The Anesthesia Machine2
Define ventilator frequency.
# of respiratory cycles per minute.
What are some advantages of the semiclosed and closed circle systems?
(1) conservation of airway moisture & body heat. (2) decreasing pollution of the surrounding atmosphere with anesthesic gases when the fresh gas inflow is set at less than the patient's minute ventilation.
What are some advantages of the semiclosed and closed circle systems?
(1) conservation of airway moisture & body heat. (2) decreasing pollution of the surrounding atmosphere with anesthesic gases when the fresh gas inflow is set at less than the patient's minute ventilation.
What is the PISS position for N?
1, 4
What is the PISS position for Air?
1, 5.
What are some components of an anesthesia workstation?
1. Anesthesia machine (mmHg regulating & gas mixing components) 2. Vaporizers 3. Breathing circuit 4. Ventilator 5. Scavenging system 6. Respiratory and physiologic monitoring systems (ECG, A-Line, Temp, SaO2, and inhaled/exhaled concentration of O2, CO2, anesthetic gases, & vapors)
What are some hazards associated with cylinders?
1. Incorrect valve: it may be labeled for the gas contained but have a valve for another gas. 2. Incorrect color: they may colored in a different color than there standard color. 3. Damaged valve: may cause the cylinder to have a leak 4. Asphyxia: a sudden discharge of large quantities of gas other than oxygen from a cylinder into a closed space could displace the air from that space, creating a dangerous condition. It produces an oxygen deficient concentration. 5. Fires: Occurs if an oxidizing gas is present. Oxygen & N2O are both oxidizing gases. They are flammable. 6. Explosion: A cylinder that is incorrectly filled may not have the proper pressure relief device 7. Projectile damage: If a cylinder falls and the valve breaks, b/c it is under pressure, the rapid escape of the gases may cause it to shoot like a rocket 8. Contaminated cylinder contents: may contain potentially dangerous amounts of other compounds it is not supposed to contain 9. Nitrous oxide: people use it for substance abuse 10. Thermal injury: frost bite from people who use it recreationally 11. Blocked flow meters: this is if the flow meter is integrated, no oxygen will flow
Describe the 5 immediate functions/activations that occurs when the anesthesia machine is connect the O2 source (cylinder or pipeline).
1. Power outlet accessory: provides pressure to vent. 2. Activation of the O2 flush valve. 3. Activation of the pressure sensor shut-off valve. 4. Activation of the failure alarm system. 5. Activation of 2nd stage pressure regulator.
How often should the air in the operating room be exchanged?
15 times/hours
When an NO2 E cylinder is full, what is the capacity & pressure?
1590L at 745 psi.
What is the PISS position for O2?
2, 5
What is the PISS position for NO2?
3, 5
How much NO2 is left in the tank when the pressure gauge changes?
400L. The pressure gauge will change once all the liquid NO2 is depleted. When it changes there is only 1/4 left in the cylinder.
How are oxygen, nitrous oxide, and air gases that are used in anesthesia typically delivered to the anesthesia machine? At what pressure must these gases be delivered for proper function of the anesthesia machine?
Gases used in anesthesia are delivered to the anesthesia machine as compressed gases using cylinders attach to the machine or through the hospital's central supply source. These gases must be delivered at 50 psi for the anesthesia machine to work properly.
What does soda lime consist of?
H2O, calcium hydroxide, & a small amount of Na & K hydroxide that function as activators
What does Amsorb Plus consist of?
H2O, calcium hydroxide, & calcium chloride.
Describe the Y-piece connector in the circle system circuit.
Has a curved elbow. An outer diameter of 22mm to fit a face mask. An inner diameter of 15mm to fit an ETT connector.
What are three types of humidifiers used for anesthesia and in the intensive care unit?
Heat & moisture exchange. Heated H20 vaporization & humidifiers. Nebs.
Describe the pressure gauges on the anesthesia machine.
High pressure gauges (a Bourdon type gauge), which measures the pressure within a given cylinder. There is usually one for the cylinder & one for the pipeline.
Describe anesthetic breathing system humidification. What effect does chemical neutralization of carbon dioxide have on this process?
Humidification is a form of vaporization in which H20 vapor (moisture) is added to gases delivered by the anesthesia breathing system to minimize H2O and heat loss. The chemical neutralization of carbon dioxide forms heat and H2O which can be used to humidify and heat the gases.
Define inspiratory & expiratory phase time.
I:E ratio is the ratio of inspiratory phase time to expiratory phase time
Contrast the relationship between content and pressure in O2 vs NO2.
