. These are the gas collection assembly, the transfer tubing, the scavenging interface, disposal tubing, and the disposal assembly. Of these the most crucial to the effective and safe functioning of a waste gas scavenging system is the scavenging interface itself. This is because the scavenging interface acts as a relief valve for the entire respiratory circuit by protecting the circuit from positive or negative pressure. Scavenging interfaces tend to be broken down based on two main classifications. These are active or passive systems, or open or closed interfaces. All scavenging interfaces must incorporate positive pressure relief in order to protect the breathing circuit and the patient from excessive positive pressures. These allow the system to vent in the case of scavenging system occlusion or inadequate suction if an active system is being utilized. In the event of a scavenging system occlusion, the fresh gas flows from the anesthesia machine will continue to entrain air into the breathing circuit eventually building up potentially dangerous levels of pressure in teh absence of the usual relief provided by the scavenging system. Negative pressure relief valves are required in all active closed scavenging interfaces, as wall suction could induce subatmospheric pressures into the breathing circuit resulting in patient injury. Active scavenging systems incorporate a central wall suction system to remove gases from the anesthesia circuit. Passive systems simply utilize the slight positive pressure gradient generated during exhalation of gases to vent the waste gas out of the OR, either through a wall or into a return duct for a nonrecirculating hospital ventilation system. Open interfaces utilize an open canister. Waste gases are piped into the bottom of the canister next to the intake for the central suction system The vacuum flow outflow should exceed the flow of the waste gas inflow and some room air should be entrained into the system during normal operation. Because these systems are open to the environment, they do not require positive or negative pressure relief valves, but instead simply vent any excessive positive pressure back into the procedural area if wall suction fails. Closed interfaces are similar but may require positive and negative pressure relief valves both for isolation from the environment and pressure relief in the event of system malfunction. In passive closed systems, only a positive pressure relief valve is required as no suction is applied to they system. In active closed systems, the addition of a negative pressure relief valve is required for safety.

What is the Fick principle equation?

CO = VO2/(CaO2-CaVo2) Or CO= oxygen consumption/a-vo2 oxygen content difference Cardiac output equals oxygen consumption divided by difference in oxygen content

Eye protection for OR staff is needed when laser surgery is performed. Clear wraparound goggles or glasses are adequate with which kind of laser?

CO2 laser CO2 lasers can cause serious corneal injury, whereas argon, Nd:YAG, ruby or potassium titanyl phosphate lasers can burn the retina. Use of the incorrect filter provides NO protection. For argon or krypton laser light-amber-orange filters are used Nd:YAG laser light-special green tinted filters are used Potassium titanyl phosphate:Nd:YAG laser light-red filters

Transcutaneous oxygen and CO2 monitors

CO2 or clark electrode on skin directly measures gas diffusion out of skin which is correlated to arterial content heating element can cause burns if low perfusion or left in place to long

What is the differential diagnosis of low voltage on EKG?

COPD, hypothyroidism, pericardial effusion, anasarca, amyloidosis, ischemic cardiomyopathy, and obesity

A-fib CVP tracing (true learn)

CVP tracing contains 3 systolic components (c wave, v wave, x descent) and two diastolic components (a wave, y descent). In atrial fibrillation characteristic CVP = loss of a wave a prominent c wave

What will have the greatest effect on increasing oxygen content in the blood?

CaO2 = (PaO2 x 0.0031) + ([Hb] x SaO2 x 1.39) Increasing hemoglobin will by far have the highest effect on oxygen content in the blood The first part of the equation, regarding dissolved oxygen follows Henry's Law. Henrys law states that the concentration of gas in solution is directly proportional to the partial pressure of gas. The solubility coefficient determines how much of the gas is dissolved in solution --> for oxygen in blood the solubility coefficient is 0.003 mL/dl/mm Hg To find the amount of oxygen bound to hemoglobin, multiply the concentration of hemoglobin by the oxygen saturation and multiply the oxygen carrying capacity of hemoglobin Looking @ the equation it is clear that increasing the partial pressure of oxygen will not change oxygen carrying capacity greatly FiO2 increases will cause increases in PaO2 which again does not greatly increase oxygen content Increasing iron content could theoretically increase hemoglobin especially in iron-deficient anemic patient but it would not have the same quick impact as giving PRBCs

A TOF resulting in 4 out of 4 with no fade can still mean a neuromuscular blockade has what percent of receptors blocked?

Can still have 70% of receptors blocked

Why does carboxyhemoglobin not impact pulse oximetry readings?

Carboxyhemoglobin absorbs light @ the same wavelength as oxyhemoglobin which will lead to falsely reassuring SaO2 value

Effects of hypothermia

Cardiac dysrhythmias Left shift of oxyhemoglobin curve Reversible coagulopathy Stress response Altered mental status Impaired renal function DEC drug metabolism Poor wound healing

Copper Kettle Vaporizer

Carrier gas bubbled through Anesthetic copper is used to maintain a constant temp 1 ml of liquid produces ~200 mL vapor Measured flow vaporized (or flow-controlled vaporizer) Final concentration depends on total gas flow and flow through vaporizer

Which of the following would result in lower vaporizer output than dial setting? Select one: a. Changing fresh gas flow from 100% oxygen to 70% nitrous oxide/30% oxygen b. Low fresh gas flow c. Tipping the vaporizer during transport d. Overfilling the vaporizer e. Regularly calibrating the vaporizer

Changing fresh gas flow from 100% oxygen to 70% nitrous oxide/30% oxygen causes a transient decrease in vaporizer output. This transient decrease is due to the greater solubility of nitrous oxide in volatile anesthetic which reduces agent concentration by up to 20%. The concentration of output slowly increases and will actually result in slightly higher output over time. Low fresh gas flow less than 250 mL/min results in higher vaporizer output. Tipping and overfilling actually cause the bypass chamber to be contaminated with agent and thus increase vaporizer output. If this occurs, the vaporizer must be purged with high fresh gas flows for 20 to 30 minutes before use. Regularly calibrating the vaporizer will result in more accurate vaporizer output. The correct answer is: Changing fresh gas flow from 100% oxygen to 70% nitrous oxide/30% oxygen

Charles law

Charles law explains the relationship between volume and temperature where V1/T1 = V2/T2

What is the purpose of a check valve on the anesthesia machine?

Check valves permit only unidirectional flow of gases. These valves prevent retrograde flow of gases from the anesthesia machine or the transfer of gas from a compressed-gas cylinder at high pressure into a container at a lower pressure. Thus these unidirectional valves will allow an empty compressed-gas cylinder to be exchanged for a full one during operation of the anesthesia machine with minimal loss of gas.

Compare Open to room vs Closed to room waste gas scavenging system

Closed requires pressure-relief valve open does not

Closure of the inspiratory valve during exhalation is critical as it: Select one: a. Prevents venting of anesthetic gases into the operating room b. Prevents expiratory gas from contaminating fresh inspiratory gas c. Ensures expiratory gas is vented through the APL d. Prevents barotrauma due to an occluded scavenging hose e. Causes fresh gas flows to be sent through CO2 absorber

Closure of the inspiratory valve during exhalation prevents expiratory gas from contaminating fresh inspiratory gas. The inspiratory and expiratory valves work in concert to ensure flows travel correctly in the circle system. The inspiratory valve closes during expiration so that expired gases are sent to the carbon dioxide absorber or to the scavenging system in order to avoid mixing with and contamination of fresh inspired and CO2 scrubbed gases. The inspiratory valve is opened by inhalation, which closes the exhalation valve. When exhalation occurs, the inspiratory valve is closed. The correct answer is: Prevents expiratory gas from contaminating fresh inspiratory gas

What are some contraindications to pulmonary artery catheterization?

Complete LBBB WPW syndrome Ebsteins malformation (can cause tachy-arrythmias)--Ebsteins malformation is a rare heart defect in which the tricuspid valve doesn't work properly

What is compliance? How is it determined?

Compliance is a measure of distensibility and is expressed as the change in volume for a given change in pressure. Determination of compliance involves the interrelationship among pressure, volume, and resistance to airflow. Two relevant pressures that must be monitored during MV are peak and static resistance

Compliance (true learn)

Compliance, expressed as a change in lung volume divided by the change in pressure required to achieve said change in volume, can also be thought of as the inverse of elastance. Thus, a highly elastic lung is one that has low compliance, as is the case with fibrosis. Conversely, loss of elastic lung tissue results in increased compliance, as observed in emphysema Static compliance- refers to the compliance of lung tissue during periods without gas flow (for example, during an inspiratory hold on a mechanically ventilated patient) Cstat = VT/(Pplat - PEEP) Dynamic compliance- refers to compliance of lung tissue during gas flow. Cdyn = VT/(PIP - PEEP) --Decreases in dynamic compliance are observed in a variety of obstructions, such as obstruction of ETT, mucus plugging, or airway narrowing *Keep in mind: Because PIP is always higher than Pplat, the Cdyn for any given lung tissue is always lower than Cstat

Humidifiers & Neblizers

Conserve heat and water Condenser humidifier traps exhaled moisture which is released during inspiration (simple design) Bubble through humidifiers air exposed to warm water; risk of thermal injury Nebulizers- aerolize water particles -High pressure jet nebulizers produce produce droplets 5-30 microM - ultrasonic nebulizers produce droplets 1-10 microM

Flow control valves, flowmeters and electronic flow

Constant-pressure variable orifice flow meters- Thorpe tube Fixed orifice flow meters- commonly used for cylinders Hollow glass tubes with gradually INC inner diameter containing "float" Agent-specific per gas viscosity and density; calibrated individually to control flow rate Individual gas flows combine downstream from the flowmeters O2 flowmeters should be situated downstream from other gases (closest to the pt) to minimize the risk of hypoxic delivery in case of an upstream flow meter leak AT LOW FLOW RATES LAMINAR gas flow (viscosity) AT HIGH FLOW RATES TURBULENT gas flow (density)

Risk of electrocution

Contact with two conductive materials at different voltage potentials may complete circuit and result in electric shock

Continuous wave doppler

Continuous wave doppler used two dedicated ultrasound crystals, one for continuous transmission and second for continuous reception of ultrasound signals. This permits measurement of very high frequency doppler shifts or velocities. The COST is range ambiguity. In other words the precise location of peak velocity along the length of the doppler cursor is not definitely known. Instead, the clinician must infer the location of the highest velocity, such as a stenotic aortic valve. Continuous wave doppler is used for measuring high velocities. (stenotic valve or prosthesis)

Precordial and esophageal monitors

Contraindicated in pts with esophageal varicies or strictures Good for monitoring heart and breath sounds

List the uses of O2 in an anesthesia machine

Contributes to FGF Provides gas for the O2 flush Powers the low O2 alarm Controls the flow of nitrous oxide Powers the fail-safe valves Is the driving gas for the ventilator

The TRUE statement regarding ECG lead placement is: lead I displays the ECG signal recorded from the lift arm and right arm lead II displays the eCG signal recorded from the left arm and right leg lead III displays the ECG signal recorded from the left leg and right leg lead V1 displays the ECG signal recorded from a unipolar electrode placed in the 2nd intercostal space at the right midaxillary line lead V6 displays the ECG signal recorded from a unipolar electrode placed in the 4th intercostal space at the anterior axillary line

Correct: lead I displays the ECG signal recorded from the left arm and right arm Lead II is left arm and left leg lead III is right arm and left leg V1 is placed in the 4th intercostal space to the right of the sternum V6 is placed in the 5th intercostal space at the mid-axillary line

Macroshock

Current applied at skin 100 mA = cause V fib 10 mA = painful, aversive stimulus 1 mA = perception of shock

Microshock

Current applied inside the body 100 mA = cause V fib 10 mA = max leakage current

Bain system is a modification of which Mapelson circuit?

D

Which of the following IV dyes is least likely to cause falsely low pulse oximetry readings? A. methylene blue B. indocyanine green C. Indigo carmine D. Fluorescein

D. Fluorescein Fluorescein is a yellow-orange dye that minimally absorbs light at 660-940 nm. Certain dyes such as methylene blue, indocyanine green, indigo carmine, nitrobenzene, and lymphazurin/isosulfan blue are blue or blue-green dyes that absorb light significantly more at 660 nm than at 940 nm. the pulse oximetry interprets this as a greater concentration of deoxyhemoglobin (relative to oxyhemoglobin) and displays a falsely low oxygen saturation. Usually lasts ~30 minutes and is dependent on the rate of dye clearance

When blood flows through a non-atherosclerotic section of artery, which of the following changes would lead to the greatest reduction in flow? A. Double the blood viscosity B. Double the radius of the artery C. Halve the blood viscosity D. Halve the radius of the artery

D. Halve the radius of the artery Poiseuille Law states that: Q = P(pi x radius^4)/(8 x viscosity x length) Equivalent changes in the radius as compared to other parameters, will make the most impact on overall flow through the vessel. The radius of the vessel is directly proportional to flow and inversely proportional to resistance. This relationship is only truly valid in the setting of laminar, non-turbulent flow through a constant tubular cross section, but can be used to make multiple assumptions in human circulation and respiratory gas flow. Laminar flow occurs when fluid flows through a tube in parallel layers that do not intersect. Intersection of these layers of flow would indicate turbulence. Doubling blood viscosity or length of the artery would only halve the flow. Decreasing the blood viscosity or increasing the radius of the artery would each increase the flow. Answer B: this would exponentially increase the blood flow. Flow and radius and directly proportional

Which of the following non-invasive monitoring modalities MOST enables providers to continuously monitor for both cerebral hyperperfusion and atherosclerotic plaque emboli burden in a patient undergoing carotid endartectomy? A. Cerebral oximetry B. Four channel electroencephalogram (EEG) C. Somato-sensosry evoked potentials D. Transcranial Doppler Ultrasound

D. Transcranial Doppler ultrasound Transcranial Doppler (TCD) ultrasound monitoring measures two parameters during carotid vascular surgical procedures: blood flow velocity in major arteries (normally the middle cerebral artery [MCA]) that lead to the cerebral cortex, as well as the number of atherosclerotic emboli detected in the same vessel. Other noninvasive global cerebral blood flow techniques are unable to perform both of these measurements. Neurologic monitoring in a patient undergoing carotid endarterectomy is primarily utilized to promptly identify changes in cerebral blood flow (CBF) to prevent brain hypoperfusion while a carotid artery is clamped. This monitoring is utilized to guid both surgical interventions (eg carotid shunt placement) and the maintenance of anesthesia (eg. increasing cerebral perfusion pressure). Survival of brain cells is not compromised until CBF decreases to about 12 mL/100 g/minute in the awake patient, while various anesthetic agents may have a protective role in preventing neuronal injury and may allow this number to drop even lower. EEG is often though of as the "Gold Standard" for detection of electricla brain activity perturbations attributed to decreases in CBF during CEA. This arises from studies in the 1970s that validated EEG against the true gold standard of CBF measurement, Xe radiotracer washout method. While these studies demonstrated that EEG was adequate to detect regional changes in CBF, because of the extremely low incidence of intraoperative stroke, no prospective study has validated EEG to reduce the incidence of stroke during CEA. SSEPs generally remain intact until CBF decreases to under 15 mL/100g/minute. This is an additional monitor that has been shown to have a similar clinical efficacy to EEG when selective shunting (shunting patients undergoing CEA when intraoperative evidence of cerebral hypoperfusion arises) is utilized. Also, as the SSEP signal if averaged over minutes instead of instantaneously as in EEG, SSEPs may have a lower failure rate than eEG, but clinically these two monitoring modalities are very similar. TCD monitoring utilized ultrasonography to most often image the MCA by obtaining a view window through the temporal bone. Utilizing the Doppler effect, the flow velocity of red blood cells in the MCA can be approximated. Because this is an ultrasound monitor, atherosclerotic emboli burden can be quantified by counting the number of high-intensity transient signals (HITSs) that the highly echogenic emboli generate as they pass through the plane of the ultrasound doppler. The use of this monitoring modality makes two major assumptions regarding CBF. First is that velocity of blood flow correlates with CBF, and the second is that increasing embolic burden increases the likelihood of cerebral injury. The first assumption is controversial, but the second has been borne out in multiple studies. Cerebral oximetry, or near-infrared spectroscopy (NIRS), is a monitor that is simple to both apply and interpret. It operates under the principle that as less oxygen is delivered to the brain due to decreased CBF, more oxygen is proportionally extracted from cerebral arterial blood, and therefore oxygen saturation in cerebral venous blood will decrease. Practically, this monitor is applied as a pad across the forehead and detects oxygen saturaiton in cerebral venous blood across the prefrontal cortex. While in theory this monitor seems useful in detecting decreased oxygen delivery to the brain and may prevent intraoperative cerebral injury, the data regarding its use in this capacity is mixed.

