Module 8

what do we do differently when a laser is being used?

not a ton. preop and premeds are the same. careful with sedation and narcs if airway obstruction is possible. ETT types - red rubber (flammable), silicone w tape (but toxic ash if it burns), PVC (but toxic gases released if it burns), or laser resistant ETT (can still burn, it's just harder)

what is the "fire triangle?"

oxygen, fuel, and an ignition source these are the things required for combustion

50 mA

pain

when is red and infrared used

pulse ox, CO2 monitors

how to protect against electrocution?

regular inspection and maintenance of equipment can also put something non conductive around pacer wires...a glove, syringe

the 1993 National Electric Code (NEC) requires either...

requires either ground fault circuit interrupters (GFCI) or isolated power systems only in wet locations, not necessarily all anesthetizing locations

resistance equation

resistance (ohms) = potential (volts) / current (amps)

what is impedence?

resistance to flow. impedance is provided by dry, intact skin. therefore, EKG and other electrodes (and grounding plates) must be moistened with conductive gel. Because of the impedance of the skin, if sufficient current does pass through it, heat is generated causing burns at the point of contact.

6000 mA

respiratory paralysis

what is monochromatic

same wavelength!

newer model pacemakers are...

shielded.

GFCIs and unprotected power systems do what when faults occur?

shut off power. we don't like this, because we need our equipment to monitor our patient.

when is UV light used clinically

some gas analyzers

what is grounded equipment

the third wire which protects people from exposure to short circuits

what can happen with internal pacemakers?

their electrodes can interpret external energy sources as QRS complexes, thus inhibiting the firing of the pacemaker. if there are no or few spontaneous beats of the heart and the pacemaker is inhibited, cardiac output may fall precipitously. In the past, or with older model pacemakers, external energy sources such as electric motors, microwave ovens, antitheft devices in libraries or stores, diathermy, some monitors, and peripheral nerve stimulates caused problems.

most critical preventative measure?

GROUNDING all objects in the room maintained at a common electrical potential = earth elaborate precautions were taken to equalize the potential of all objects within the OR

what is grounding?

Grounding reduces potential differences to zero; no current can flow. A basic safety measure which should be utilized in areas of danger (devices connected to a patient; or in areas where high currents exist, or where electricity and water coexist like the kitchen or bathroom). Two meanings, often confused- both circuits and electrical equipment are grounded

moral of the story?

all suspect equipment must be removed from service pending exam by qualified personnel to avoid risk of patient injury or death

what is collimated

all waves are parallel. the light stays parallel instead of expanding out like a flashlight light. increases concentration of the laser light

what color glasses are needed for Argon laser

amber

A =

amps

what is required for electrocution in the OR?

an ungrounded piece of equipment with a leakage current, grounded subject, and low resistance pathway to the heart. even a fraction of the current passing through the body may cause v fib if it transits the myocardium. much less current is required to stop the heart (microamperes) if it is conducted within the body than is required to cause burns when current is applied to the body surface. even potential differences as small as one volt may cause current to flow to the heart thru a CVP or Swan, or through an esophageal stethoscope or external pacemaker wires. a circuit may be completed by the anesthetist touching inadequately grounded equipment and the patient or IV simultaneously.

impedance is lower if skin is ___________

damp/wet

impedance is higher if skin is ______

dry

what do you fill the ETT cuff with during laser airway surgery?

methylene blue and saline b/c it's easier to see if the cuff breaks and the fluid has a higher heat capacity and will resist burning

microA=

microamps

microshock is measured in

microamps, microA

mA=

milliamps

impedance is lowest if...

needles or cannulae pierce the skin

are you completely safe if you have grounded equipment?

no! if you are in contact with a live wire and the ground, you complete a circuit in which electrons can travel from the electric company, to your site, and back through your body to the electric company.

what is a grounded circuit

a way of returning spent electrons to the earth

5 mA will cause

maximum safe amount

10-20 mA

"let go" threshold before muscle contraction

what do you do if ETT catches on fire?