In a container containing a nonliquefied gas like our O2 cylinder. The pressure declines steadily as the contents are withdrawn. The pressure can be used to measure the cylinder contents. The pressure in an oxygen cylinder is directly proportional to the volume of oxygen in the cylinder. In a container containing a liquefied gas like in our nitrous oxide container the amount of gas remaining cannot be determined by looking at the pressure. The pressure depends on the vapor pressure of the liquid and is not an indication of the amount of gas remaining in the cylinder as long as the contents are in the liquid phase. In a nitrous oxide container the pressure remains constant until all the liquid has evaporated. When all of the liquid has evaporated, the pressure will decline. The only way to determine the amount of liquid in these cylinders is by weighing the actual cylinder. At the point where the liquid is gone in a N2O cylinder and the pressure gauge drops the container is more than ¾ empty. So approximately 400L remains when the pressure begins to decrease.
How is this the CO2 absorbent sizing system defined?
In anesthesia practice, the granule size is between 4 (four quarter inch openings per linear inch) and 8 mesh (eight eight-inch openings per linear inch). 4 mesh is bigger than 8 mesh
What is the purpose of the fail-safe (shut off) valve? What triggers the fail-safe valve on the anesthesia machine?
In the event of O2 supply failure, the fail safe valve is designed to prevent hypoxic gas mixtures by shutting off or proportionally decreases the flow of all gases. Trigger is when the pressure in the oxygen delivery line fails below 20-25 psi.
What are the two limbs in the cycle system & in which direction do they flow?
Inspiratory limb: leaves machine & goes to patient. Expiratory limb: leaves patient & goes to machine.
What is the heat of vaporization?
Is the number of calories requires at a specific temperature to convert 1g of a liquid into a vapor.
What effect does tracheal intubation or the use of a laryngeal mask airway have on airway humidification? What are the negative consequences of this?
It bypasses the upper respiratory tract, so, the burden of warming and humidifying the gas to the lower respiratory tract. Negative consequences: Dries up mucosa Impaired cilia function. Impaired surfactant function. Inspissation of secretions. Atelectasis. Rise in aveolar-arterial gradient.
Describe the parts of a hanger yolk.
It contains a body retaining screw, nipple, PISS, washer, & a check valve to prevent backflow of gas into cylinder.
Why are contemporary vaporizers unsuitable for use with desflurane?
It could lead to anesthetic overdose. Vapor mmHg of desflurane is 3-4x that of other violative anesthetics. It has a vapor mmHg of 1atm at 20C. The vaporizer is electrically heated to 23C-25C and pressurized with a backpressure regulator to 1500 mmHg.
How does channeling in the canister affect the efficiency of carbon dioxide neutralization?
It decreases efficiency because the bulk of the granules are bypassed.
Does Amsorb Plus degrade inhaled anesthetics?
It doesn't.
What is the impact of the rebreathing of anesthetic gases in a semiclosed circle system?
It influences the inhaled anesthetic concentration: During induction, the uptake of the anesthetic gas is very high. Rebreathing of exhaled gases depleted of anesthetic gases dilutes the concentration of anesthetic in the fresh gas inflow. Increasing the delivered concentration of anesthetics offsets this. Dilution of anesthetic lessens as uptake diminishes.
Whats is a cylinder hanger yolk?
It is the attachment on the anesthesia machine where the cylinders are set into place.
Describe operating room scavenging.
It is the collection and removal of vented gases form the OR If bag/vent switch is set to bag, the gas come the the APL valve, but, if it is set to vent, the gas come from the vent relief valve. The amount of delivered gases use to anesthetize the patient usually exceeds the patient's needs. If the bag/vent switch is set to vent, some anesthetic breathing systems will direct the drive gas inside the bellow canister to the scavenging system. If sidestream gas analyzer are use, the analyzed gas exiting the analyzer must be directed to the scavenging system if not returned to the breathing system.
Why is calibration of the oxygen monitor so important?
It is the only machine safety device that detects problems downstream form the flowmeter.
What is the purpose of unidirectional valves in the circle system? What would occur if one of the unidirectional valves should become incompetent?.
Keep the gases moving one way, permit positive pressure breathing, & prevents rebreathing of gases until it has passed through the CO2 absorbent. If the valves are stuck open rebreathing and hypercapina can occur. If the valves are stuck closed breath stacking and barotrauma can occur
What is advantageous about the corrugated tubing in the circle system?
Large bore provides minimal resistant. Corrugated tubing provides flexibility, resist kinking, and promotes turbulent flow (instead of laminar flow).
Where might be the source of a low-pressure leak of nitrous oxide?
Leak inside the anesthesia machine. Leak between the machine and patient.
Are inspired concentrations of oxygen more or less predictable when nitrous oxide is also being delivered in a closed circle anesthetic breathing system? Why?
Less predictable, decreased uptake of NO2 with time in the presence of unchanged uptake of O2 can result in a decreased concentration of O2 at the alveoli.
Describe the O2 flush valve.
Located at machine outlet to circuit. When pressured it flushed the system with 35-75L/min. Used to reestablish pressure. NEVER USE WHEN ATTACHED TO PATIENT. MAY CAUSE BAROTRAUMA.