Which of the following is MOST likely to adversely affect the accuracy of cardiac output monitoring by thermodilution? A. High CO state B. High injectate volume C. Low injectate temperature D. Tricuspid regurgitation

D. Tricuspid regurgitation Tricuspid regurgitation will tend to reflux the cold injectate within the right side of the heart during thermodilution monitoring, and thus will tend to under-estimate the cardiac output. The invasive determination of CO by thermodilution is considered on of the gold standards for the measurement of this physiologic parameter. This technique utilizes the rapid injection of an aliquot of fluid of a known temperature into the right side of the heart to estimate the volume of a fluid moving through the pulmonary artery over time. Typically, this consists of 10 mL of room temperature crystalloid injected into the right side of the heart. Changes in PA temperature are detected by a thermistor probe embedded at the tip of the PA catheter, and with this temperature information, the volume of blood passing through the PA over time can be determined. Because the full cardiac output passes through the PA during each cardiac cycle, this measurement estimates the cardiac output. This measurement is intrinsically prone to error, and it is standard practice to perform multiple thermodilutions in series to generate an average. It is generally accepted that differences of less than 10% from measurement to measurement are not considered to be clinically significant. Due to this intrinsic variability, it is essential that those performing this analysis understand the means by which the signal-to-noise (S/N) ratio can be maximized when performing this study. High cardiac output states allow for movement of the cold aliquot of fluid to be carried through the RV in a rapid and predictable fashion. Lower cardiac output states (CI of less than 2.5 L/min/m2) introduce more time for cold absorption by tissues other than blood. In addition to low cardiac output states, examples of intra-cardiac pathologies that adversely effect the S/N ratio of thermodilution include tricuspid regurgitation and intra-cardiac shunts. Tricuspid regurgitation will tend to underestimate the cardiac output by prolonging the time that the injected thermal signal is detected by the PA thermistor probe due to reflux of the thermal signal from the right ventricle. Both left-to-right and right-to-left shunts will tend to overestimate CO by either rapidly diluting the thermal signal or by shunting the signal away from the thermistor respectively.

Which of the following is a true statement regarding the line isolation monitor? A. It monitors the integrity of the grounded power source in the OR B. The line isolation monitor alarms when the leakage is less than 2 milliamps C. The secondary circuit is grounded, while the primary circuit remains ungrounded D. When a second fault occurs, a shock is present

D. When a second fault occurs, a shock is present The following are characteristics of line isolation monitors (LIM) 1. Monitors the integrity of the ungrounded power source in the OR 2. The primary circuit is attached to the ground, but the secondary circuit is not 3. The LIM alarms when the leakage current is greater than 5 milliamps 4. A first fault is not a shock hazard, but a second fault is a hazard to OR personnel. If there is an alarm after the procedure has begun, the most appropriate next step is to unplug the electrical device which was most recently plugged in

Double burst stimulation with peripheral nerve stimulator

DBS 3,3: 3 short 200 msec bursts @ 50 Hz followed by 750 msec later by another 3 bursts DBS3,2: 3 short 200 msec bursts @ 50 Hz followed 750 msec later by another by another 2 bursts DBS is more sensitive than TOF

What are some causes for PAOP to be less than LVEDP?

DEC LV compliance Aortic insufficiency

Underdampened Waveform

DF <0.7 Ringing waveform results Systolic OVERestimated

What percent desflurane is present in the vaporizing chamber of a desflurane vaporizer (pressurized to 1500 mm Hg and heated to 23 C)?

Desflurane is unique among the current commonly used volatile anesthetics because of its high vapor pressure of 664 mm Hg. Because of this high vapor pressure, the vaporizer is pressurized to 1500 mm Hg and electrically heated to 23C to give more predictable concentrations: 664/1500 = 44% If desflurane were used at 1 atm, the concentration would be about 88% 664/760=88%

DISS

Diameter index safety system--connection from pipeline to machine

Muscle recovery from NMB

Diaphragm, rectus abdominis, laryngeal adductors and orbicularis oculi recover before adductor pollicis

General description of mapelson circuits

Differ in fresh gas tubing, mask, reservoir bag, tubing, and expiratory valve locations Characterized by: 1. No valves directing gases to and from pt 2. No CO2 neutralization

Diffusion of a gas is inversely proportional to the: Select one: a. Temperature b. Membrane surface area c. Existing partial pressure gradient d. Membrane thickness e. Gas solubility

Diffusion of a gas is inversely proportional to the membrane thickness. All of the other choices are factors that are directly proportional to the rate of gas diffusion. Ficks Law of Diffusion simply states that the rate of diffusion of a gas is directly proportional to the concentration gradient (or the difference in partial pressures of the gas) across the tissue membrane. In other words, the greater the difference in concentration, the faster the gas diffuses. However, other factors do affect gas diffusion and are often included in the definition of Ficks Law of Diffusion. Diffusion is also directly proportional to membrane area and the gass diffusion constant (which includes gas solubility and temperature). As these factors increase, diffusion also increases. Diffusion is inversely proportional to membrane thickness and the square root of the gass molecular weight (which is known as Grahams Law). As these factors increase, diffusion decreases.Thus, the ideal membrane for diffusion is thin but has a very large surface area. The alveoli of the lungs have a substantial total surface area of 50-100 square meters and a very small thickness of only 0.3 micrometers making it the ideal organ for diffusion. The correct answer is: Membrane thickness

A 45 year old patient recovering in the ICU after a MVA is continuously being assessed with transcutaneous O2 and CO2 monitoring. Compared with conventional arterial blood gas values, those for transcutaneous oxygen (PtcO2) and transcutaneous carbon dioxide (PtcCO2) would likely be:

Direct measurement of arterial blood gases is the standard for monitoring arterial oxygen and carbon dioxide levels but only provides values for a specific point in time. Transcutaneous noninvasive measurements (Ptc) for oxygen (PtcO2) and carbon dioxide (PtcCO2) are based on diffusion of O2 and CO2 through the skin. In order to get reliable transcutaneous readings, the skin must be warmed to facilitate gas diffusion. This however allows for the metabolism of some oxygen and production of carbon dioxide by the skin The net result is a lower PtcO2 level and a higher PtcCO2 level

Ventilator Alarms

Disconnect alarms: low PIP, low TV, or low ETCO2 High PIP, high PEEP, sustained airway pressure, negative pressure and low O2

During a laparoscopic cholecystectomy on a 31 year old female, her oxygen saturation drops from 99% to 88%. Doubling the partial pressure of oxygen delivered to the patient will increase the concentration of dissolved oxygen in the blood by what percent? Select one: a. 50% b. 100% c. 150% d. 200% e. 500%

Doubling the partial pressure of a gas will in turn double its concentration in solution (a 100% increase). The principles of Henrys Law are used daily in anesthesia. It is the law that governs the idea that increasing the concentration of volatile anesthetic, which in turn increases its partial pressure, increases the concentration of anesthetic in the blood stream causing a deeper state of anesthesia. The relationship between the concentration of a gas in solution and the partial pressure of the gas is directly proportional. Henrys Law can be described as an equation. Cx = K X Px where Cx is gas concentration in solution, K is the gas solubility coefficient, and Px is the gas partial pressure. Divers often experience the diving sickness called the bends (or decompression sickness) which occurs when dissolved nitrogen concentrations in the tissue increase with the increased pressure associated with underwater diving. If the diver comes back to the surface too quickly, the nitrogen comes out of solution rapidly causing gas bubbles to form in the tissues making the diver sick. Thus, a diver must ascend slowly allowing the nitrogen to slowly come out of solution and be exhaled. If, however, prevention is impossible or fails, the treatment for the bends is hyperbaric oxygen. Important to note are the gas solubility coefficients of oxygen and carbon dioxide at body temperature (37 C) which are 0.003 mL/dL/mm Hg and 0.067 mL/dL/mm Hg, respectively. The solubility coefficient for oxygen is extremely small. This means that very little oxygen is dissolved in blood. Thus, a more efficient way for blood to carry oxygen is necessary. Hence the existence of hemoglobin. The correct answer is: 100%

During surgery for a tracheostomy tube, electrocautery ignites ventilation gas and causes a flash fire. What is the first intervention that you must immediately take? Select one: a. Shut off flow of all gases b. Turn from mechanical ventilator mode to hand bag c. Remove endotracheal tube d. Switch from oxygen to air with a flow of at least 1 liter per minute e. Apply water to endotracheal tube and into hypopharynx

During a flash fire of the airway, immediate removal of the endotracheal tube or airway device is indicated. Electrocautery or laser surgical devices may ignite combustible materials in the presence of oxygen. The risk is increased in superoxygenated environments and thus it is preferable to reduce oxygen concentrations to as low as the patient will tolerate, preferably close to room air concentrations (or at least below 0.30 FiO2). Other ways to reduce risk includes to withhold ventilation during cautery and to use an foil-wrapped tubes during operations where a laser may be in operation or filling the endotracheal tube cuff with saline. If the tube does ignite, the first action is to remove the endotracheal tube and ventilate the patient using a mask or via the tracheostomy if one can be rapidly placed. After a fire has occured, switching to room air concentration will not snuff out the fire and is an inappropriate and unbeneficial action to take. Water should not be poured into the oropharynx or down the endotracheal tube, which should be removed immediately. Turning off mechanical ventilation will be done after removal of the airway which should be immediate to remove a burning fuel source. Turning all airway gases off may sound like it will deprive the fire of oxygen or combustion supporting gas, but the amount of oxygen and gas already present and available in the lungs and airway tracts is sufficient enough to continue burning for some time and thus the airway itself has to be removed first. The correct answer is: Remove endotracheal tube

What does temperature compensation mean?

During vaporization the liquid anesthetic will cool, drawing heat from the metal of the vaporizer, which draws heat from the operating room. As liquid anesthetic cools, the saturated vapor pressure decreases, as does vaporizer output. Temperature compensation means the vaporizer has mechanisms for adjusting the output to compensate for temperature

What is the dye dilution method for estimating CO?

Dye injected through central line and measured through arterial line Area under dye indicator curve correlated with CO

A mixture of 1% isoflurane, 70% N2O, and 30% O2 is administered to a patient for 30 minutes. The expired isoflurane concentration measured is 1%. N2O is shut off, and a mixture of 30% O2 and 70% N2 with 1% isoflurane is administered. The expired isoflurane concentration is measured 1 minute after the start of this new mixture is 2.3%. The best explanation for this observation is

Effect of N2O solubility in Isoflurane Vaporizer output can be affected by the composition of the carrier gas used to vaporize the volatile agent in the vaporizing chamber, especially when N2O is either initiated or discontinued. This observation can be explained by the solubility of N2O in the volatile agent. When N2O and oxygen enter to vaporizing chamber, a portion of the N2O dissolves in the liquid agent. Thus the vaporizer output transiently decreases. Conversely, when N2O is withdrawn as part of the carrier gas, the N2O dissolved in the volatile agent comes out of solution, thereby transiently increasing the vaporizer output.

Somatosensory Evoked Potentials

Electrical stimulation to sensory nerve transmitted to cortex and measured by scalp electrodes Latency and amplitude are measured Affected by volatiles, etomidate, ketamine

When ECG electrodes are placed for a patient undergoing a MRI scan, which of the following is true? Electrodes should be as close as possible and in the periphery of the magnetic field Electrodes should be as close as possible and in the center of the magnetic field Placement of electrodes relative to the field is not important as long as they are far apart ECG cannot be monitored during MRI scan

Electrodes should be as close as possible and in the center of the magnetic field ECG monitoring is often not used during MRI scans because artifacts are very common (abnormalities in T waves and ST waves), and heating of the wires during the scan would potentially burn the patient. However, ECG can be used if the electrodes are placed close together and toward the center of the magnetic field and the wires are insulated from the patient's skin and straight. In addition, the wires should not be wound together in loops (because this can induce heating of the wires), and worn or frayed wires should not be used.

A patient has evidence on ECG of an acute inferior myocardial infarction. What associated findings should you look for?