1. stop ventilation and disconnect O2 source (disconnect the insp limb, it's faster) 2. extubate (remove combustibles from airway, douse with water, save the tube for later analysis) 3. reestablish ventilation --> mask ventilate until you are sure the fire is out. reintubate with a SMALLER DIAMETER tube 4. diagnose injury via laryngoscope or bronchoscope, begin therapy based on findings 5. monitor 24 hours in ICU probably --> short term steroids, antibiotics, vent support as needed

electrical safety rules

1. All equipment should be grounded 2. Use (and understand!) isolated power systems and line isolation monitors 3. Ensure routine preventive maintenance is being done on all devices 4. Be safe with cords (remove from service if damaged, don't run wheels over them, grasp plug not cord to remove from receptacles, tape them to the floor if they're in a pathway, avoid cheater plugs, multiple outlet plugs, and extension cords (they leak current), avoid excessively long power cables, knots, crushing or stress in power cables). 5. Read and follow safety and operating manuals 6. Remove dropped or damaged equipment from service 7. Don't allow ECG wires to touch potentially grounded conductors (floor, metal table parts, ether screen or tube tree) 8. Don't touch intracardiac leads of any kind unless wearing gloves- especially not while touching a metal surface or piece of equipment. 9. Use the correct patient cable (ECG leads have been plugged into AC outlets! Patients have been burned by pulse oximeter probes used with incompatible monitors (even by the same manufacturer) 10. Beware pools of IV fluid in proximity to electrical apparatus 11. Don't place liquids on electrical equipment 12. Be vigilant for failure of other electrical devices (monitors, vent, pacemakers) whenever electrosurgery units (ESU) are in use 13. External pacemakers (should wrap wires with rubber gloves, use a non-electric bed, avoid or check for sources which might cause external interference with the pacemaker's function i.e. radio-frequency interference from the Bovie). 14. Internal pacemakers (usually avoid the unipolar cautery on these cases, use bipolar, check EKG after each ESU activation, check pacemaker after surgery to ensure it's working properly, assume patient with PM is 100% dependent until proven otherwise, consider having external PM available).

what are OR hazards?

1. EKG electrodes may provide a path to ground 2. diathermy (if poor or no grounding plate, burns are possible at any place where patient skin contacts grounded metal)

what are the three special characteristics of laser light?

1. coherent 2. collimated 3. monochromatic these properties allow the laser to focus a large amount of energy to cut/coagulate

laser hazards

1. damage to eye and skin 2. electric shock 3. fire 4. explosion (contact with gas tubing, ETT, drapes, sponges) 5. noxious fumes (mutagenic, infectious, pulmonary irritant)

what are hazards of diathermy?

1. decreased area of contact at grounding plate will produce a burn at that site 2. detached grounding plate will cause current to go to ground at any convenient place (i.e., through EKG electrodes, through a metal ring on the patient's finger if it's in contact with metal on the grounded OR table, etc. this is why patient's aren't allowed to keep rings on) 3. the hot knife causes radio-frequency interference with patient monitors like the EKG, pulse ox, etc (pulse ox has less chance of electrical interference)

key points of a line isolation monitor (LIM)

1. isolated power systems are used to lessen the possibility of electrical injury to OR personnel and the patient (macroshock), while avoiding loss of fxn of electrical apparatus in the case of a short. If you used a regular circuit breaker or GFCI system, short circuits would result in loss of electric power to everything on the same circuit. we don't want to lose monitors and lighting in the OR! when a LIM rings (threshold: 2-5 mA), there is short circuit in an electrical device --> unplug them starting with the last one plugged in. if you don't have a flashlight, use your laryngoscope

protective measures for laser

1. laser safety committee (safety program, policies, inservice, QA) 2. containment of beam (regular equipment maintenance, warning signs, instruments with low specular reflectance) 3. eye protection 4. protect patient tissue near laser site with wet sponges, evacuate fumes with sxn, fire protection 5. use specialized ETT for laser airway surgery (laser resistant ETT)

what is a conductor?

A conductor is usually metal; outer electrons are loosely bound and can readily move through the metal in response to an electrical potential difference. Examples: human body, copper wire.

what is a transistor?

A device for controlling and/or amplifying an electron current, involving passage through a semiconductor, without vacuum, and at low power consumption

what is a fuse?