What are factors that increase the amount of compound A?
Low fresh gas flows (<1L/min). Higher concentration of sevoflurane. Higher absorbent temperature. Absorbent desiccation (drying) Use of baralyme rather than soda lime. Length of time under anesthesia.
What is a disadvantage to the closed circle anesthetic breathing system?
Low fresh gas inflow which prevents rapidly changing the delivered concentration of anesthetic gases and oxygen.
What does 3AL marking on a cylinder indicate?
Made of aluminum & can be used in MRI.
What does 3AA marking on a cylinder indicate?
Made of steel.
What is the TEC 6 vaporizer?
Made specifically for Desflurane Vapor pressure of Des is 3-4 x's that of other inhaled anesthetics
Are vaporizers interchangeable?
Modern vaporizers are agent specific Precisely calibrated to compensate to changes in temperature and variations of gas flow Constructed of metals with high thermal conductivity, allowing heat to flow from the vaporizer into the anesthetic in the liquid phase, supplying the energy for the heat of vaporization
How do spirometers work?
Most commonly, a rotating vane is present in the expiratory limb (Wright respirometer); the flow of gas across the vanes causes them to rotate and the number of rotations/time is measured
Describe the mechanics of a conventional anesthesia machine ventilator during inspiration.
Most conventional anesthesia vents are pneumatically driven by O2 or air that is pressurized. During inspiration the O2 for air is routed to the space inside the ventilator casing between the compressible bellow & the rigid casing. Pressurized air or O2 entering this space forces the bellows to empty its contents into the patient's lung through the inspiratory limb of the circuit. The pressurized air or O2 also forces the ventilator relief valve to close preventing inspiratory anesthetic gas from entering the scavenging system.
Describe the Medical Gas Pipeline System.
Most hospital supplied gases enter the operating room from a central source through pipelines to color coded wall outlets. Central source may be located outdoors or indoors.
In the operating room, what are the Occupational Safety and Health Administration (OSHA) recommendations for the maximum concentrations of nitrous oxide and volatile anesthetics in parts per million?
NO2 = 25ppm Volatile anesthetics = 2ppm NO2 c voliatile anesthetics = 0.5ppm
Are flowmeters for various gases interchangeable?
No, each flowmeter is calibrated for it's particular gas and very few gases have the same density and viscosity.
Does a manual positive-pressure leak test check the integrity of the unidirectional valves?
No, the breathing system will pass the test even if there unidirectional valves are incompetent of stuck shut.
Describe the vaporizer flow pattern in relation to variable-bypass and flow-over refer to.
O2 (O2 + N2O) enter vaporizer and pass through a filter Variable bypass means slipping the FGF coming into the vaporizer into two parts: 1. 20% or less of the FGF goes into the vaporizing chamber where is become saturated (flow-over) with the vapor of the liquid anesthetic. 2. The rest of the FGF bypasses the vaporizing chamber through the bypass chamber. Both parts mix together at the patient outlet side of the anesthesia machine. Flow-over refers to the process where the FGF flowing into the vaporizing chamber becomes saturated with anesthetic vapor molecules. A relief valve exists which will open if gas flow exceeds that which is required for delivery of gas concentration on the dial
What are the US gas colors?
O2 = green NO2 = blue Air = yellow CO2 = grey N = black
Describe O2 supply storage.
O2 is stored as a liquid (cheaper to store large supplies this way) Stored is a place where potential ignition is low. Stored below it's boiling point (100C) Stored in G or H cylinders. Usually stored at ground level for easy filling.
What are the potential hazards of scavenging systems? •
Obstruction of the scavenging pathway; this can lead to excessive positive pressure & barotramua. Excessive vacuum which can lead to excessive negative pressures.
What is common gas outlet (fresh gas outlet)?
Only one outlet on the anesthesia machine, compared to multiple gas inlets. Must have an anti-disconnect device to prevent accidental disconnection from the breathing circuit Oxygen from the flush valve goes directly from the intermediate pressure system to this outlet, directly to the patient
Describe the mechanically driven piston type of ventilators found on some newer anesthesia machines.
Operates like a plunger on a syringe to deliver the desired tidal volume or airway pressure to the patient.
Contrast passive & active scavenging.
Passive: The waste gases exiting the anesthesia machine enters into a passive pipeline, which carries the gases out of the area This type of system usually employs a closed scavenging interface since the waste gases are exiting at a passive rate; basically they are exiting the system as quickly as they are added to the system If an open scavenging interface is used, the WAGs may preferentially exit via the open interface vents, rather than via the pipeline (follow the path of least resistance) Active: Takes the WAGs from the breathing circuit and transfers them to the hospital's vacuum system This requires an open scavenging interface to decrease the likelihood of creating negative pressure in the breathing circuit, or allowing pressures to increase to dangerous levels May use closed interfaces with valves (better)
What anesthetic techniques can lead to operating room pollution?