Evidence of right ventricular involvement. Since V1 is really a right-sided lead. ST elevation in V1 accompanying an inferior MI suggest RV involvement. Alternatively you may check right-sided leads over the right precordium. ST elevation of 1 mm in right sided V4 or V5 indicated RV infarction Evidence of lateral wall involvement usually suggested by ST elevation in V5-V6 Evidence of posterior wall involvement as suggested by an R wave in V1 that is broad and/or tall, particularly in comparison with prior ECGs. Patients with posterior MI often have ST depression in V1-V2 Evidence of bradycardia caused by the SA or AV nodal block. Patients with inferior MI may require atropine and/or temporary pacing

Sources of signal degradation in an A-line

Excess tubing length, too thing tubing (rapid frequency response & decrease in damping ratio with ringing in arterial line) Wide, soft tubing, air bubbles (overdamping)

All anesthesia machines approved for current use have check valves located at the

Expiratory connection on the circle system Unidirectional check valves are required on the inspiratory and expiratory connections on the circle system to prevent rebreathing of exhaled gas. Some anesthesia machines have check valves at the common gas outlet or at vaporizer outlets, but they are not necessary

Oxygen pressure-failure devices and oxygen flush valves

Fail safe- nitrous oxide closed when O2 drops below 25 psi Oxygen flush valve- 35-75 L/min O2 goes straight to common gas outlet, bypassing flowmeters and vaporizers--potential for barotrauma depending on machine design

If the oxygen cylinder were being used as the source of oxygen at a remote anesthetizing location and the oxygen flush valve on an anesthesia machine were pressed down, as during an emergency situation, each of the items below would be bypassed by 100% O2 except O2 flowmeter first-stage regulator vaporizer check valve vaporizers

First stage regulator Anesthesia workstations have high-pressure, intermediate pressure, and low-pressure circuits. The high pressure circuit is from the oxygen cylinder to the oxygen pressure regulator (first stage regulator), which takes the oxygen pressure form a high of 2200 psi to 45 psi. The intermediate pressure circuit consists of the pipline pressure of about 50-55 psi and goes to the second stage regulator, which then lowers the pressure to 14-26 mm Hg. The low pressure circuit then consists of the flow tubes, vaporizer manifold, vaporizers, and vaporizer check valve to the common gas outlet The oxygen flush valve is in the intermediate pressure circuit and bypasses the low pressure circuit

What are the diagnostic criteria for myocardial ischemia?

Flat or downsloping ST-segment depression exceeding 1 mm read 60-80 msec after the J point (which is at the end of the QRS)

Flow volume loops (true learn)

Flow volume loops, aka spirometry, are a fundamental component of pulmonary function testing and allow for the assessment of both obstructive and restrictive lung disease. Small airway obstruction is evidenced by a loss of FEV1 greater than loss of FVC. A ratio of FEV1 to FVC of less than 80% is considered diagnostic for obstructive lung disease. This finding correlates to an early collapse of small airways and a prolonged expiratory phase due to air trapping. If there is evidence of obstructive lung disease a bronchodilator will be administered and the test repeated to assess for normalization. In syndromes such as exercise induced asthma, the patient may generate baseline flow/volume loops and then be asked to run on a treadmill or be administered methacholine to assess for the onset of bronchospasm and small airway obstruction Restrictive lung disease is primarily characterized by a loss of FVC with a proportional loss of FEV1 due to decreased total volume of air that is moving A variable extrathoracic obstruction (eg vocal cord dysfunction) results in a flattening of the inspiratory limb as flow during the inspiratory phase is limited. As air is pulled past the extrathoracic variable obstruction, the venturi effect causes a decrease in local pressure as the air flows past the obstruction resulting in airway collapse and flow limitation. A variable intrathoracic obstruction (eg tracheomalacia) will result in an expiratory flow limitation and flattening of the expiratory limb. The positive pleural pressure required to push air out of the lungs results in a collapse of the airways, and worsening of any intrathoracic obstruction and flow limitation. Extrathoracic obstructions tend to be dilated during the expiratory phase as air within the lung is being pushed past them. This tends to stent open any extrathoracic obstruction

Indications for Central line

Fluid management, TPN, infusion of drugs, aspiration of air emboli, insertion of transcutaneous pacing leads

Oxygen analyzers

Galvanic cell (fuel cell) and clark electrode (polarographic cell) Both contain cathode and anode electrodes in electrolyte gel separated by oxygen permeable membrane, current generated is proportional to oxygen partial pressure Clark electrode responds faster and external power source

Clinical considerations of pulse oximetry

Generally a SaO2 of 90% indicates a PaO2 of less than 65 mm Hg Carboxyhemoglobin (COHb) produces falsely high SaO2 because it absorbs @ same frequencies as HbO2 Methemoglobinemia produces SaO2 reading of 85% because it absorbs equally at both frequencies

Mixed venous oxygen saturation (SvO2)

Gives an indication of tissue oxygenation Normal SvO2 is 75% (range 60-80%) Higher under anesthesia up to 90%

Clinical considerations for ETCO2 analysis

Gradient between ETCO2 and PaCO2 is usually 2-5 mm Hg Abnormal waveforms COPD- upsloping expiration with no plateau reached spontaneous efforts- dip in plateau increased inspired CO2- baseline does not return to normal (zero)

what color is a CO2 tank

Gray

The more distal from the heart arterial BP is monitored makes for

HIGHER systolic pressures

HIGH SEA

Halothane and Isoflurane have similar vapor pressures (244 & 240 respectively) have HIGHER vapor pressures than sevoflurane and enflurane Remember! If you fill a vaporizer with an agent having a lower vapor pressure, then the delivered concentration will be lower than the dial setting If you fill a vaporizer with an agent having a HIGHER vapor pressure then the delivered concentration will be higher

How is a heliox mixture helpfuL?

Heliox mixture is extremely helpful for turbulent flow as is present in upper airway obstruction. If a pt is intubated this will not likely help Laminar flow depends on viscosity Turbulent flow depends on density

EKG high frequency filters

Help minimize distortion from muscle fasciculation, tremors, or electrical equipment

Causes of INC PIP & Unchanged Plateau pressure

INC inspiratory gas flow rate INC airway resistance (DEC dynamic compliance) Mechanical causes: -Kinked airway device (ETT) - Airway compression - Foreign body aspiration - Vocal cord paralysis -Endotracheal/endobronchial mass Physiologic causes: -bronchospasm -secretions

Causes of INC PIP AND Plateau pressure

INC tidal volume DEC chest/pulmonary compliance (increased static compliance) Above the diaphragm: - pulmonary edema - pleural effusion -tension pneumothorax -endobronchial intubation -Pneumonia Below the diaphragm: -Intra-abdominal packing/insufflation -T-Burg -Ascites

Mechanics of a-line transducer system

Ideal system has a frequency response > 25-40 Hz Short, rigid tubing with incompressible fluid (saline) typically used (DEC damping effect) Strain gauge attached to a diaphragm changes resistance with tension (pressure) Wheatstone bridge "amplifies" change in resistance and is callibrated High frequency of mech. system --> greater measurement accuracy Dense fluid raises frequency of system -->greater accuracy (saline better than air, blood better than saline)

Dessicated carbon dioxide absorbant can produce which of the following toxic gases when reacting with volatile anesthetics: Select one: a. Carbon monoxide b. Oxygen difluoride c. Phosphine d. Compound A e. Dihydrogen monoxide

If a ventilator is found producing gas flow for a significant period of time with no patient attached, you should change carbon dioxide absorbers to prevent production of carbon monoxide. The concern with leaving gas flows on over a prolonged period of time is that dessication, drying, of the carbon dioxide absorber may occur. A dessicated CO2 absorber is a known factor in producing carbon monoxide. This is due to the fact that soda lime and Baralyme absorbers contain strong bases that can create CO by extracting protons from anesthetic molecules. Other things that increase production of CO and carboxyhemoglobin are absorbent dryness, type of absorbent use, increased anesthetic concentration and temperature, and the use of low gas flows. Desflurane will produce the most carbon monoxide in dessicated soda lime and Baralyme, with sevoflurane producing the very least amount of carbon monoxide. Phosphine is a gas most notorious for being a product in methamphetamine manufacturing process. As a flammable and explosive gas it is a frequent cause of methamphetamine lab explosions, and the gas itself is highly toxic. Dihydrogen monoxide is another name for water often used as a hoax on people who don't recognize the chemical name as such. Not knowing chemistry can lead to fun events, such as water almost being banned in Aliso Viejo, California The correct answer is: Carbon monoxide

What are the characteristics of a left-bundle branch block?

In V1 there is a broad, deep S (or QS wave), with ST segment elevation, that may be preceded by a very narrow R wave In lead I there is a broad R wave (sometimes notched) without a Q or S wave

How does the CVP waveform change with atrial fibrillation?

In atrial fibrillation, a waves will be absent

How does the CVP waveform change with cardiac tamponade?

In cardiac tamponade all pressure will be elevated and the y descent will be nearly absent

Pulsed Doppler

In contrast to continuous wave doppler, which records the signal along the entire length of the ultrasound beam, pulsed wave doppler permits sampling of blood flow velocities from a specific region, known as the sample volume. This modality is particularly useful for assessing the relatively low velocity flows associated with transmitral or transtricuspid blood flow, pulmonary venous flow, and left atrial appendage flow. To permit this, a pulse of ultrasound is transmitted by a single piezoelectric crystal, and the receiver "listens" during a subsequent interval defined by the distance from the transmitter and the sample site. This transducer mode of transmit-wait-receive is repeated an an interval termed the pulse repetition frequency. The PRF is therefore depth dependent, being greater for near regions and lower for distant or deeper regions. The position of the sample volume is varied by adjusting the length of the transducer "receive" interval. In contrast to continuous wave doppler, which is sometimes performed without 2d guidance, pulsed doppler is always performed with 2D guidance to determine the sample volume position. Because pulsed wave doppler echo repeatedly sampled the returning signal, there is a maximum limit to the frequency shift or velocity that can be measured unambiguously. Thus the maximum detectable frequency shift, or Nyquist limit, is one half of the PRF. If the velocity of interest exceeds the Nyquist limit, "wraparound" of the signal occurs, first into the reverse channel and then back to the forward channel; this is known as aliasing

Causes of low mixed venous oxygen

Low O2 delivery: Hypoxia Anemia DEC cardiac output Alkalosis Methemoglobinemia INC O2 use: Fever INC metabolic states Shivering

How does the CVP waveform change with tricuspid regurgitation?

In tricuspid regurgitation, the c wave and x descent will be replaced by a large positive wave of regurgitation as the blood flows back into the right atrium during ventricular contraction. This can elevate mean CVP, but it is not an accurate measurement. A better way of estimating CVP in this case would be to look at the pressure between the regurgitation waves

What are risks of central line insertion?

Infection, air or thrombus embolism, dysrhythmias, hematoma, pneumothorax, hemothorax, cardiac perforation, cardiac tamponade, trauma to nearby nerves and thrombosis

Infrared spectroscopy for anesthetic gas analysis

Infrared absorption is measured, but unable to measure oxygen concentration

Which of the following combinations would result in delivery of a lower-than-expected concentration of volatile anesthetic to the patient? Sevoflurane vaporizer filled with Desflurane Isoflurane vaporizer filled with sevoflurane Sevoflurane vaporizer filled with Isoflurane All of the above would result in less than the dialed concentration

Isoflurane vaporizer filled with sevoflurane Saturated vapor pressures depend on the physical properties of the liquid and the temperature. Vapor pressures are independent of barometric pressures. At 20C the vapor pressures of halothane (243 mm Hg) and isoflurane (240 mm Hg) are similar, and at 1 atm the concentration in the vaporizer for these drugs is 240/760, or about 32%. Similarly, the vapor pressures of sevoflurane (160 mm Hg) and enflurane (172 mm Hg) are similar, and at 1 atm the concentration in the vaporizer for these drugs is 160/760, or about 21%. If desflurane (VP 669 mm Hg) is placed in a 1 atm pressure vaporizer, the concentration would . be 669/760, or about 88% Because the bypass flow is adjusted for each vaporizer, putting a volatile anesthetic with a higher saturated vapor pressure would lead to higher than expected concentration of anesthetic delivered to the vaporizer Putting a drug with lower saturated vapor pressure would lead to a lower than expected concentration of drug delivered from the vaporizer.

Underground power and protection from electric shock

Isolation transformer: isolates OR power supply from ground potential (i.e. OR power supply is ungrounded) If live wire contacts grounded pt, isolation transformer prevents current flow to pt Building regulations may no longer require ORs to have isolated power systems

What is the treatment for methemoglobinemia?

It is associated with benzocaine Administer methylene blue

Why is it important to zero the transducer system with a reference point at the approximate level of the heart?

It is important to zero the electromechanical transducer system with the reference point at the approximate level of the heart. This will eliminate the effect of the fluid column of the transducer on the arterial BP reading system. What happens if the arm is raised? The BP expressed by the arterial line will remain accurate provided that the stopcock remains at the wrist and the transducer is not moved once zeroed Raising the arm decreases the BP in the wrist but increases the pressure on the transducer by the same amount.

Is electrocardiography sensitive or insensitive for detecting chamber enlargement and hypertrophy?

It is insensitive. When echocardiography or autopsy is used as the gold standard, ECG misses many patients with real chamber enlargement or hypertrophy. This is particularly true with patients who have less severe (yet still potentially meaningful) degrees of these findings

Causes of high mixed venous O2 saturation

Low O2 use: CN poisoning Hypothermia Other: Impaired O2 tissue delivery (sepsis, burns) Mitral regurg

A manufacturing error allows for an empty isoflurane vaporizer to be accidently refilled with sevoflurane. A 35 year old healthy patient weighing 90 kg is induced with 50 mcg fentanyl, 100 mg of lidocaine, 200 mg propofol, and 100 mg succinylcholine. The endotracheal tube is placed without difficultly and the circuit is connected with 100% O2 and the isoflurane vaporizer set to 2% flowing at 5 L/min. Which of the following events is likely to occur 10 minutes later? Select one: a. The surgeon complains that the patient is moving after incision b. After incision, the patient remains still but shows an increased heart rate and blood pressure c. The patient remains stable despite surgical incision d. The patient's blood pressure decreases significantly causing severe hypotension requiring treatment with 200 mcg phenylephrine

It is likely that the surgeon with complain about patient movement with incision due to inadequate volatile agent concentration. In this scenario, you are administering sevoflurane with a vaporizer calibrated for isoflurane. Sevoflurane has a lower vapor pressure (160 mm Hg) than isoflurane (240 mm Hg). Therefore, in a variable bypass vaporizer, less fresh gas flow must be diverted into the vaporizer chamber to reach 2% isoflurane than must be diverted to reach 2% sevoflurane. Therefore, the actual concentration of sevoflurane delivered by an isoflurane vaporizer will be LESS than the dial setting because LESS fresh gas flow is diverted into the chamber. In this case, the concentration of sevoflurane being delivered to the patient is about 1.3% (see the calculation below). This is significantly below the minimum alveolar concentration required to keep a patient asleep during surgical incision. In summary, if you fill a vaporizer with an agent having a LOWER vapor pressure, then the delivered concentration will be LOWER than the dial setting. In contrast, if you fill a vaporizer with an agent having a HIGHER vapor pressure, then the delivered concentration will be HIGHER than the setting. Recall this useful equation for calculating splitting ratios: Flow through vaporizing chamber = Total FGF X [(agent concentration/100)/(Sat VP/Atm P)] This equation can be utilized to calculate the actual concentration in one of these scenarios. For a vaporizer calibrated for isoflurane, a dial setting at 2% with a FGF at 5 L/min would divert 0.317 L/min through the vaporizing chamber: Flow through vaporizing chamber ISO = 5 L/min X [(2/100)/(240/760)] = 0.317 L/min So 0.317 L/min of gas flow will flow through the vaporizer, but the vaporizer contains sevoflurane, not isoflurane. Thus, the vapor pressure will be different. Rearranging the equation to solve for agent concentration gives the following equation: Agent concentration = (vaporizing chamber flow/total FGF) X (Sat VP/Atm P) X 100% Agent concentration = (0.317 L/min/5 L/min) X (160/760) X 100% = 1.3% sevoflurane That was a lot of work. Luckily there is a shortcut. Forget about calculating the splitting ratio. Here is the simplified calculation: Actual Agent B concentration = Dial setting X (Agent B VP/Agent A VP) Agent A is the volatile anesthetic for which the vaporizer is calibrated, whereas Agent B is the volatile anesthetic that was used during the incorrect filling. So, in the above scenario, the simplified calculation would be: Actual sevo conc = 2% X (160 mm Hg/240 mm Hg) = 1.3% sevo The correct answer is: The surgeon complains that the patient is moving after incision