A device which is designed to fuse (melt) before vital components of electrical apparatus are damaged by an inappropriately high current flow. Melting of the fuse interrupts current and prevents potential damage.

what is a resistor?

A device which opposes current flow

what is an isolated power system?

A system of power used in operating rooms that has no direct connections to power supplied to the hospital, and is isolated from ground. The isolation transformer supplies the "motivation" for current to flow in the secondary electrical system

what is a capacitor?

AKA condensor A device which stores a charge

what is electricity?

AKA electromotive force. defined as an electrical potential difference (two sites with differing electron content) which causes a current of electrons to flow from higher to lower concentrations of electrons

what is induction shielding?

As current flows, magnetic fields are always set up which can cause "induction" of current flow in nearby objects. A byproduct of current which may pose danger to people or simply interference in the operation of other devices. Devices may be "shielded" to prevent this.

what is the electromagnetic spectrum?

Electromagnetic energy can be classified by wavelength into a spectrum of which visible light (400-700 nm) is only an octave.

what is an insulator?

In an insulator, the electrons are firmly bound and not able to move in response to an electrical potential difference.

what is a Line Isolation Monitor (LIM)?

Monitors integrity of isolated power system and alarms when current flows to ground. Usually set to alarm at 2-5 mA current leakage to ground (depending on age of system). Notice that the V-fib microshock threshold is much less than this. Leaks above threshold will trigger an alarm, but monitors and other devices will still work. This is unlike a household circuit breaker (or a GFCI) which interrupt power in the presence of short circuits.

who makes safety regulations r/t OR fires and explosions?

National Electric Code (NEC) and National Fire Protection Association (NFPA) these are industry groups that issue advisory standards. they aren't laws, but are mandatory for hospital accreditation b/c their standards have been adopted by the joint commission. also mandatory for hospital licensure.

what is the unit for resistance?

Ohms.

what is the most flammable ETT?

PVC probably can wrap it with aluminum or copper-foil tape

what is a semi-conductor?

Possesses conductivity intermediate between insulators and conductors, usually strongly dependent on temperature. Electronic devices are harmed by excesses of temperature. The semiconductor has replaced the vacuum tube and the transistor as the basis of modern electronic apparatus on the basis of its small size and mass, ability to be mass produced, reliability, and cost.

what provides the maximum inhibition of static sparks?

RELATIVE HUMIDITY!! should be kept around 50-60% in OR this is why all OR's have humidity gauges

characteristics of isolated power systems

Ungrounded (main hospital supply is a grounded system). Secondary transformer (also called isolation transformer). Power is supplied by hospital main electrical supply to the primary transformer. The power is transferred to the isolated loop, but is without connections to ground (as white or neutral wires are throughout normal household or hospital circuits). so, you SHOULD be able to touch a live wire in the OR while you are grounded and suffer no ill effects. but don't try it

what is a current flow?

When a potential difference exists between an object of high electron content and one of low electron content, and the two objects are connected by a conductor, a circuit is formed and current flows. Heat and sometimes light may be produced as a byproduct if the conductor resists the passage of the current i.e. toaster wires.

what happens if a live wire is touched?

a current flows through a person's body if there is a pathway to earth through the body.

oil in valves of compressed gas apparatus can lead to...?

adiabetic explosions

what do all glasses have to have?

all must have side protectors

what is coherent

all photons go up and down at the same time, which increases laser energy

prevention of diathermy injury?

anesthesia shares the responsibility of ensuring that the grounding plate is placed correctly (close to operative site, not placed so that the heart is between the knife and the plate) also ensure that there is no other potential path to ground (like EKG electrode) b/w the knife and the plate check grounding plate contact initially and when patient is repositioned no contact of patient with grounded apparatus keep Bovie cables away from pacemaker leads observe fire precautions and limit O2, N2O, and flammable prep agents (ex: isopropyl alcohol), esp in head and neck surgery check dispersive electrode contact when pt is repositioned

what is protective that we can wear in the OR?

anti-static shoes. they have enough resistance so that large current cannot pass, but they do allow small static electricity to dissipate

when are radio waves used

apnea monitors

what is "helium protocol?"