Poor fitting face mask. Flushing the anesthetic delivery circuit. Filling the anesthetic vaporizers. The use of uncuffed endotracheal tube. Failure to turn off the NO2 flow or vaporizers at the end of the anesthesia. The use of semiopen breathing circuits like Jackson-Rees.
Why is the TEC 6 pressurized?
Pressurizes to ~ 2 atm Controls amount of desflurane output
Describe nebulizer humidifiers used for anesthesia and in the intensive care unit.
Produce a mist of microdroplets of H2O suspended in a gaseous medium & can be used to deliver meds.
Describe the O2 flush valve.
Provides oxygen at 35 - 75 L/min directly to the common gas outlet, bypassing flowmeters and vaporizers When actuated, the oxygen may reach a patient (if connected to the system) at a pressure of 45 - 55 psi Potential barotrauma, particularly a pediatric or infant Used to rapidly refill or flush the breathing circuit Must have a built-in rim to prevent inadvertent activation and spring to prevent prolonged activation
What factors contributes to the degradation of inhaled anesthetics by soda lime?
Retrograde flow & desiccation.
Describe the Diameter Index Safety System.
Safety system used in the pipeline system to prevent improper connection of supply hoses. Does not prevent hypoxic gas mixture from being delivered to the patient. The connection points are gas specific and are noninterchangeable (located on the wall or ceiling). DISS connector consist of a body, nipple, and nut combination. The face plates are marked with the specific gas for that pipe. It usually has an identifying color. It is usually a quick connection The two prominences on the hose connector mate with the two slots on the wall outlet
What is required to control pollution of the atmosphere with anesthetic gases?
Scavenging of waste anesthetic gases. Periodic preventive maintenance of anesthesia equipment. Attention to anesthetic technique. Adequate ventilation of the OR.
What is the most commonly used circle breathing system used in the United States?
Semiclosed which is associated with rebreathing.
What size cylinder is most commonly used in anesthesia?
Size E
What are two types of chemicals that are used to neutralize carbon dioxide? What products are formed? Are the neutralization reactions endothermic or exothermic?
Soda lime & Amsord Plus H2O, carbonates, and heat. Exothermic
Contrast the color change of soda lime granules with those of Amsorb Plus.
Soda lime contains a ethyl violet indicator dye which changes the color from white to purple. Exhausted granules may change back to their white color, but will not regain their absorbent ability. Amsorb plus contains an indicator dye that changes granule color from white to purple. Exhausted granules do not change back to white.
Describe the intermediate pressure system.
Starts at the 1st stage pressure regulator. Ends at 2nd stage regulator. Includes all part that receives gases at low & constant pressure (30-55 psi). It includes: Pipeline inlet & pressure gauges. Vent power outlet accessory. O2 flush valve. Supply failure alarm system. 2nd pressure regulator Flowmeter valves.
Describe the low pressure system.
Starts at the second stage regulator, ends at the common gas outlet. The pressure is reduced to 15-30 psi, allowing the safe delivery of gas to patients. Includes: Flowmeters Vaporizers Temp compensating bypass valve.
What does the term temperature-compensated refer to? Between what temperatures is vaporizer output reliably constant?
Temp-compensated refers to the fact that, as the vaporize temperature changes temp compensating bypass valve influences the proportioning of total gas flow between the vaporizing and bypass chambers. For example, if the temp drops in the vap chamber, the temperature sensing device will increase gas flow into this chamber to offset the effect of decreased anesthetic liquid vapor. Also, vap chambers are usually made out metals with high thermal conductivity to further minimize heat loss. Vaporizer output temp is constantly between 20C & 35C.
What are the current recommendations for preanesthesia checkout procedures? How do these apply to newer machines with automated checkout procedures?
The current recommendation for pre-anesthesia checkout were developed in 2008. They provide a guideline that can be use with anesthesia delivery systems. For newer machines, some items might not be check by the automated system and must be manually check.
Describe the mechanics of a conventional anesthesia machine ventilator during exhalation.
The driving gas is either vented in the room or through a scavenging system and the bellow refills as the patient exhales.
What is the optimal carbon dioxide absorbent granule size?
The granule size is design as a mesh size which refers to the number of openings per linear inch in a sieve through which the granules particles can pass.
Why do the carbon dioxide absorbent granules change color?
The have pH sensitive dye that changes color when the granules are exhausted.
Define carbon dioxide absorbent absorptive capacity. What can cause a decrease in absorptive capacity?
The max amount of CO2 that can be absorbed by 100g of CO2 absorbent.
What is the most frequent cause of channeling in the carbon dioxide absorbent granule-containing canister? How can it be minimized?
The most frequent cause of channeling is loose packing of absorbent granules. Gently shaking the canister before use ensures firm packing. The canister is designed facilities uniform distribution.
What two features do scavenging systems have to minimize their potential hazards?