Ventilator Hazards

Leaks and disconnects: connection sites (esp at Y piece connector) loose or cracked bellows; incompetent system components (e.g. scavenger system or pop-off valve) Detection: ETCO2 monitor is the most sensitive (DEC ETCO2 or no ETCO2) human observation APL and respiratory volume monitors set proper high/low values Excessive positive pressure: INC risk of barotrauma - Oxygen flush during inhalation: scavenger spill valve closed -Obstructed scavenger system: kinked hose or stuck spill valve -hole in bellows: delivery of high driving gas pressures to the patient -Ventilator stuck in inspiratory mode Excessive negative pressure -excessive suction on scavenging system -naso or orogastric suction catheter in trachea -rapid descent of hanging bellows Machine set and delivered TV discrepancies -Leaks, breathing circuit compliance, gas compression, ventilator-FGF coupling (high FGF can INC TV above setting, INC MV, INC PIPs) No flow states: -Disconnect or obstruction of ETT or circuit tubing -Loss of pipeline and cylinder sources -Misconnection of ventilator hose to non-gas source -Ball type PEEP valve in inspiratory limb

Left shift Hb-O2 dissociation curve

Left shift results in higher affinity Hb-O2 Offloading of O2 is inhibited Causes: DEC temp Alkalosis (Bohrn effect) DEC CO2 DEC 2,3-DPG Fetal Hb Carbon monoxide Methemoglobinemia

why do we monitor lead V5?

Lies over 5th intercostal space and anterior axillary line- Anterior wall and lateral wall ischemia are easily seen

Filter color for argon or krypton laser light

Light amber-orange filters

Nitrous Oxide Cylinders

Liquid at room temp (critical temp is 36.5)--because this is above room temp, it can be kept liquified without an elaborate refrigeration system Because N2O is in the liquid state the volume remaining in the cylinder is not proportional to cylinder pressure E cylinder: 745 psi, 1590 L H cylinder: 15,900 L Pressure constant until 400 L remains (~25% is left) BLUE Must weigh cylinder to determine volume Energy is consumed in conversion of a liquid to a gas (latent heat of vaporization) -->there may be frost on the tank

Overdampened Waveform

Lose high-frequency waveform Systolic UNDERestimated

Jackson-Rees system is also known as

Mapleson F

The typical automatic noninvasive blood pressure measuring device most accurately determines

Mean arterial pressure Automatic noninvasive blood pressure devices use oscillometry and directly measure mean arterial pressure that is the pressure at which the cuff pressure fluctuations are maximal. Each manufacturer employs its own and unique algorithm to estimate systolic and diastolic pressures. These devices do not listen for Korotkoff sounds

What is thoracic bioimpedance?

Measures changes in thoracic volume to determine SV and thus CO can be determined

EEG

Measures electrical potentials generated by cells in cerebral cortex

What is joint cement and how does it cause hypotension?

Methymethacrylate, a cement used in joint replacement, undergoes an exothermic reaction that causes it to adhere to imperfections in the bony surface. Hypotension usually occurs 30-60 seconds after placement of the cement but can occur up to ten minutes later. Postulated mechanisms include tissue damage from the reaction, release of vasoactive substances when it is hydrolyzed to methacrylate acid, embolization, and vasodilation caused by absorption of the volatile monomer.

What amperage of microshock can lead to fatal injury: Select one: a. 10 microamps b. 100 microamps c. 1 milliamps d. 10 milliamps e. 100 milliamps

Microshock as low as 100 microamps can lead to fatal injury. Microshock is electrical current applied directly to or in direct proximity to the myocardial muscle. Macroshock, applied to the surface of the skin after you touch an electrical source, requires at a minimum 100 milliamps to lead to ventricular fibrillation. The allowable current leakage in the operating room is less than 10 microamps, well below what could lead to even a microshock causing significant injury. The correct answer is: 100 microamps

What are some causes for PAOP to be greater than LVEDP?

Mitral stenosis Left atrial myxoma Pulmonary venous obstruction Elevated alveolar pressure

Bain Circuit

Modification of Mapelson D Fresh gas supply runs coaxially inside corrugated expiratory tubing Advantages: compact, portable, easy scavenging, exhaled gases warm inhaled gases Disadvantages: risk of kinking/disconnect of coaxial tubing (i.e. fresh gas inlet)

Line Isolation Monitors

Monitors the degree of isolation between the power lines and the ground Alarm sounds if unacceptable current flow (>5 mA) to ground becomes possible --> unplug most recently plugged in piece of equipment Alarm does NOT interrupt power unless ground leakage circuit breaker activated LIMs PROTECT AGAINST MACROSHOCK BUT NOT MICROSHOCK (risk of microshock is decreased by grounded eqiupment i.e ground wire)

On a Monday morning the absorbent granules in your anesthesia machine, which was not used in the last 48 hours, are violet. In addition to rebreathing CO2 when exhausted, this form of absorbent also carries the risk of

Most anesthesia machines have a circle absorption system, which includes a canister of carbon dioxide absorbent that can effectively absorb exhaled CO2. This allows the anesthesia machines to use lower FGF, decreasing the amount of expensive inhaled anesthetic used. CO2 absorbents used the principle of neutralizing an acid (CO2 + H2O = carbonic acid H2CO3) with a base (mostly calcium hydroxide = Ca(OH)2. Some natural hydration of the granules is essential to allow the chemical reactions to occur. The end product of the reaction is calcium carbonate, water, and heat H2CO3 + Ca(OH)2 produces calcium carbonate (CaCO3) + H20 +heat Soda lime contains 76-81% Ca(OH02, 14-19% H2O 4% KOH 1% KOH NaOH and KOH serve as an effective catalyst for the chemical reactions to occur. Unfortunately, these catalysts degrade sevoflurane to the nephrotoxic called compound A, and degrade desflurane as well as isoflurane to CO when the granules are desiccated. The catalyst used in Amsorb Plus and Litholyme does not degrade sevo to compound A and does not produce CO from volatile anesthetics when volatiles are desiccated. The indicator dye used in soda lime that changes from off-white to violet can change back to the original white color when granules dry. In contrast, the indicator dye for Amsorb Plus and Litholyme changes from off-white to violet but does not change back to off-white. The absorptive capacity of Litholyme is similar to soda lime and slightly better than Amsorb Plus. In addition there is less heat produced with the chemical reaction in Amsorb Plus and Litholyme compared with soda lime Channeling can occur with any absorbent type, frank fire has only been reported with Baralyme which is no longer available.

General ventilator principles

Most bellows are pneumatically driven by O2 (double circuit ventilators) Driving gas circuit: provides driving force for ventilator, bellows and machine Pt gas circuit: gas supply to patient Inspiration: pressurized O2 from driving circuit fills space inside rigid container containing rigid bellows--bellows empty -Inspiratory time: based on set TV, inspiratory flow, and RR -Termination of inhalation: time cycled and/or pressure limited Exhalation Ascending bellows: RISE during exhalation will not rise if circuit disconnect or leak Descending bellows: hang during exhalation fills by gravity even if disconnect or leak

What is the soda lime equation?

Most common absorbent: Ca(OH)2, H2O, NaOH, KOH

OR fires

Most common risk factor = open delivery of oxygen combustible supplies: ETTs, oxygen, surgical drapes, alcohol cleansing solutions flammable substances may become explosive around O2 and N2O Fire triad: fuel, oxidizer, ignition

Circle system

Most commonly used/prevents rebreathing of exhaled CO2 - Reservoir bag: reserve gas volume - oxygen analyzer: measures inspired and expired O2 -APL/pop-off valve- can be adjusted to facilitate manual bag compressions to assist ventilation of pts lungs. Allows venting of excess gas to waste scavenging system Bag/ventilator switch: exclude/include reservoir bag and APL from system Inspiratory one way valve- open during inspiration and closed during expiration expiratory one way valve- open during expiration and closed during inspiration CO2 absorbent- removes CO2 from breathing circuit (chemical neutralization) Spirometer- measures exhaled TV and RR Circuit pressure gauge- measures circuit airway pressure in cm H2O

Mapleson D circuit

Most efficient for controlleD ventilation, most commonly used FGF forces alveolar gas away from pt and toward pressure release valve Dog Bites Can Ache

Mapleson A circuit

Most efficient for spontAneous ventilation FGF = Minute ventilation, which is sufficient to prevent CO2 rebreathing All Dogs Can Bite

An open waste gas scavenging system

Must be connected to a source of vacuum An open waste-gas scavenging system requires a reservoir but no valves. It must be connected to a source vacuum to actively withdraw waste gases. It is usually connected to both the APL and ventilator relief valves via a "Y" connector

How are patients with MI subdivided on the basis of ECG changes during infarction?

Myocardial infarctions are often divided into two types: ST segment elevation MI and non-ST segment elevation MI. Patients with ST segment elevation should be considered for immediate percutaneous coronary intervention (PCI) or thrombolytic therapy if PCI is unavailable. Q waves usually develop over time in the leads where there is elevation. Q waves may diminish in size or go away over time. Patients with acute MI without ST elevation often have ST segment depression (which may be dynamic) and/or T wave inversions. Patients with non-ST segment elevation MI can usually be made pain free with medical therapy and cardiac catheterization is often performed within several days.

Gases and vapors that may be measured by infrared spectrometry include all of the following except: halothane isoflurane carbon dioxide nitrogen nitrous oxide

N2O and all of the volatile anesthetics absorb infrared light. Nitrogen and oxygen may be determined by mass spectroscopy or Raman spectroscopy. Oxygen may also be measured by electrochemical or galvanic detectors

What is the second gas effect?

N2O diffuses much more rapidly into the blood from the lungs than volatile anesthetic agents. This quick diffusion results in decreased alveolar concentration of N2O in the lungs and increased concentration of remaining gases Concentrating the remaining gases including the volatile agent speeds induction Use of N2O also increases alveolar ventilation. Alveolar ventilation is inherently driven by gas diffusion across the alveolar membrane . As oxygen is dissolved in blood more air is pulled into the alveoli to replace the deficit. N2O diffuses into blood very quickly (1L/min) thus causing a large deficit and increasing flow of new gas into the alveoli

Of the following medical lasers, which laser light penetrates tissues the most? Argon laser Helium-neon laser Nd:YAG laser CO2 laser

Nd:YAG Laser refers to light amplification by the stimulated Emission of Radiation. Laser light differs from ordinary light in three main ways. First, laser light is monochromic (possesses one wavelength of color) Second, laser light is coherent (the photons oscillate in the same phase). Third, laser light is collimated (exists in a narrow parallel beam). Visible light has a wide spectrum of wavelengths in the 385-760 nm range. Argon laser light, which can penetrate tissues to a depth of 0.05-2 mm, is either blue (wavelength 488 mm) or green (wavelength 514 nm) and is often used for vascular pigmented lesions because it is intensively absorbed by hemoglobin Helium-neon laser light is red, has a frequency of 632 nm, and is often used as an aiming beam because it has very low power and presents no significant danger to OR personnel. Nd:YAG laser light is the most powerful medical laser and can penetrate tissues from 2-6 mm. Nd:YAG laser light is in the near infrared range, with a wavelength of 1064 nm., has general uses (prostate surgery, laryngeal papillomatosis, coagulation), and can be used with fiberoptics CO2 laser light is in the far infrared range, with a long wavelength of 10,600 nm. Because CO2 laser light penetrates tissues poorly, it can vaporize superficial tissues with little damage to underlying cells

Fresh Gas flow Decoupling

On most ventilators except older models Inspiration: FGF--reservoir bag Exhalation: Bellows refill from reservoir and FGF -FGF no longer influences TV

Does ST segment elevation always indicated a myocardial infarction?

No other causes include: Acute subepicardial injury Early repolarization pattern Pericarditis Hyperkalemia Hypercalcemia LVH LBBB Brugada syndrome Normal varient

Penaz (Finapres) BP

Noninvasive continuous finger arterial BP monitor based on vascular unloading technique, which involves an infrared plethysmograph mounted on an inflatable finger cuff. Finapres is the acronym for "finger arterial pressure"

Arterial tonometry

Noninvasive method for measuring BP in which a pressure transducer is placed over an artery. This method is less accurate for patients with peripheral artery disease

What is the most important feature of an anesthesia machine to prevent hypoxic gas mixture delivery?

O2 analyzer because it is the only machine monitor of low pressure system integrity downstream from flow meters

What physical law best relates flow to pressure gradient and resistance? Select one: a. Boyles law b. Charles' law c. Gay-Lussac's law d. Henry's law e. Ohm's law

Ohms law states that fluid flow (as a gas or liquid) equals the pressure gradient divided by resistance (Flow = ?P/R). Ohms law can be applied to both respiratory and cardiovascular physiology. The pressure gradient used for calculating respiratory airflow is the difference between atmospheric pressure and alveolar pressure (?P = Patm Palv). Thus, Ohms law adapted to the respiratory system can be written: Flow (V) = (Patm Palv)/R (Flow in reference to the respiratory system is denoted with the symbol, V) Ohms law applied to the cardiovascular system is written: Flow (Q) = (Pa-Pv)/R Where Pa = arterial pressure and Pv = venous pressure (Flow in reference to the cardiovascular system is denoted with the symbol, Q) Overall, the implications are the same. Raising the pressure gradient (or increasing the difference between pressures across a distance) will increase the flow through that distance. In contrast, raising the resistance will decrease flow. The correct answer is: Ohm's law

Why do all oxygen outlets and anesthesia machines come with a warning that says "use no oil"?

Oil placed near concentrated oxygen causes a great risk for fire Anesthesia machine provides a heat source that could be high enough to ignite a fire

PCAs (true learn)

Opioid PCAs have not been shown to decrease the cost of hospital admission, time to discharge, or incidence of opioid induced side effects when compared to traditional nurse administration dosing regimens Bottom line: PCAs provide superior pain control to traditional nurse administered "as needed" IV opioid dosing regimens, though they may increase the patients total opioid exposure during hospitalization

The dial of an isoflurane-specific, variable bypass, temperature-compensated, flowover, out-of-circuit vaporizer (i.e. modern vaporizer) is set on 2% and the infrared spectrometer measures 2% isoflurane vapor from the common gas outlet. The flowmeter is set at a rate of 700 mL/L during this measurement. The output measurements are repeated with the flowmeter set at 100 mL/L (vapor dial still set on 2%). How will these two measurements compare with the first measurement taken?