because helium has a high thermal diffusivity and doesn't support combustion, it can be used at a Fihelium of 0.6 and FiO2 < 0.4.

when are radar waves used

beepers

what are some ignition sources?

before scavenging, oxygen and fuel was abundant in the form of stray vapors of volatile and flammable anesthetic gases the most common ignition source causing OR explosions was STATIC ELECTRICITY

what do transducers do?

change kinetic energy into electrical energy

Household wiring characteristics

circuits are grounded. Ordinarily, the neutral (white) wire and the third (green or bare, equipment grounding) wire are connected to ground (earth). Current is carried to electrical devices via the black wire. The spent electrons return through the white wire, to the circuit breaker service panel. From there, they flow through a grounding rod through the earth, to the electric power company.

what color glasses needed for CO2 laser

clear

what is an explosion?

combustion in which the rate of heat production far outstrips the rate of heat removal

what kind of waves are light and sound?

complexes of sine waves. any complex wave such as BP tracing, or the sounds heard when auscultating the heart, can be resolved by Fourier analysis into its component sine waves

what is "current density"

current flow/unit area. The greater the current density, the greater the heating effect.

what does a third wire do?

electrical appliances with a third wire are grounded. If a third (grounding) wire is present, the lowest resistance pathway for the current is through the third wire, and you are safer. Equipment that lacks a third (grounding) wire poses a risk!

what is diathermy?

electrocautery, hot knife, Bovie (brand name) resistance to the flow of electricity causes electron "friction" which generates heat. This heat is used to cut or coagulate tissue. A current of high frequency is made to pass through an electrode, through a patient, and out through the grounding plate. Tissues are burned to cut or coagulate them by high current density at the Bovie end; no burn occurs where the current leaves the body, even though the same amount of current is present at the grounding plate, since the current leaving the body is spread over a much greater area. Thus the proper name is "dispersive electrode" rather than grounding plate.

Pacemaker risks

external pacemakers have wires leading from the unit directly to the myocardium thus presenting risk of microshock.

what is the electrical resistance formula similar to?

fluid resistance. resistance = pressure/flow for fluids

what color glasses are needed for NdYAG laser

green

what two things is it important to distinguish between in relation to grounding?

grounding can be used in 2 senses 1. grounding circuits 2. grounded equipment

what does combustion produce?

heat, light, CO2, and water

what is the purpose of the isolated power system?

lessen the possibility of macroshock. short circuits ("first faults") convert the supplied electrical power circuit to a grounded system (electrical current in contact with the case of a piece of equipment flows down the third wire, then goes into the ground. this creates a potential difference of 120 volts b/w ground and the current in the secondary. If a "second fault" occurs (a second piece of equipment is shorted out), a person who is grounded (touching a piece of plumbing or a grounded piece of equipment) is at risk.

what causes increased electrical resistance?

longer or thinner wire, there will be increased resistance to electrical flow. this is the basis for a strain gauge transducer.

macroshock is measured in

mA (milliamps)

what are isolated power systems designed to protect against?

macroshock they do not protect against microshock

10 microA

maximum 60 hz leakage current

why wet sponges?

they absorb more heat

1 mA will cause

tingling sensation

what would a person feel when a current passes through the body?

tingling, pain, and then muscle contraction. may finally get ventricular ectopy and v fib if the current is s trong enough. incidence of v fib is higher if pre-existing disease

is diathermy unipolar or bipolar?

unipolar

what type of cautery is more risky?

unipolar

what is bipolar diathermy?

used for smaller, more sensitive areas. bipolar is a different type that prevents widespread tissue coagulation. the part held by the surgeon is like a forceps, current enters one prong and leaves the other, so no grounding plate is required. useful for neurosurgery where there is no convenient spot for a grounding plate and greater precision is necessary.

100 microA

v fib

100-300 mA

v fib, resp tract fxn still intact

how is electrical power supplied?

via a live wire and a neutral wire (which is grounded at the supplier) devices are also grounded at the site where they are used

is the OR wet or dry environment?

wet

list types of wavelength from shortest to longest

x-rays ultraviolet light purple blue green yellow orange red infrared-radio-radar-television

does N2O support combustion?

yep, don't use it