The positive pressure relief valve opens when the pressure reaches 10cm H2O and allows gas to escape into the room. The negative pressure relief valve opens if the pressure is too negative and allows room air or be drawn in.
What parts of a circle system are eliminated in anesthesia machine ventilators when the "bag/vent" selector switch is set to "vent"?
The reservoir bag & APL valve.
What two factors influence the efficiency of carbon dioxide neutralization?
The size of the granules & the presence or absence of channeling.
How does the size of the carbon dioxide absorbent granules affect the efficiency of carbon dioxide neutralization?
The smaller the granules, the better absorptive efficiency because of increase surface area, but the smaller granules increase resistance by creating smaller interstices that the gas must pass though. The optimal granule size is a compromise between absorptive efficiency & resistance to airflow through the canister.
Describe the degradation of inhaled anesthetics by soda lime to compound A.
The strong bases in Soda Lime degrades sevoflurane & halothane to compound A.
Factors that can increase CO produce from CO2 absorbers.
The type of inhaled anesthetic used (desflurane > enflurane > isoflurane) Higher concentration of inhaled anesthetics. Higher absorbent temperatures. Dry absorbent.
How is the potential risk of filling the agent-specific vaporizer with the erroneous volatile anesthetic minimized?
The use of an anesthetic-specific key filler device.
Why should the O2 be disconnected at the end of the day?
There is a constant flow of 50-150ml/min even when flowmeter is turned off.
What are the risks of heated water vaporizers and humidifiers?
Thermal injury Nosocomial Infections Increased work of breathing. Increased risk of malfunction because of complexity.
What is a spirometer?
They are used to measure the patient's exhaled tidal volume.
How are inhaled gases normally humidified in awake patients breathing through their native airway?
Through the upper respiratory tract especially the nose.
Why is silica added to soda lime?
To hardness & minimize alkaline dust formation which can cause bronchospasm if inhaled.
hy are calcium sulfate and polyvinylpyrrolidine added to Amsorb Plus?
To increase hardness.
Describe a closed anesthetic breathing system. What is the inflow volume of fresh gases in a closed anesthetic breathing system?
Total rebreathing of exhaled gases after absorption of CO2 and the APL valve of the ventilator is closed. Inflow volumes of fresh gases = 150-500mL/min which will satisfy patient's metabolic requirement (150-250mL/min during anesthesia) and replace anesthetic gases lost by tissue uptake.
What safety features are present on the flowmeter knobs.
Touch (texture) and color-coded to prevent use of the wrong gas. Oxygen knob is fluted, versus "gnarled," larger than the others, and protrudes further out. Oxygen located furthest to the right.
What are the dangers of the closed circle anesthetic breathing system?
Unpredictable and possibly insufficient concentration of oxygen. Unknown and possibly excessive concentrations of potent anesthetic gases.
Describe the O2 proportioning device.
Used to ensure that nitrous oxide can only be delivered in the presence of oxygen Prevents delivery of low oxygen content nitrous oxide to the patient When nitrous oxide is used, oxygen is entrained (added) to create a minimum FiO2 of 21 - 25%
How can the potential problem of the inadequate delivery of oxygen using a closed circle anesthetic breathing system be minimized?
Using a O2 analyzer on the inspiratory or expiratory limb of the closed circuit system.
What is vapor pressure? What influence does temperature have on vapor pressure?
Vapor mmHg is the pressure that is create by the collision of vapor molecules with each other and the container in which they are stored. A decrease in temp, decreases the number of molecules in the vapor phase (drops vaporization) which decreases the vapor mmHg
Why do volatile anesthetics require placement in a vaporizer for their inhaled delivery to patients via the anesthesia machine?
Vaporizer allows the volatile anesthetic to change from a liquid to a gas (that can be delivered to the patient through the breathing circuit) that can be delivered with accuracy and predictability.
What are the most important preoperative checks?
Verification that an auxiliary O2 cylinder and self-inflating manual ventilation device (Ambu-bag) are available and functioning. A leak test of the machine's low pressure system. Calibration of the O2 monitor. A positive-pressure leak check of the breathing system.
Define tidal volume.
Volume of gas entering and leaving patient during inspiration & expiration.
When should the CO2 canister be replaced?
When 50-70% of the absorber granules have turned purple.
What factors increase retrograde flow & desiccation through the CO2 absorber?
With conventional breathing system design: removing the breathing bag fresh gas flow rate of 5L/min or higher without a patient attached opening the APL valve occluding the Y-piece
What is a high pressure regulator?
Works to control the high pressure within the cylinder. Reduces the high pressure to 45psi.
Can a hypoxic mixture be delivered from the anesthesia machine with an intact fail-safe valve? Explain.
Yes, the fail-safe valve only shuts off if there is a drop in pressure. Theoretically, is oxygen flow is zero, but gas mmHg is maintained the valve will remain open.