Output will be less than 2% in both cases The output of the vaporizer will be lower at flow rates less than 250 mL/min because there is insufficient pressure to advance the molecules of the volatile agent upward. At extremely high carrier gas flow rates (>15 L/min) there is insufficient mixing in the vaporizing chamber

Why are oxygen flowmeters positioned closest to the vaporizer and last in line from the other gases? Select one: a. To reduce risk of hypoxic mixture being delivered to patient b. To ensure proper vaporizer compensation of changes in ambient air pressure c. To prevent a hypoxic balance of volatile agent and oxygen d. To ensure a proper splitting ratio inside the vaporizer e. None of the above

Oxygen flowmeters are positioned closest to the vaporizer to reduce risk of hypoxic gas mixtures being delivered to patient. The safest position for the oxygen flowmeter is closest to the vaporizer. If other gases were downstream to the oxygen and a leak or blockage developed in or downstream of the oxygen flowmeter, the oxygen may not make it to the patient whereas other gases might. This could create a hypoxic situation for the patient. Thus, one of the safety systems of the ventilator is that oxygen's flowmeter is closest to the vaporizer. The correct answer is: To reduce risk of hypoxic mixture being delivered to patient

Paramagnetic oximetry

Oxygen is highly paramagnetic (6 unpaired electrons in outer shell). The device detects changes in sample line pressure resulting form the attraction of O2 by switched magnetic fields. The changes in pressure correlate with the oxygen concentration in the sample line. no calibration needed

Polarographic O2 analyzers

Oxygen passes permeable membrane for reaction: O2 + 2 H2O + 4 e- --> 4OH The current change is proportional to the number of oxygen molecules surrounding the electrode. Important for the anesthesia machine, along with arterial/venous blood gas analyzers. No calibration needed

Galvanic cell

Oxygen produces current after passing through permeable membrane into electrode (lead anode and gold cathode). The current is proportional to the partial pressure of oxygen in the fuel cell. Requires frequent calibration (as part of the daily machine check). No battery, although lifespan is ~ 1 year

Which of the following is NOT found in the low pressure circuit on an anesthesia machine? Oxygen supply failure alarm Flowmeters Vaporizers Vaporizer check valve

Oxygen supply failure alarm The anesthesia machine has two main pressure circuits. The higher pressure circuits consist of the gas supply from the pipelines and tanks, all piping, pressure gauges, pressure reduction regulators, check valves (which prevent backward gas flow), the oxygen pressure sensor shut off valve (also called the oxygen failure cutoff or fail-safe valve), the oxygen supply failure alarm, and the oxygen flush valve--or simplistically, everything up to the gas flow control valves, flowmeters, vaporizers, and vaporizer check valve and goes to the anesthesia machine common gas outlet.

Lambert-Beer Law as it pertains to pulse oximetry

Oxygenated and reduced Hb absorb light differently red & infrared freq Oxyhemoglobin absorbs more infrared 960 nm Deoxyhemoglobin absorbs more red light 660 nm Measures pulsatile arterial blood flow (identified by plethysmography)

PAOP usually estimates?

PAOP usually estimates LVEDP

SpO2 of 90% =

PaO2 60 mm Hg

SpO2 of 98% =

PaO2 90 mm Hg SpO2 readings <90% are inaccurate

How can you estimate PaO2?

PaO2 can be estimated by FiO2 x 5

What are the noninvasive methods of BP monitoring?

Palpation: inflate cuff and feet for return of distal pulse. Tends to underestimate systolic pressure. No DBP or MAP Doppler probe: inflate cuff and listen for return of flow. No DBP or MAP Auscultation: listen for Korotkoff sounds, auscultory gap in hypertensive pts Oscillometry: Max amplitude at MAP, onset at systole, end at diastole Plethysmography: finger cuff pressure required to maintain finger volume beat to beat Arterial tonometry: pressure required to flatten an artery over bone, beat to beat

Why do we monitor lead II?

Parallels atria Arrhythmias and Inferior wall ischemia are easily seen

Compare passive vs active waste gas scavenging

Passive--disposal tubing -- outside ventilation duct Active--disposal tubing-- hospital vacuum system

What are the characteristics of a right-bundle branch block?

Patients with RBBB typically have an rSR' pattern in V1 and a broad terminal S wave in I and V6

For patients with ST segment elevation MI, how is the location identified?

Patients with inferior MI generally have ST elevation in II, III, and aVF Lateral MI-I, aVL, V5, v6 Anterolateral- I, aVL, V3-V6 Septal MI- VI and V2 Anteroseptal- V1-V4 Anterior MI- V3-V4

How is peak pressure measured?

Peak pressure is measured during the delivery of airflow at the end of inspiration. It is influenced by the inflation volume, airway resistance, and elastic recoil of the lungs and chest wall and reflects dynamic compliance of the total respiratory system

PISS

Pin Index Safety System E-cylinders to machine

Why will exchanging an ETT from 6.5 to 8.0 decrease resistance to airflow and allow for the delivery of greater TV?

Poiseuille's Law: volume flow of a fluid through a rigid tube is directly proportional to the pressure gradient of the tube and the tube radius (to a power of four) and indirectly proportional to the length of the tube and viscosity of the fluid flowing through it

Higher vaporizer output than dial setting can be caused by: Select one: a. Gas flow at 15 L/min b. Using the oxygen flush valve c. Positive pressure ventilation d. Increased ambient temperature e. Low cardiac output

Positive pressure ventilation can cause higher output than dial setting by a pumping effect. While the pumping effect is not as prominent in modern vaporizers which have added safety features to prevent this phenomenon, older models do exhibit higher vaporizer output due to the back pressure caused by intermittent positive pressure ventilation. The theory is that the back pressure causes a compression of gas molecules in the vaporizer chamber that increases vapor concentration at the common gas outlet. Very high gas flows result in lower vaporizer output. Using the oxygen flush valve bypasses the flowmeters and vaporizers, thus diluting the volatile agent in the breathing circuit. While an increase in ambient temperature causes an increase in saturated vapor pressure which would increase vapor output, variable bypass vaporizers are equipped with a bimetallic strip which allows for temperature compensation. Finally, low cardiac output enhances gas uptake in the lungs but does not increase vaporizer output. The correct answer is: Positive pressure ventilation

Cardiac output is determined by what 4 main factors?

Preload, afterload, myocardial contractility, and heart rate

Leakage current

Present in all electrical equipment Usually less than 1 mA which is below the fibrillation threshold of 100 mA Microshock- shock directly on the heart, as low as 100 mA can be fatal Max leakage in OR is 10 microA

What is the purpose of the waste scavenging system?

Prevent OR pollution with anesthetic gases

What does the x descent represent on CVP waveform?

Probably caused by the downward movement of the ventricle during systolic contraction. Occurs BEFORE the T wave

A 59 year old pacemaker dependent patient comes to surgery with the pacemaker programed in the DDD mode. Extracorporeal shock wave lithotripsy (ESWL) is scheduled for fragmentation of several 3-5 mm kidney stones. What preparation is needed before undertaking ESWL in this setting to avoid inappropriate firing of the lithotripter?

Program pacemaker in VVI Lithotripsy is a noninvasive treatment using ultrasonic shock waves to break apart kidney stones. There are three main components of lithotripters: an energy source, a system to focus the shock wave, and fluoroscopy or ultrasound to visualize and localize the stone in focus. Because most lithotripters are triggered by the R wave of the ECG and can be fired inappropriately by the atrial-pacing artifact (with the potential of producing serious cardiac dysrhythmias), pacemakers should be changed to a mode that does not pace the atrium. Thus the lithotripter has no possibility of misinterpreting the atrial spike as an R wave. In addition, the shock waves can interfere with pacemaker function, and some devices can be damaged, so an alternative means of pacing should be available. After the lithotripter procedure, the pacemaker should be reactivated to the patient's original mode (in this case DDD) and checked for proper functioning. If the patient has an AICD, it needs to be turned off during the treatment and reactivated after the treatment

A patient with a prior history of awareness under anesthesia is to be monitored with a BIS monitor. This monitor most reliably indicates the depth of anesthesia when the patient is anesthetized with?

Propofol The BIS monitor has been validated primarily with anesthetic techniques based exclusively or primarily on propofol or volatile anesthetics. It does not reliably indicate depth of anesthesia when the anesthetic technique is based exclusively or primarily on ketamine, N2O, xenon, or opioids

Why are the flowmeters for air, O2, and N2O arranged in a specific order?

Reasons include the US (NIOSH) government standards, manufacturer conventions, and safety. Requiring the O2 knob to be in the same relative position on all anesthesia machines decreases the risk of the anesthesiologist turning the wrong knob. In the US the O2 flowmeter must always be on the right, closest to the point of egress into the common gas manifold, just proximal to the anesthesia vaporizers. With the O2 flowmeter in that position, most leaks will tend to selectively loose gases other than O2. This configuration is least likely to deliver a hypoxic gas mixture. Again, the best way to detect a hypoxic gas mixture is through use of an oxygen analyzer

What is reciprocal change? Why is it important?

Reciprocal change is ST segment depression that occurs in patients with an ST elevation MI. For example, a patient with an inferior MI may have ST segment elevation in II, III, and aVF With ST depression (reciprocal change) in I and aVL Not all patients with ST elevation MI have reciprocal change, but when it is seen, it generally confirms the diagnosis of acute MI

Potassium titanyl phosphate: Nd:YAG laser light filter

Red filters

What is the Hb-O2 dissociation used for?

Relates % of Hb saturation to PaO2

Gay-Lussac's Law

Relates pressure with temperature where P1/T1 = P2/T2

Desflurane Vaporizer

Requires special heated vaporizer due to high vapor pressure Reservoir heated to 39 C No compensation for elevation Desflurane vapor pressure is high Tech 6 maintains constant reservoir of 2 atm regardless of ambient temp Shut off valve only opens when vaporizer is warmed up & concentration dial is on Higher altitudes = DEC partial pressure so INC concentration for same effect is needed

Right shift in Hb-O2 dissociation curve

Right shift results in peripheral offloading of O2 Causes: INC temp INC H+ (Bohr effect) INC CO2 INC 2,3-DPG Adult Hb

An adult has a large R wave in V1. What is the differential diagnosis?

Right ventricular hypertrophy (look for right axis deviation, right atrial enlargement, and right ventricular strain with ST-T abnormalities) Posterior myocardial infarction Wolff-Parkinson-White syndrome Muscular dystrophy Normal early transition

What is the thermodilution method of determining CO?

Room temp fluid is injected an temperature change of thermistor is inversely proportional to CO Must inject Fluid rapidly Modified method for continuous CO involves a thermal filament that heats blood and thermistor correlates change in blood temperature with CO

Raman spectroscopy for anesthetic gas analysis

Sample ionized by laser and intensity of light emitted as gas returns to unexcited state is measured

Mass spectrometer for anesthetic gas analysis

Sample is ionized and passed through a magnetic field

An elderly patient presents with fatigue, confusion, and atrial fibrillation with a slow ventricular response (HR=40). The ECG demonstrates ST depression that is concave upward. The family states that the patient is on an unknown medication that is locked in his apartment. What lab test should you order to confirm your suspicion?

Serum digoxin level

What ECG findings suggest hypercalcemia?

Short QT interval With or without ST segment elevation

Clark cell

Similar to galvanic cell. Oxygen produces current after passing permeable membrane (silver anode and platinum cathode) battery required.

Two hours into an L4-L5 TLIF, you note re-breathing of carbon dioxide on capnography. You further note the granules have changed color from white to purple to show exhaustion of absorbent properties. The most commonly used absorbent, soda lime, can absorb how much carbon dioxide? Select one: a. 13 liters per 10 grams of absorbent b. 130 liters per 10 grams of absorbent c. 10 liters per 100 grams of absorbent d. 23 liters per 100 grams of absorbent e. 230 liters per 100 grams of absorbent

Soda lime can absorb 14-23 liters for every 100 grams of absorbent, and barium hydroxide lime (BaraLyme) can absorb 9-18 liters of CO2 per 100 grams of absorbent. Carbon dioxide absorbents are designed to remove CO2 to prevent re-breathing of carbon dioxide which may lead to hypercapnia. Initially the patient's exhaled CO2 combines with water (there is additional water contained within the soda lime) to create carbonic acid. This carbonic acid enters the carbon dioxide absorbent canister and interacts with the soda lime (or other absorbent) producing water, heat, and calcium carbonate. Carbon dioxide absorbent also will absorb and re-release volatile anesthetic agent. The correct answer is: 23 liters per 100 grams of absorbent

The line isolation monitor

Sounds an alarm when grounding occurs in the OR The line isolation monitor gives an alarm when grounding occurs in the OR or when the maximum current that a short circuit could cause exceeds 2-5 mA. The line isolation monitor is purely a monitor and does not interrupt electric current. Therefore the line isolation monitor will not prevent microshock or macroshock

Filter color for Nd:YAG laser light

Special green tinted filters

Spirometers and breathing-circuit pressure gauges

Spirometer measures TV -Pneumotachography is a fixed orifice flowmeter that functions as a spirometer -Wright respirometer- expiratory limb, measures exhaled TV Breathing circuit pressure gauge - Usually between inspiratory and expiratory valves -Measures circuit airway pressure in cm H2O

Compare standing bellows to hanging bellows

Standing bellows are better (what we use) because they collapse if the circuit is disconnected (hanging bellows continue to fill--wont show us that something is wrong) Most bellows require oxygen to operate--keep in mind if gas system failure

Avogadro law

States that equal volumes of all gases at the same temperature and pressure will contain the same number of molecules

How is static pressure measured?

Static or plateau pressure is measured during an end-inspiratory pause, during a no-flow condition, and reflects the static compliance of the respiratory system, including the lung parenchyma, chest wall, and abdomen.

Sites for central line insertion

Subclavian: risk of pneumothorax and higher risk of infection long term Internal jugular: safe and more accessible --Left sided INC risk of vascular errosion, pleural effusion, and chylothorax

What is the best muscle group to monitor after administration of sux to see if the patient is ready for intubation?