How often are cylinder tested?
every 5 years. * = every 10 years
Explain hlh
hlh -- Higher vapor pressure (VP) agent in a lower VP vaporizer chamber higher concentration delivered
When would a H cylinder be used?
in rural areas or areas without a pipeline.
Define expiratory pause time.
interval from the end of expiratory flow to the start of inspiratory flow
Describe the size classification of cylinders.
A (smallest)-H (largest)
What are the advantages of active scavenging with a waste gas receiver mounted on the side of the anesthesia machine?
A needle valve that allows the clinician to manually adjust the amount of vacuum flow through the scavenging system. A needle valve that can be adjusted such that the 3L reservoir bag will be slightly inflated and appear to "breathe" with the patient. A waste gas receiver doesn't require a strong vacuum to operate.
At what pressure do gases usually enter the anesthesia machine from the pipeline system?
A pressure regulator usually pipes gases in at 50-55 psi.
How is the delivery of two different volatile anesthetics to the same patient via the same anesthesia machine prevented?
A safety interlock mechanism ensures that only one volatile anesthetic is used at one time.
Describe the pressure relief devices.
A safety mechanism that prevent explosion of the cylinder. Rupture disc: when a predetermine pressure is reached the disc ruptures & allows the contents to be released. This will protect against excess pressures that can result for overfilling or high temp. Fusible plug: Thermally operated. Protects against excessive pressure caused by hight temps. When the set pressure is exceeded, the pressure in the cylinder forces the spring to the left, and gas flows around the safety valve seat to the discharge channel. Pressure relief valve: This spring loaded device is designed to reclose and prevent cylinder contents from being discharged after a normal pressure has been restored. Disc/plug combo: sensitive to changes in both temp & pressure.
Describe the two types of scavenging systems used in the operating room.
Active: Is connected to the hospital's vacuum system and gases are drawn from the machine by a vacuum. Passive: Is connected to the hospital's ventilation duct and waste gases flow out of the machine on their own.
What are the advantages & disadvantages of HME humidifiers over other types of humidifiers?
Advantages: Simple & easy to use Lightweight Not dependent on external power source Disposable, Low cost. Disadvantages: Not as effective as heated H2O vaporizers or humidifiers in maintain patient's temp Add resistance & increase the work of breathing, so, they should be used with caution in spontaneously breathing patients Can become clogged with patient's secretion or blood., Can increase dead space. This can cause significant rebreathing in pediatric patients (low-volume HMEs can be used).
What is the supply failure alarm system?
Alarm sounds when O2 pressure drops, but before activation shut-off valve. (below 28 psi.)
What is the purpose of flowmeters on an anesthesia machine?
Allows for the control and measurement of gas flow.
What is the function of the ventilator's pressure relief valve?
Allows gas to escape if pressure reach 65-80cm H20
Describe the function of the APL valve when the "bag/vent" selector switch is set to "bag."
Allows venting of excess gas from breathing system into the waste gas scavenging system. Allows assisted and controlled ventilation to the patient by manual compression of the gas reservoir bag. The valve should be fully opened during spontaneous ventilation so that circuit pressure remains negligible throughout inspiration and expiration. Must be partially closed during manual or assisted bag ventilation. If it is open too wide, too much volume is allowed to escape. If it is closed too tight, not enough volume escapes creating higher pressures & larger volumes.
Describe NO2 supply storage.
Also stored as a liquid . Regulators may become so cold that they freeze (open slowly). There should be warning signs where these tanks are stored b/c if there is a leak in an enclosed room, a hypoxic mixture may be produced.
What are two different ways in which anesthesia machine ventilators are powered?
Are powered by compressed gas, electricity, or both.
Explain lhl
lh" -- Lower VP agent in higher VP vaporizer chamber lower concentration delivered
How do flowmeters on an anesthesia machine work?
mmHg from the gas flow raises the bobbin. The upper end or the equator of the bobbin indicates the ml/min or L/min flow rate.
What information should be present on the cylinder's label?
name of gas, hazards, warnings, name & address of manufacture & distributor.
Why are standing or ascending bellows preferred over hanging or descending bellows?
Ascending are preferred because if there is a leak in the breathing system or if the system becomes disconnected the bellow won't rise, but, in a descending bellow, the bellow will continue to rise and fall even if there is a leak or disconnection.
Contrast the difference between ascending and descending bellow?
Ascending bellows compress downward during inspiration & ascend upward during expiration. They provide 2-4 cm of PEEP. Descending bellow compress upward during inspiration & drop down during expiration.
When should an O2 sensor be used?
At all time when the anesthesia machine is in use.
Why is oxygen preferred over air as the ventilator driving gas?
Because if there is a leak in the bellow the FiO2 will increase
Where is the dead space in the circle system?
Between the y-piece and the patient.
Describe the different cylinder parts.