Succinylchoine induced laryngeal relaxation is best monitored by observing response of adductor pollicis This is opposite of non-depolarizing relaxants which are best observed at orbicularis occuli muscle during intubation

Which of the following describes how surfactant changes the effect of Laplace's Law on lung mechanics: Select one: a. Surfactant increases elastic recoil, increasing FEV1 and allowing for easier exhalation b. Surfactant decreases surface tension, reducing the pressure within small alveoli c. Surfactant coats alveoli with an oil-like substance that assists with oxygen exchange d. Surfactant coats alveoli with an oil-like substance that assists with oxygen exchange e. Surfactant is produced by Type 2 alveolar cells

Surfactant decreases surface tension, reducing the pressure within small alveoli. Laplaces Law has applications in respiratory and cardiovascular physiology. In the context of alveoli, Laplaces Law can be written as: Pressure = (2 X surface tension)/radius. When comparing two bubbles of different sizes but with equal surface tension, the smaller bubble will have a greater pressure. Thus, alveoli that are smaller would tend to empty into larger alveoli. However, this does not occur due to a coating of surfactant within alveoli. The surfactant works by decreasing surface tension such that, as an alveolus gets smaller, the surfactant becomes more concentrated, decreasing surface tension further. This ensures equal pressure within all alveoli regardless of size. Prematurely delivered babies may have difficulty breathing due to underdeveloped lungs and a lack of surfactant which makes inhalation especially difficult. Think about blowing up a balloon. At first it takes a lot of pressure to begin inflation, but as the balloon gets larger, less pressure is needed to continue inflation and it becomes easier to blow up. A premature baby must overcome this initial resistance to inflation every breath. This is why "preemies" may spend their first few months on a ventilator. Laplaces Law can also be used to explain the mechanism of COPD caused by emphysema. In this disease, the alveolar walls are destroyed creating larger airways that are much easier to inflate because they are like halfway inflated balloons. However, the overinflated alveoli lack sufficient surface tension and elastic recoil to readily deflate. (Recall that exhalation is a passive process in a healthy individual.) Thus, exhalation becomes more difficult and lung volumes tend to increase due to air trapping. Chest x-rays of these patients show very large lungs. The other choices are incorrect as surfactant actually reduces elastic recoil and alveolar closing. Surface tension caused by the interaction of water molecules is the driving force behind elastic recoil. While surfactant indirectly assists with oxygen exchange by helping to keep alveoli open and available for the diffusion process, surfactant is not directly involved in the gas exchange process. Serous fluid, not surfactant, decreases friction in the pleural cavity. Finally, although it is true that type 2 alveolar cells produce surfactant, this choice does not answer the question that is asked. The correct answer is: Surfactant decreases surface tension, reducing the pressure within small alveoli

Ultrasonography and CO?

TEE/pulsed doppler

A patient with a right breast mass is administered endotracheal general anesthesia. 30 mg of atracurium is administered during induction, and now 45 minutes after administration the patient is prepared for extubation. Once alert, you ask the patient to lift their head for five seconds, which the patient successfully does. What percentage of receptors at the neuromuscular junction may still be blocked in this patient despite the successful head lift? Select one: a. 20 % b. 30 % c. 40 % d. 50 % e. 60 %

Tests such as a 5 second head lift and the ability to grip your hand for 5 seconds still allows that 50% of receptors may still be occupied. The correct answer is: 50 %

APL valve (true learn)

The APL valve is used to adjust the anesthesia machine circuit airway peak pressure when in manually assisted/spontaneous mode. It is isolated form the circuit when the anesthesia machine is placed in mechanical ventilation mode. The APL should remain fully open when the pt is breathing spontaneously. The APL must be closed in order to manually assist pt ventilation, and when performing the airway circuit leak test

At your new job at a hospital near the Florida coast you are asked to give a break in an operating room to one of your colleagues. The patient is a 78 year old female that is having a left total knee replacement. The patient weighs 65 kilograms and has no known drug allergies. She is receiving an FiO2 of 0.64 with an SaO2 100%, PaO2 285, PaCO2 40 and an Hgb of 12 mg/dL. What is the patient's PAO2? Select one: a. 406 mmHg b. 456 mmHg c. 370 mmHg d. 321 mmHg e. 295 mmHg

The PAO2 is 406 mmHg. In this case, the information about the Florida coast is given to let the student know that they are operating at or near sea level which has an atmospheric pressure of 760 mmHg. At normal body temperature, water vapor pressure is 47 mmHg. PIO2= (Atmospheric Pressure- Water Pressure) x FiO2 or (760-47) x 0.64 = 456.32 Now need to calculate PAO2 to get our answer. The formula for PAO2 is PAO2 = PIO2 - (PaCO2/RQ) RQ is usually 0.8 and should be assumed to be 0.8 unless indicated otherwise. PaCO2 on average is 40 mmHg and should be assumed that unless indicated otherwise. PAO2= 456.32 - (40/0.8)= 406.32 or 406 mmHg You can also estimate PAO2 by multiplying your FiO2 by 6. In this scenario it would be 64 x 6 = 384 mmHg. PaO2 can be estimated by FiO2 x 5. The correct answer is: 406 mmHg

What ECG findings suggest hypocalcemia?

The QT interval is prolonged without broadening of the T wave (in contrast to the situation with hypokalemia). The T wave appears to be pushed away from the QRS

A patient from the medical intensive care unit is brought to the operating room for rigid bronchoscopy with brushings. After induction, he is kept relaxed with a repeated dose of vecuronium. The procedure is uneventful, and he appears to be a candidate for extubation at the end of the case. When preparing to extubate, which of the following muscle groups is the best to monitor recovery from non-depolarizing neuromuscular blockade? Select one: a. Orbicularis oculi b. Adductor pollicis c. Posterior tibialis d. Abductor policis e. Extensor carpi radialis

The adductor pollicis is the best muscle response to monitor when trying to determine whether a patient has sufficient recovery of airway reflexes and muscle tone after non-depolarizing neuromuscular blockade. The adductor pollicis is innervated by the ulnar nerve and electrodes should be placed over this nerve to perform this test. The correct answer is: Adductor pollicis

After deep extubation of a 20 year old male, you notice no spontaneous movement of air and attempt to apply positive pressure ventilation by closing the APL valve and mask ventilating the patient. Choose the incorrect statement regarding the APL valve: Select one: a. The APL valve can be completely closed b. If too open, the APL valve can prevent delivery of manual ventilation c. An open APL valve may not prevent barotrauma from use of the oxygen flush valve d. The APL valve should be opened for spontaneous ventilation e. Excess gas is sent through the APL valve into the scavenging system

The adjustable pressure-limiting valve can not be completely closed to help decrease the likelihood of barotrauma Nonetheless, barotrauma may occur from high circuit pressures due to a maximally closed APL valve. The upper limit on a typical APL valve is 70 cmH2O. For spontaneous ventilation, the APL should be kept completely open. In order to manually ventilate or assist a patient's ventilation, the APL should be adjusted to provide the pressure to support the tidal volume but not such that gastric insufflation or barotrauma may occur. The correct answer is: The APL valve can be completely closed

A 72 y/o male is scheduled for a colon resection s/d to colon cancer. The patient has a significant history for coronary artery disease, hypertension, diabetes mellitus, morbid obesity, and hyperlipidemia. The patient weighs 139 kgs and his starting Hb is 13.2 g/dL. What is this patient's allowable blood loss? Select one: a. 2359 mL b. 2101 mL c. 2205 mL d. 1907 mL e. 1705 mL

The allowable blood loss is 2359 mL. ABL = EBV x ((Hborig-Hballow)/(Hborig)) EBV for an adult male = 70 mL/kg Hballow= 10 g/dL EBV = 70 mL/kg x 139 = 9730 mL ABL = 9730 x ((13.2-10)/(13.2)) = 2358.7 = 2359 With this patient's history we chose a transfusion trigger of 10 g/dL. Given the size of this patient, large blood volume and extensive history it is imperative to be vigilant of all fluid ins and outs and hemodynamic parameters. Even though 10 g/dL has been chosen as the transfusion trigger you may need to transfuse earlier if the patient shows signs of decompensation. It is always important to discuss with the anesthesia and surgical team of what the transfusion trigger will be. You always want to notify the anesthesia and surgical teams before transfusing the patient. In any case that you expect high volume shifts and blood loss always know your ABL and tranfusion trigger. The correct answer is: 2359 mL

Uptake of sevoflurane from the lungs during the first minute of general anesthesia is 50 mL. How much sevoflurane would be taken up from the lungs between the 16th and 36th minute?

The amount of volatile anesthetic taken up by the patient in the first minute is equal to the amount taken up between the squares of any two consecutive minutes (square root of time equation). Thus, if 50 mL is taken up in the first minute, 50 mL will be taken up between the first (1 squared) and fourth (2 squared) minutes. Similarly, between the fourth and ninth minutes (2 squared and 3 squared), another 50 mL will be absorbed. In this example, we are looking for the uptake between the 16th (4 squared) and 36th (6 squared) minutes, which would be 2 consecutive minutes squared or 2 x 50 mL = 100 mL

What is the average adult VCO2 in mL/min? Select one: a. 100 ml/min b. 200 ml/min c. 250 ml/min d. 300 ml/min e. 350 ml/min

The average adult VCO2 is 200 mL/min. The average VCO2 value is based on a 70 kg patient using the equation: VCO2 = weight in kg^0.75 * 8 The correct answer is: 200 ml/min

What is true about blood pressure cuffs?

The bladder length should be at least 80% and the width 40% of the limb circumference. If the bladder is too small, a larger pressure will be needed to occlude flow and erroneously high blood pressure reading will result. The labeling of a cuff as "adult" or "thigh" is a general guideline; the cuff size should be chosen to match a particular limb size regardless of whether the limb is the arm or the leg

If a patient has a blood pressure of 125/84, heart rate of 80, stroke volume of 60 mL, and a CVP of 3. What is the calculated systemic vascular resistance? Select one: a. 1580 dynes/sec/cm5 b. 1630 dynes/sec/cm5 c. 2030 dynes/sec/cm5 d. 1350 dynes/sec/cm5 e. 1780 dynes/sec/cm5

The calculated systemic vascular resistance is 1580 dynes/sec/cm5. SVR= ((MAP-CVP)/(CO)) x 80 with the average being 1900-2100 dynes/sec/cm5 (MAP is mean arterial pressure, CVP is central venous pressure, CO is cardiac output) MAP = ((Diastolic x 2) + (Systolic))/3 = (168+ 125)/3= 97.67 mmHg CO = HR x SV = 80 x 60 = 4.8 (HR is heart rate, SV is stroke volume which is 60 mL in the question) CVP = 3 as given in the question Thus, SVR = ((97.67-3)/(4.8)) x 80 = 1577.83 dynes/sec/cm5 The correct answer is: 1580 dynes/sec/cm5

Describe latent heat of vaporization in terms of desflurane vaporizer

The concept of latent heat of vaporization explains why desflurane requires a special ventilator Latent heat of vaporization: the energy consumed as a liquid is converted to a vapor -->As a liquid is turned to vapor, heat is lost and the remaining liquid is cooled Desflurane is significantly less potent than other volatile agents (need higher concentration to reach anesthetic levels) -Much more liquid desflurane is vaporized causing significant cooling of the liquid and vaporizer contianer -Desflurane vaporizers are actively heated to 39 C to combat this cooling

The driving force of the ventilator on the anesthesia workstation is accomplished with

The control mechanism of standard anesthesia ventilators uses compressed oxygen 100% to compress the ventilator bellows and electric power for the timing circuits. Some ventilators use a Venturi device, which mixes oxygen an air.

A patient has a blood glucose reading of 356 mg/dL. Which of the following is the correct hourly infusion rate for insulin to safely correct this hyperglycemia? Select one: a. 3.56 Units per hour b. 2.37 Units per hour c. 1.87 Units per hour d. 1.32 Units per hour e. 0.89 Units per hour

The correct infusion rate should be 2.37 units per hour. Plasma Glucose/150 = Hourly Insulin infusion rate 356/150= 2.37 U/hr The correct answer is: 2.37 Units per hour

Acoustic impedance during ultrasonography is the product of which of two characteristics?

The creation of an ultrasound image is determined by the reflection of the ultrasound waves occurring at interfaces between different mediums. The reflections occurring are dependent on the difference between the acoustic impedance between the two mediums (eg blood and tissue). Acoustic impedance is the product of the density of the medium and the propagation of sound through that medium. Normally, the propagation speed of sound varies slightly between mediums in the human body and therefore acoustic impedance is primarily dependent on density. Greater differences in density lead to "acoustic impedance mismatch" and prevent imaging in the far field (eg the density change from blood to air leads to impaired imaging of the lung). This is also the reason for the use of ultrasound gel on the transducer to reduce the large density change from the the transducer to the skin. Transducer aperture relates the diameter of the ultrasound beam and determines near field and far field length but does not determine acoustic impedance of medium Pulse duration is the time (usually measured in microseconds) a pulsed beam of ultrasound is released. Frequency is the number of cycles per unit time, or the reciprocal of the period (time between peaks and troughs). These are directly related to the acoustic impedance of biological material.

You are on a mission trip to a foreign country that only has vaporizers calibrated for use with halothane. However, you are only supplied with isoflurane. You have no choice but to fill the halothane vaporizer with isoflurane. What dial setting will be required to deliver 1 MAC of isoflurane in this scenario? Select one: a. 0.8% b. 1.2% c. 1.5% d. 2.2% e. 2.6%

The dial of a halothane vaporizer must be set to 1.2% to deliver 1 MAC of isoflurane. Halothane and isoflurane have similar vapor pressures, 244 mm Hg and 240 mm Hg, respectively. This means that the dial setting and the actual concentration of agent delivered will be very close. Therefore, to deliver 1 MAC of isoflurane or 1.2% sevoflurane, simply set the dial to 1.2%. Sevoflurane and enflurane also have similar vapor pressures. Filling a sevoflurane or enflurane vaporizer with the other will not cause too much of a change in agent concentration. A mnemonic for memorizing these relationships is as follows: HIGH SEA = Halothane and Isoflurane, which have similar vapor pressures, have HIGHER vapor pressures than Sevoflurane and Enflurane, which have similar vapor pressures. Remember that if you fill a vaporizer with an agent having a LOWER vapor pressure, then the delivered concentration will be LOWER than the dial setting. In contrast, if you fill a vaporizer with an agent having a HIGHER vapor pressure, then the delivered concentration will be HIGHER than the setting. The correct answer is: 1.2%

What is the difference between macroshock and microshock? Select one: a. Duration of shock b. Amperage of shock c. Voltage of shock d. Location of the shock e. Tissue damage caused by shock

The difference in macroshock and microshock is the location of the application of the electricity. Microshock is in or very near to the heart, wheras a macroshock is further away from the myocardium or applied external to the body. The correct answer is: Location of the shock

The reason a patient is not burned by the return of energy from the patient to the ESU is that

The exit current density is much less than...? Electrocautery units (ESUs) Operate by generating ultra high frequency (0.1-0.3 MHz) alternating electric currents and are commonly used today for cutting and coagulating tissue. Whenever a current passes through a resistance such as tissue, heat is generated and is inversely proportional to the surface area through which the current passes. At the point of entry to the body from the small active electrode or cautery tip, a fair amount of heat is generated. For the current to complete its circuit, the return electrode plate or dispersive pad (incorrectly but commonly called the ground pad) has a large surface area, where very little heat develops. The dispersive pad should be as close as is reasonable to the site of surgery. If the current from the ESU passes through an artificial cardiac pacemaker, the pacemaker may misinterpret the current as cardiac activity an dmay not pace, which is why a magnet placed over the pacemaker will turn off the pacemaker sensor, putting the pacemaker in asynchronous mode, and should be available.

Choose the correct statement regarding the oxygen fail-safe device to prevent hypoxic gas mixture delivery: Select one: a. Fail-safe device alarms when oxygen concentration falls below 21% b. Fail-safe device decreases or stops flow of all gases when pressure falls below 30 psi c. Fail-safe device will not allow a patient to be delivered hypoxic concentrations of nitrous oxide d. Fail-safe device only activates when central pipeline pressures fall below 45 psi e. Fail-safe device only activates when cylinder pressure falls below 40 psi

The fail-safe device decreases or stops flow of all gases when pressure falls below 30 psi. The fail-safe device is equipped on modern anesthesia machines to decrease the likelihood of hypoxic gas concentrations being administered to the patient. It activates when either oxygen pipeline or oxygen cylinder pressure falls below 30 psi, and acts to proportionally decrease or shut off completely the flow of all gases being administered. The valve does not prevent hypoxic mixtures of volatile agent or nitrous oxide being delivered if pipeline or cylinder pressures remain above 30 psi. One such occurrence is if the pipeline delivery system in the hospital system has the oxygen pipeline hooked up to the nitrous oxide source, the patient will be delivered 100% nitrous oxide even though you believe you are delivering 100% oxygen. The oxygen analyzer is used to monitor concentrations of oxygen, not the failsafe device. The correct answer is: Fail-safe device decreases or stops flow of all gases when pressure falls below 30 psi

What is meant by a fail-safe valve

The fail-safe valve device is designed to cut off the flow of all gases except O2 when the O2 pressure falls below a set value, usually about 25 psi

How does the fresh gas flow rate contribute to tidal volume?

The flow during the inspiration phase of the ventilatory cycle adds to the tidal volume. Let us assume that the respiratory rate is set at 10 bpm with an I:E ratio of 1:2 and a tidal volume of 1000 mL Each breath cycle is then 6 seconds long, 2 seconds for inspiration and 4 seconds for expiration. If the fresh gas flow is 6 L/min, 2x60= 6000 = 200 ml of fresh gas is added to each inspiration Most modern anesthesia ventilators automatically compensate for this addition to tidal volume

What is a hemiblock?

The left bundle bifurcates into two fascicles (anterior and posterior) and either one may be blocked. With a hemiblock the QRS duration is generally less than 120 msec unless there is an associated RBBB (commonly termed a bifascicular block)

What would be the cause when the bellows fails to rise completely between each breath?

The most obvious reason for this is that a leak exists in the breathing circuit, a disconnect has occurred, or the patient has become extubated. If the fresh gas flow is too low, it is possible for the patient to use O2 from the circuit faster than it is replenished

Which of the following statements is true regarding diffusion of gases in the lungs? Select one: a. Fick's Law of Diffusion states that diffusion of gases is inversely proportional to the difference in partial pressures of the gas b. The uptake of nitrous oxide from the lungs to the blood is about 3 L/min c. The much higher solubility of carbon dioxide allows it to diffuse across the alveolar membrane twenty times faster than oxygen d. The concentration effect refers to the alveolar atelectasis that occurs after long periods of oxygen administration at very high FiO2 e. None of these are true

The much higher solubility of carbon dioxide allows it to diffuse across the alveolar membrane twenty times faster than oxygen. Choice A is incorrect as Ficks Law states that diffusion is directly proportional to the difference in partial pressures of the gas.Choice B is incorrect as nitrous oxide diffused at a rate of 1 L/min.Choice D is incorrect as the concentration effect refers to increased uptake of anesthetic gas due to higher inspired gas concentration than the target blood level. Although it is true that administration of very high inspired concentrations of oxygen for long periods can cause atelectasis, it is referred to as absorption atelectasis not the concentration effect. The correct answer is: The much higher solubility of carbon dioxide allows it to diffuse across the alveolar membrane twenty times faster than oxygen

A negative pressure leak test

The negative pressure leak test is a universal test for leaks in the low-pressure circuit of anesthesia machines, regardless of whether the low-pressure circuit contains a check valve. Performing the test requires applying negative pressure with a suction bulb to the common gas outlet (from which the carbon dioxide absorber has been disconnected) with the machine's master switch turned off. With the suction bulb collapsed, each vaporizer is individually turned on and reinflation of the suction bulb indicates an internal leak in that vaporizer

A patient as the following vitals and lab values: Blood pressure 135/82, heart rate 78, respiratory rate 14, oxygen saturation 97%, FiO2 1.0, hemoglobin 15.2, PaO2 323 mmHg. What is the oxygen content of this patient? Select one: a. 15.2 mL/dL b. 20.9 mL/dL c. 22.5 mL/dL d. 26.2 mL/dL e. 29.1 mL/dL

The oxygen content is 20.9 mL/dL. CaO2 = (1.31 x Hb x SaO2) + (PaO2 x 0.003) CaO2= (1.31 x 15.2 x 0.97) + (323 x 0.003)= 20.879 = 20.9 Oxygen content on average is 19-21 mL/dL The correct answer is: 20.9 mL/dL

What is the oxygen content of a patient that has a hematocrit of 48, oxygen saturation of 100% and breathing an FiO2 of 65%? Select one: a. 17.2 mL/dL b. 19.4 mL/dL c. 21.9 mL/dL d. 23.1 mL/dL e. 15.8 mL/dL

The oxygen content is 21.9 mL of oxygen per dL. CaO2 = (1.31 x Hb x SaO2) + (PaO2 x 0.003) PaO2 can be estimated by FiO2 x 5 PaO2 = 65 x 5 = 325 CaCO2 = (1.31 x 16 x 1.0) + (325 x 0.003) = 21.935 = 21.9 The correct answer is: 21.9 mL/dL

As you attempt to mask ventilate a patient with an epic beard, you note the loss of significant amounts of gas due to leaking around the mask. In order to keep the reservoir bag full, you depress the oxygen flush valve. The oxygen flush valve provides what flow of oxygen (in liters per minute) directly to the common gas outlet? Select one: a. 15 - 35 b. 15 - 25 c. 35 - 75 d. 55 - 85 e. 75 - 90

The oxygen flush valve delivers oxygen at a pressure of 50 psig at 35-75 L/min The oxygen flush valve allows bypassing of the flowmeters and vaporizers, and provides oxygen directly to the common gas outlet. It is delivered at a pressure of 50 psig at 35-75 L/min and can lead to barotrauma if activated when a patient is connected to the system. Additionally, use of the oxygen flush valve bypasses vaporizers and will cause anesthetic gas concentrations to decrease. The correct answer is: 35 - 75

You are attempting to pass a Swan-Ganz catheter into the pulmonary artery in a patient with LBBB. When the hemodynamic tracing suggests that the catheter tip is in the right ventricle, the patient suddenly becomes bradycardic, with a heart rate of 25. What happened?

The patient is probably in complete heart block as a result of a catheter-induced RBBB (together with a preexisting LBBB). Fortunately the injury to the right bundle branch is often brief but temporary pacing may be required For patients with LBBB, consider the value of a PA catheter carefully before proceeding. In addition you should have emergency pacing equipment readily available to respond properly if this complication develops.

The addition of what device decreases the dead space in a circle system? Select one: a. Y connector b. Heat and moisture exchanger c. Carbon dioxide absorber d. APL valve e. Unidirectional valves

The presence of unidirectional valves decreases the amount of dead space to just the area past the unidirectional valves. One of the great disadvantages of a circle system is the addition of dead space caused by the size of the circuit. The presence of unidirectional valves decreases the amount of dead space to just the area past the unidirectional valves. This includes the Y piece and endotracheal tube. Fresh gas and scrubbed CO2 gas is available just on the other side of the inspiratory valve, and expired gases are prevented from being drawn back into the breathing system by closure of the exhalatory valve. The correct answer is: Unidirectional valves

Addition of what device decreases the dead space in a circle system?

The presence of unidirectional valves decreases the amount of dead space to the area just past the unidirectional valves One of the greatest disadvantages of the circle system is the addition of dead space caused by the size of the circuit. The presence of unidirectional valves decreases the amount of dead space to just the area past the unidirectional valves. This includes the Y piece and ETT. Fresh gas and scrubbed CO2 gas is available just on the other side of the inspiratory valve, and expired gases are prevented form being drawn back into the breathing system by closure of the expiratory valve

At about what volume will the pressure of a N2O cylinder start to fall?

The pressure gauge on a size E cylinder of N2O shows 750 psi when it is full and will continue to register 750 psi until about 3/4ths of the N2O has left the cylinder (liquid N2O has all been vaporized) A full cylinder of N2O contains 1590 L Therefore when ~400 L of gas remain in the cylinder, the pressure within the cylinder will start to fall

During anesthesia for a prone hemorrhoidectomy, an alarm for low pipeline pressure sounds. You switch the patient to manual bag ventilating and turn on the oxygen cylinder delivery line. The pressure regulator on the oxygen cylinder reduces cylinder pressure to what level before it enters the anesthesia machine flow valve? Select one: a. 30-32 psig b. 34-36 psig c. 40-42 psig d. 45-47 psig e. 50-52 psig

The pressure regulator reduces air pressure to 45-47 psig. Compressed gas cylinders are under high pressure and do not deliver a safe, constant pressure of gas as they are put into use. The high pressure regulator, located after the yoke check valve, seeks to reduce pressure of the cylinder to between 45-47 psig. This is below the typical pipeline pressure of 50 psig, which ensures that pipeline pressure will be preferentially selected for gas flow unless pipeline failure occurs and pressure falls below 45 psig. There is also a high pressure relief valve to reduce pressure in the event of regulator failure. The correct answer is: 45-47 psig

What physical principles are involved in the process of vaporization?

The saturated vapor pressure of the volatile anesthetic, which varies with temperature, determines the concentration of vapor molecules above the liquid anesthetic. The heat of vaporization is the energy required to release molecules of liquid into the gaseous phase. The liquid phase draws external heat during vaporization, or it will become cooler as molecules leave and enter the gaseous phase. To address this problem, vaporizers are constructed of metals with high thermal conductivity. High thermal conductivity ensures that there is a conduit of heat so the heat required for vaporization is constantly restored from the environment and the rate of vaporization of the volatile anesthetic is independent of changes in the temperature of the vaporizer

The phenomenon exploited during pediatric mask inductions with the simultaneous administration of nitrous oxide and high concentrations of volatile anesthetic is called Select one: a. Diffusion hypoxia b. Concentration effect c. Second gas effect d. Fick principle e. Bernoulli principle

The second gas effect is the phenomenon that is exploited during pediatric mask inductions. Nitrous oxide diffuses much more rapidly into the blood from the lungs than volatile anesthetic agents. This quick diffusion results in a decreased alveolar concentration of nitrous oxide in the lungs and increased concentrations of the remaining gases. Concentrating the remaining gases including the volatile agent speeds induction. Use of nitrous oxide also causes an increase in alveolar ventilation. Alveolar ventilation is inherently driven by gas diffusion across the alveolar membrane. As oxygen is dissolved into the blood, more air is pulled into alveoli to replace the deficit. Nitrous oxide diffuses into the blood very quickly (1 L/min) thus causing a large deficit and increasing flow of new gas into the alveoli.The second gas effect speeds both induction and emergence by this mechanism. Choice A is incorrect as diffusion hypoxia refers to the dilution of oxygen by the rapid diffusion of nitrous oxide out of the blood during emergence. Choice B is only partly correct as the concentration effect refers to the increased uptake of a single gas by using higher concentrations than target blood levels. The second gas effect can be considered a special case of the concentration effect. Thus, choice C is the better answer. Choice D is incorrect as the Fick principle (not to be confused with Ficks Law of Diffusion) is applied to the calculation of oxygen consumption. Choice E is incorrect as the Bernoulli principle deals with the relationship between fluid flow velocity and pressure. The correct answer is: Second gas effect

What is distal pulse amplification?

The shape of the arterial pressure wave changes as it travels from the low-resistance ascending aorta to the high-resistance arteriolar bed. This dramatic change in resistance causes the pressure wave to be reflected back toward the ascending aorta, influencing the shape of the pressure wave. Although the changes in shape do vary with age, sympathetic tone, and vascular impedance, generally peripherally measured arterial waveforms seem amplified an demonstrate higher systolic pressures, wider pulse pressures, and somewhat lower diastolic pressures. The mean arterial pressure is only slightly reduced

What does the c wave represent on CVP waveform?