Body: made of steel or aluminum Valve: attached to the neck of the cylinder, used for filling & discharging gas, made of bronze or brass, regulates pressure down. Port: point of gas exist, usually covered until cylinder is opened. Stem: located within the valve, closes and open the valve.
To what temp is the TEC 6 heated & why?
Boils at approx. 22.8 degrees C Electrically heated to approx. 39 degrees C If not heated, the large amounts of desflurane required (d/t MAC value 4 - 9 x's other VA's) would cause excessive cooling of the vaporizer making conventional temperature compensating mechanism ineffective
What are some disadvantages of the circle anesthetic breathing system?
Bulkiness & loss of portability. Increased resistance because of unidirectional valves & CO2 absorbent. Opportunity for malfunction because of machine's complexity.
How is carbon dioxide eliminated in a semiclosed or closed anesthetic breathing system?
By chemical neutralization.
How is carbon dioxide eliminated in open and semiopen breathing systems?
By venting all exhaled gases to the atmosphere
How do you calculate how much O2 you have left in a cylinder?
Capacity in L/Service Pressure = Contents Remaining (L)/Gauge Pressure.
When should the O2 tank be changed?
Change when PSI fall below 1000.
What does channeling in the carbon dioxide absorbent granule-containing canister refer to?
Channeling is the preferential passage of exhaled gas through the CO2 absorber canister via pathways of low resistance.
What can cause a decrease in CO2 absorbent absorptive capacity?
Channeling of exhaled gas can decrease absorptive capacity.
What are the classifications of a circle system and on what does this depend?
Classification of a circle system is semiopen, semiclosed, or closed depending on the fresh gas flow.
How is the delivery of erroneous gases to the anesthesia machine minimized?
Color coding, PISS, DISS
What are the components of the circle system?
Common gas inlet (fresh gas inflow): where gas from the common gas outlet enters. Inspiratory valve: unidirectional valves Y-piece: connects to the airway being used. Expiratory valve: unidirectional valves APL valve (pop off valve): pressure relief valve Bag/vent switch: allows the user to either manually ventilate or use the mechanical vent. Reservoir bag: provides mean for manual ventilation. Available in 1L, 2L, or 3L CO2 absorbent Corrugated tubes O2 sensor: determines the concentration of O2 moving towards the patient.
What is the advantage of heated water vaporizers and humidifiers over HME humidifiers?
Compared to HME, they can delivered higher humidity
How often should these checkout procedures be performed?
Complete anesthesia machine and circle system function checkout should be done daily before the first case. An abbreviated checkout should be performed before each subsequent use
Which O2 sensor do not need to be calibrated?
paramagentic
Define inspiratory pause time.
period from the end of inspiratory flow to the start of expiratory flow.
Define inspiratory phase time.
period of time between the start of inspiratory flow & the beginning of expiratory flow the sum of the inspiratory & the inspiratory pause time.
Which O2 sensors need to be calibrated?
polarographic (Clark Electrode) & galvanic (fuel cell)
Define resistance.
pressure difference per unit flow across the airway; it usually increases as flow increases
Define compliance.
ratio of a change in volume to a change in pressure
Define minute volume.
sum of tidal volumes in one minute.
Define inspiratory flow time.
the period between the beginning and end of inspiratory flow
Define expiratory flow time.
time between the beginning and end of expiratory flow
Define expiratory phase time.
time between the start of expiratory flow and the start of inspiratory flow or it is the sum of the expiratory flow time and the expiratory pause time
Define expiratory flow rate.
volume of gas per unit time returned from the patient during the expiratory phase
Define inspiratory flow rate.
volume of gas per unit time that passes from the patient connection of the breathing system to the patient
How does tipping of a vaporizer affect vaporizer output?
•Tipping can cause liquid anesthetic to leak into the bypass chamber which would result in increased vapor concentration.
What does a leak check of the machine's low-pressure system evaluate? Why is this so important?
Confirms the integrity of the anesthesia machine from the flowmeters to the common gas outlet. It evaluates the portion of the anesthesia machine that is downstream from all safety devices, except the O2 monitor. This part is the most vulnerable part of the anesthesia machine because the components located within this area are the ones most subject to breakage & leaks. Leaks can lead to hypoxia or patient's awareness.
Describe the Pin Index Safety System (PISS).
Consist of holes on the cylinder valve positioned in an arc. Pins on the yolk or pressure regulator are positioned to fit into these holes. The holes and pins must be aligned in order for it to seat. Prevents the connect of wrong cylinders.
What is a bourdon gauge?
Consists of a closed coiled tube connected to the cylinder in which pressure is to be sensed. As the pressure increases the tube will uncoil, while a reduced pressure will allow the tube to coil more tightly. This motion is transferred through a link to a gear connected to an indicating needle.
Describe the High Pressure System.