This wave is caused by slight elevation of the tricuspid valve into the right atrium during early ventricular contraction. It correlates with the end of the QRS on EKG

Your 78 kg, 35 year old female patient having surgery for appendicitis is maintained on 2.1% sevoflurane for the duration of the case. What is the splitting ratio of gas flow through the vaporizing chamber to the flow through the bypass chamber of the vaporizer? Select one: a. 1:5 b. 1:9 c. 1:10 d. 2:5 e. 2:7

The splitting ratio would be 1:9 for a sevoflurane vaporizer set to 2.1%. Variable bypass vaporizers are used to administer sevoflurane, isoflurane, halothane, and enflurane. Variable bypass means the fresh gas flow through the vaporizer is split into two streams: one that flows through the vaporizing chamber and one that flows through the bypass chamber. The two streams are reunited at the vaporizer outlet where the fresh gas flow continues through the breathing circuit to the patient. The vaporizing chamber contains liquid volatile agent as well as agent vapor. The vapor is at a concentration determine by its saturated vapor pressure (which is the partial pressure of the vapor when it is at equilibrium between liquid and vapor states). Saturated vapor pressures for sevoflurane, isoflurane, halothane, and enflurane are 160, 240, 243, and 170 mm Hg, respectively. This means that a vaporizing chamber filled with sevoflurane will have a vapor pressure of 160 mm Hg or a concentration of 21% (concentration = saturated vapor pressure/atmospheric pressure X 100% = 160 mm Hg/760 mm Hg X 100% = 21%). That is much higher than the concentration needed for anesthesia (about 2%). No matter what flow of gas passes through the vaporizing chamber, the concentration of the gas leaving the vaporizing chamber will be 21% sevoflurane. This gas stream must be diluted to safe anesthetic levels by the fresh gas flow passing through the bypass chamber. The ratio of gas flow through the vaporizing chamber to the gas flow through the bypass chamber is referred to as a splitting ratio. The concentration dial adjusts the splitting ratio. For sevoflurane, in order to get a final concentration of say 2.1%, one-tenth (2.1%/21% = 1/10) of the total fresh gas flow must go through the vaporizing chamber. So if the total fresh gas flow is set to 1 L/min and the dial setting is at 2.1%, 100 mL/min of FGF will flow through the vaporizing chamber and the remaining 900 mL/min will flow through the bypass chamber. A useful equation for calculating splitting ratios: Flow through vaporizing chamber = Total FGF X [(Dial setting/100)/(Sat VP/Atm P)] For the scenario presented in this question, choose any FGF rate: Flow through vaporizing chamber = 1 L/min X [(2.1/100)/(160 mm Hg/760 mm Hg)] Flow through vaporizing chamber = 1 L/min X 0.1 = 0.1 L/min = 100 mL/min This means that for every 1 L of gas, 100 mL will be diverted in the vaporizing chamber and 900 mL will go through the bypass chamber. Thus the ratio is 100 mL:900 mL or 1:9. The correct answer is: 1:9

The diameter index safety system (DISS)

The system is based on matching specific bores and diameters that are assigned to the specific gases. The DISS should prevent attachment of gas administration equipment to the wrong gas. This is not the protective system for cylinder yoke attachments that use the pin index safety system. DISS connectors must be screwed on and are therefore not considered "quick-connectors" They are required on the machine end, and are optional on the wall end, of hoses connecting anesthesia machines to the wall. A gas specific "quick-connector" is an alternative for teh wall connection. DISS connectors are also sometimes found on the gas outlets of portable tanks

An oxygen E cylinder reads 650 psig. If the tank is open to allow 4 L/min of flow, how long will the tank be useable? Select one: a. 53 minutes b. 215 minutes c. 108 minutes d. 78 minutes e. 30 minutes

The tank can be used for 54 minutes at this rate. The formula for this uses the following information P1 for your tank pressure when it is full V1 is the tank volume when it is full P2 is the pressure that the tank is currently at V2 is the volume of oxygen or air you wish to determine is left for delivery to your patient P1/V1=P2/V2 P1= 2000 V1=660 L P2 =650 V2= X 2000/660=650/X X=214.5 L You then take how many liters of your oxygen or air in the tank and divide it by your flow rate, as you are using that many liters of gas per minute. 214.5 L x (min/4L)= 53.625 = 54 min Another explanation that may help: The tank is useable for 53 minutes at a flow of 4 L/min. Since pressure and volume in an oxygen gas cylinder are directly proportional, use this equation: P1/V1=P2/V2 Solving for V2 gives the equation: (V1/P1)X P2 = V2 (660 L/2000 psig) X 650 psig = 214.5 L Another strategy for finding the remaining volume, is to view the pressure reading as a fraction of full pressure and then multiply that by the full volume to get the fraction of the volume left over. Volume left = 650 psig/2000 psig X 660 L Volume left = 0.325 X 660 L Volume left = 214.5 L If the flow is set at 4 L/min, then the time left on the tank is 214.5 L/(4 L/min) or 53.6 minutes. Always round down in these problems. There are 53 minutes left on the tank. The correct answer is: 53 minutes

If a nitrous oxide E-cylinder is known to have released 600 liters from a full tank what would the PSI gauge approxmiately read? Select one: a. 600 psig b. 660 psig c. 745 psig d. 1900 psig e. 2200 psig

The tank pressure gage will read 745 psig. The pressure gauge on a nitrous oxide E-cylinder will read 745 PSI until there is only 400 L left in the tank (3/4 empty). Approximately 1,600 liters of nitrous oxide are held in a full E cylinder. 2000 psig is the service capacity of an oxygen E cylinder, which holds approximately 660 liters. The correct answer is: 745 psig

What is the frequency of the train of four stimulation? Select one: a. 1/10 Hz b. 1 Hz c. 2 Hz d. 5 Hz e. 10 Hz

The train-of-four frequency is two Hertz. One Hertz equals one cycle a second. Two Hertz is two cycles a second. As a train-of-four is delivered at two Hertz, a single train-of-four is delivered over 1.5 seconds. The twitches are delivered at 0 seconds, 0.5 seconds, 1 second, and 1.5 seconds. The correct answer is: 2 Hz

You have completed induction of a morbidly obese patient undergoing decompression of lumbar nerve roots. As you attempt to turn the desflurane vaporizer to deliver at 6%, you find you are unable to turn the dial as you currently are delivering sevoflurane. The purpose of the safety interlock on vaporizers is to: Select one: a. Prevent more than one vaporizer to be used at a time b. Allow gas flow into only the selected vaporizer c. Ensure proper attachment of vaporizer to anesthesia machine d. Prevent escape of volatile agent when vaporizer is turned off e. All of the above

The vaporizer interlock prevents you from engaging more than one agent at a time. The vaporizer interlock is primarily to prevent the use of more than one agent at a time, however it also ensures that the vaporizers are properly seated in their respective positions and that gas can only enter the selected vaporizer for mixing. It also prevents leakage of vaporizer out into the gas flows when the vaporizer has been turned off. The correct answer is: All of the above

The tubing that connects the APL valve to the waste gas scavenging system is the same diameter as the tubing or the connector that is connected to

The ventilator pressure relief valve The wast gas scavenging system is connected to the APL valve and the ventilator pressure relief valve with 19- or 30 mm tubing. The circle system connectors and the connection for the reservoir bag are 22 mm, while the common gas outlet and ETT connections are 15 mm. All of these measurements are internal diameter

When the oxygen flush valve is pressed, what must you be sure of on the ventilator?

The ventilator should not be in the inspiratory phase of positive pressure ventilation The oxygen flush valve can apply oxygen to the breathing system at the pressure of the pipeline supply (e.g. approximately 50 psi) possibly causing barotrauma. If the APL valve is open and the scavenging system is of the open type, barotrauma is minimized. If oxygen is being supplied by the gas cylinder mounted on the anesthesia machine, the cylinder pressure is decreased to approximately 45 psi in the anesthesia machine, and this pressure is applied to the breathing circuit when the oxygen flush valve is pressed. During the inspiratory phase of positive pressure ventilation, both the ventilator relief and pop-off valves are closed, and pressing the oxygen flush valve will apply high pressure to the breathing circuit. The oxygen flush valve is positioned distally to the rotameters and vaporizers in an anesthesia machine

What are common ports on the pulmonary artery catheter (5)?

Thermistor Pulmonary artery distal port Proximal infusion port Right atrial port Balloon inflation port

Basis of temperature monitoring in anesthesia

Thermistors (resistors with resistance inversely proportional to temperature) quantify temperature

What does the a wave represent on CVP waveform?

This wave is due to increased atrial pressure during right atrial contraction

What does the y descent represent on CVP waveform?

This wave is produced by the tricuspid valve opening in diastole with blood flowing to the right ventricle Occurs before the P wave on EKG

Color Flow Doppler

This doppler modality is an application of pulsed wave doppler technology that allows determination of velocity at a specific location. Velocity is color coded and superimposed over a 2D image. However, like pulsed wave doppler, color doppler is limited by signal aliasing. Fluid or tissue that moves toward the probe causes compression of sound waves and an increase in the received frequency, whereas motion away from the probe leads to reduced frequency. Although ultrasound machine color maps can often be adjusted, by convention flow toward the probe is colored red, where as flow away from the probe is coded blue BART: Blue Away Red Toward

What does the v wave represent on CVP waveform?

This wave arises from the pressure produced when the blood filling the right atrium comes up against the closed tricuspid valve. It occurs as the T wave is ending on EKG

What ECG finding suggest hypokalemia?

U waves (which occur after the T wave) are prominent and may merge with the Twave, creating a broad T wave and a prolonged AT interval. In addition, the P wave may be amplified and ST depression may occur

Closed-Circuit anesthesia

Use of FGFs exactly equal to the uptake of oxygen and anesthetic agents requires: 1) very low FGF 2) total rebreathing of exhaled gases after absorption of CO2 by CO2 absorbent 3) closed APL or ventilator relief valve Advantages: INC heat and humidification of gases, DEC pollution and agent use, DEC cost Disadvantages: DEC rate of agent concentration change; may cause hypoxic/hypercarbic mix; risk of excessive agent concentration

Describe the esophageal detector device

Uses a negative pressure bulb It is essentially a bulb that is first compressed and then attached to the ETT after the tube is inserted. The pressure generated is about -40 cm H2O. If the ETT is placed in the esophagus, the bulb will not inflate. If the ETT is in the trachea, then the air from the lung will enable to bulb to inflate (usually a few seconds but can take >30). A syringe that has a negative pressure applied to it has also been used. Although initial studies were very positive about the use of the EDD, more recent studies show that up to 30% of correctly placed ETT in adults may be removed because the EDD has suggested esophageal placement. Misleading results have been noted in patients with morbid obesity, late pregnancy, status asthmaticus, and copious ET secretion, wherein the trachea tends to collapse. Its use in children younger than 1 year of age has shown poor sensitivity and poor specificiety. Although CO is needed to get CO2 to the lungs for a CO2 gas analyzer to function, a CO is not needed for EDD.

What leads are most helpful when looking for a bundle branch block?

V1, V6, and to some extent II The QRS duration should be more than 120 msec to identify a bundle branch block. Not every wide QRS is a bundle branch block. The differential diagnosis also includes a ventricular beat, intraventricular conduction delay, hyperkalemia, drug effect, and WPW with conduction through an accessory pathway

A fiberoptic bronchoscope is useful for airway management of the patient with a difficult airway, and the suction channel of the scope may facilitate intubation by facilitating all of the following actions EXCEPT Administer oxygen Ventilate the patient during bronchoscopy Advance the scope over a wire inserted percutaneously through the larynx Spray local anesthetic Aspirate tracheal secretions

Ventilate the patient during bronchoscopy The suction port of a fiberoptic bronchoscope is designed primarily to aspirate secretions. However, it may also be used to administer oxygen to a spontaneously breathing patient or to spray local anesthetic in the airway or on the vocal cords. It may also be used to pass the scope over a retrograde wire. The patient cannot be ventilated via this port

An admixture of room air in the waste gas disposal system during an appendectomy in a paralyzed, mechanically ventilated patient under general volatile anesthesia can best be explained by which mechanism of entry?

Waste gas disposal systems, also called scavenging systems, are designed to decrease pollution in the OR by anesthetic gases. Passive-waste gases flow form the anesthesia machine to a ventilation system on their own Active- anesthesia machine is connected to a vacuum system Positive-pressure relief valves open if there is an obstruction between the anesthesia machine and the disposal system, which would then leak gas into the OR. A leak in the soda lime canister would also vent to the OR. Given that most ventilator bellows are powered by oxygen, a leak in the bellows will not add air to the evacuation system. The negative-pressure relief valve is used in active systems and will entrap room air if the pressure in the system is less than -0.5 cm H2O

Pulse pressure variation

When a patient is receiving positive pressure ventilation measurement of pulse pressure variation or systolic pressure variation can be done. When positive pressure is applied to the lungs during mechanical ventilation (during inspiration), venous return to the right side of the heart is reduced, decreasing cardiac output and systolic BP. Pulse pressure is the difference between systolic and diastolic BPs. PPV is defined as the pulse pressure between two breaths (PPmax) minus the pulse pressure during positive pressure ventilation (PPmin) divided by the mean pulse pressure (PPmax+PPmin/2) times 100% For example, if the PPmax is 90 (systolic BP 160-diastolic 70) and the PPmin is 70 (systolic BP 130, diastolic 60) then the PPV = (90-70)/80 = 25% Patients are considered fluid responsive (ie an increase in BP or CO) if the PPV is >15% and not fluid responsive if the PPV <7% Alternatively, SPV, which is the difference in systolic BP during inspiration (positive intrathoracic pressure) and expiration, can be determined with normal values of 7-10 mm Hg. Hypovolemic patients have an elevation in SPV. Patients with an SPV >10 mm Hg are fluid responsive, whereas those with an SPV of <5 mm Hg are not fluid responsive For both SPV and PPV the patient must be mechanically ventilated and in a regular rhythm (not in atrial fib) for the calculations. Measurements of BP are with an arterial line.

Air cylinder

Yellow E cylinder: 2000 psi, 650 L H cylinder: 6000-9000 L

How can you check the competency of a circle system?

You should close the pop-off valve, occlude the Y-piece, and press the O2 flush valve until the pressure is 30 cm H2O The pressure will not decline if there are no leaks Then you should open the pop-off valve to ensure that it is in working order. In addition, you should check the function of the unidirectional valves by breathing down each limb individually, making sure that you cannot inhale from the expirator limb or exhale down the inspiratory limb

CaO2 (in mL/L blood)

[13.4 x Hb conc (in mg/dL) x SaO2/100] + [0.0031 x PaO2 mm Hg)

CvO2 (in mL/L blood)

[13.4 x Hb conc (in mg/dL) x SvO2/100] + [0.0031 x PvO2 mm Hg)

Aspiration ETCO2 analysis

able to detect inspired CO2 to detect rebreathing

Airway pressure

airway resistance + alveolar pressure (chest and lung compliance)

What color is a nitrogen tank

black

The major component, by weight, in currently used carbon dioxide absorbents is

calcium hydroxide While some absorbents have low percentages of sodium hydroxide or potassium hydroxide, most of the absorbent consists of calcium hydroxide Barium hydroxide is no longer used

Motor evoked potentials

must avoid muscle relaxants

The fail-safe valve on an anesthesia machine is

open if oxygen pressure is present The fail-safe valves on anesthesia machines are on if oxygen pressure is present. It is important to understand that this valve is strictly pressure related. As long as there is oxygen pressure on the machine, the valves will be on, permitting flow of other gases such as nitrous oxide, carbon dioxide, air, helium, nitrogen, etc. It is therefore possible to still deliver a hypoxic mixture to the patient even with a functioning fail-safe valve. In contrast, newer machines have proportioning systems that ensure a minimum concentration of oxygen is delivered at the common gas outlet

Plateau pressure

pressure during inspiratory pause (static compliance)

Arteries used for arterial BP cannulation

radial: superficial with collateral flow (Allen's test) Ulnar: deeper than radial Brachial: large and easily identified, less wave form distortion, easily kinked Femoral: increased infection risk, prone to pseudoaneurysm Dorsalis pedis and posterior tibial: distorted wave form, use modified allen's test Axillary: risk of nerve damage, air thrombi can access cerebral circulation

Variable bypass vaporizers

total gas flow is split into carrier and bypass gas flows Carrier gas: flows over liquid agent in vaporizing chamber & saturates with agent "carries" agent to vaporizer outlet Bypass gass: exits vaporizer unchanged Two flows mix at the vaporizer outlet and exit machine at common fresh gas outlet Does not risk overdose if FGF decreases Temperature compensation with metallic strip that adjusts flow Agent specific vaporizers Automatic compensation for elevation

Open-drop

volatile anesthetic dripped onto gauze mask on pts face