Consists of those parts that receive gas at cylinder pressure (~45 to 2000 psi); this includes cylinder gas down regulated by a first stage regulator. Starts at cylinders. Ends at 1st stage regulators. System includes: Hanger yoke Hanger yoke check valve Cylinder pressure regulator Cylinder pressure gauge
What is the purpose of the cylinders of oxygen and nitrous oxide that are found on the back of the anesthesia machine?
Cylinders provide a backup sources of gases in the event that the central supply fails.
What information is included on the cylinder markings?
DOT number, materials used in manufacturing, service pressure, serial #, ID of purchaser & manufacture, initial & re-test date
Why is the oxygen flowmeter the last flowmeter in a series on the anesthesia machine with respect to the direction in which the gas flows?
Decrease the possibility that an leak in the first two meters will reduce O2 concentration.
What does the 2nd stage pressure regulator do?
Decreases gas pressure to 16 psi (gases coming out of pipeline is between 40-50 psi). After passing this regulator is sits in stand b at the flow control valve.
Describe the degradation of inhaled anesthetics by soda lime to carbon monoxide.
Desiccated soda lime can degrade sevoflurane, isoflurane, enflurane, & desflurane to CO.
What causes the development of fire and extreme heat in the breathing system? How can this be avoided? •
Desiccation of the CO2 absorbent Baralyme (no longer clinically available) can lead to fire within the circle system with sevoflurane use due to poorly characterized chemical reaction that produces sufficient heat & combustible degradation products. Avoid using desiccated CO2 absorbants.
Describe heat and moisture exchanger (HME) humidifiers. What is the difference between an HME and an HMEF?
Devices that are placed between the y-site of the circle system and the patient's ETT which conserves some the exhaled H2O & heat & returns it to the inspired gases. HMEF can also filter out bacteria & viruses.
What is disadvantageous about the corrugated tubing in the circle system
During positive-pressure ventilation, some of the gas distends the corrugated tubing and some is compressed in the circuit which lead to a smaller delivered tidal volume.
What are some advantages to the closed circle anesthetic breathing system?
Economy of use. Max humidification and warming of inhaled gases. Less pollution of the surrounding atmosphere with anesthetic gases
How does the circle anesthetic breathing system get its name?
Essential components are arranged in a circular manner.
Why does atmospheric water vapor accumulate as frost on the outside surface of oxygen tanks and nitrous oxide tanks in use?
Expansion of gas (O2) and the vaporization of a liquid gas (NO2) absorb heat from the tank and surrounding atmosphere. Internal icing doesn't occurs because compressed gases are free of H2) vapor.
How does the circle system prevent rebreathing of carbon dioxide?
Expired air is filter through a CO2 absorbent which neutralize CO2.
What if the carbon dioxide absorbent canister fails to become warm during use?
Failure of the canister to become warm suggest that CO2 neutralization make not be taking place.
Where might be the source of a high-pressure leak of nitrous oxide? .
Faulty yokes attaching the NO2 tank to the anesthesia machine. Faulty connection from the central NO2 gas supply to the anesthesia machine
When an Air E cylinder is full, what is the capacity & pressure?
625L at 1900 psi.
When an O2 E cylinder is full, what is the capacity & pressure?
660L at 1900 psi.
Why is the water in the soda lime carbon dioxide absorbent canister hazardous?
The H2O from the neutralization of CO2, H2O present in soda lime granules, & H2O condensed from the patient's exhaled gas leach the alkaline bases from the soda lime granules and make a slurry containing NaOH & KOH in bottom of the canister which cane be corrosive to the skin.
Why is the water formed by the neutralization of carbon dioxide useful?
The H2O is useful in humidifying gases and for dissipating heat generated in these exothermic reactions.
What are the advantages of the reservoir bag on the circle system?
The bag serves as a safety device, because its distensibility limits pressures in the breathing circuit to < 60 cm H2O even when the valve is closed. The gas reservoir bag maintains an available reserve volume of gas to satisfy the patient's spontaneous inspiratory flow rate (up to 60L/min) which exceeds conventional gas flows (3-5L/min) from the anesthesia machine.
In a closed circle anesthetic breathing system, to what extent is the inhaled concentration of anesthetic dependent on the exhaled concentration of anesthetic? What is the potential problem with this? How can this problem be partially offset?
The concentration of the exhaled gases reflects tissue uptake of anesthetics. The composition of the inhaled gas is influenced by the composition of the exhaled gas. Initially, tissue uptake is maximal and rebreathing of this gas dilutes the inhaled concentration of the anesthetic delivered to the patient. High inflow concentration are needed to offset this maximal uptake by tissues, but once uptake has decreased only small amounts of anesthetic need to be added to inflow. • The potential problem is that it becomes difficult to estimate the inhaled concentration delivered to the patient through a closed anesthetic system. This can be offset by administering higher fresh gas inflow (3L/min) for about 15mins before instituting the use of a closed anesthetic breathing system.
