4b. Anesthesia Equipment

Question 1

What are the two functionaly systems of safe delivery of inhalant anesthetics?

Answer 1

1. life support - oxygen and everything associated w/ breathing and assisted ventilation
2. Inhalant drug delivery - getting a safe amount of gas into patient to keep them under

Question 2

What are the basic continuous machine design

Answer 2

High pressure system: high pressure supply of gases by cylinders or pipelines, pressure gauges (regulators) to control flow of gases into the machine
Flow meters: intermediate pressure system
Low pressure system: vaporizer to create accurate mix of gases at known concentration, breathing circuit - to deliver to patient

Question 3

What is the high pressure system?

Answer 3

o2 and n2o source
can be pressurized cylinder or pipeline supply
pipeline oxygen supply: 50psi, tans located elsewhere in building, chainted to wall
Cylinders: O2 supplied around 2000psi (needs to be reduced to about 45psi when entering anesthetic machine

Question 4

What are the gas tank color doding system?

Answer 4

oxygen tank colors: white, green, white + green
N2o - blue

Question 5

What are the most common size for O tanks?

Answer 5

Etanks

Question 6

What is the hanger yoke assembly?

Answer 6

connects cylinder to machine; ensures unidirectional gas flow; creates seal btw cylinder and machine

Question 7

What is the pin index safety system?

Answer 7

used with e-cylinders
medical gases to ensure correct cylinder being fitted to yoke w/ specific pins
Do not change/move safety pins; check pins; keep cylinder attached to prevent pin damage

Question 8

What is the cylinder pressure guage and regulator?

Answer 8

gauge measures gas pressure in tank
pressure is read when tank is turned on
regulators reduces pressure from as high as 2200 PSIG to 45-60PSIG

Question 9

What is the o2 flush valve?

Answer 9

direct tube that connects o2 source to breathing circuit (bypasses flow meter and vaporizer)
gives 35-70L/min flow (45-60psi) of pure oxygen as a straight shot
can be used to flush anesthetic agent from lines
never use with baine - too high pressure can pressure damage to small animals
can ignore and obtain similar effect by turning up oxygen flow meter

Question 10

What is the o2 flow meter assembly?

Answer 10

controls, measures and indicates rate of flow of gas passing through it
control knob is color coded for each gas (white = o2; blue = n2o)
opening stem inc flow rate, closing dec rate
specific for each machine and calibrated for 20C, 101.3 kPa

Question 11

How do we correctly read a flow meter?

Answer 11

read from TOP of bobbin (screw shaped)
Read from MIDDLE of ball

Question 12

What are o2 alarms?

Answer 12

standard in newer machines
alarms sounds if too high pressure, sustained high pressure or negative pressure detected

Question 13

What is the low pressure system?

Answer 13

everything located downstream of flow meter
Vaporizor or precision plenum vaporizor
delivers a set partial pressure of inhalant gas; and mixes with O2
has lock and key system that matches anes. bottle to ensure only one agent used
*never tip
SVMA bylaws vaporizers must be serviced every 2 years but 1 year is recommended

Question 14

If we tip the anesthetic machine, what might happen to the low pressure system?

Answer 14

liquid anes gas may enter the lines = unpredictable amount of gas delivered to patient next time it is used
if tipped have machine services prior to next use

Question 15

How is the vaporizer and inhalant drugs color coded?

Answer 15

Halothane = red
Isoflurane = Purple
Sevoflurane = Yellow
Desflurane = Blue

Question 16

What is the common gas outlet?

Answer 16

Where mixture of oxygen and inhalant are delivered into the breathing system
usually has a valve that allows switching btw non-rebreathing and breathing circuits

Question 17

What is the pop-off valve?

Answer 17

aka APL valve, exhaust valve
pressure relief valve
allows excess gas to escape system
Opens at a pressure of 5psi
prevents damage to the vaporizer and flow meters if there is outlet obstruction
keeping closed will cause pressure in system to build - patient can’t breathe, barotrauma
Always keep open
always check to make sure not obstructed
only close to manually ventilate or f auto-ventilating

Question 18

What is the rebreathing bag?

Answer 18

resevoir bag - patient breathes from the bag
the average tidal volume is 10-15ml/kg (SA like kittens on higher end), lower is COPD or other airway disease
Converts to working volume of 1 -1.5L/10kg when selecting size of bag
As patient draws from bag, can use to monitor RR, depth and to ventilate

Question 19

How do you know what size a breathing bag is? How do you wash it?

Answer 19

size is indicated on bag
need to be rinsed with soapy water and hung to dry btw every ptient

Question 20

What is the breathing circuit manometor?

Answer 20

measures pressure in breathing circuit
0-2cm H2O when breathing spontaneously
Max 10-15cm H2O (K9/fel(
Man 20cm H2O (eq/boc) (lower in textbook to allow for response and prevent trauma)
higher pressures will cause lung damage, pneumothorax

Question 21

What is soda lime and what does it do?

Answer 21

calcium and sodium hydroxide
specific to removing CO2 from a breathing circuit (so patient is not breathing in the excess CO2)
exhaled gas flows through one-way valve to co2 canister > scavenger (soda lime) selectively absorbs CO2 that was breathed out > O and inhalant gas that was not absorbed continues to patient or exhaust
only used in rebreathing systems

Question 22

When do we change soda lime?

Answer 22

inc CO2 build-up in patient, color change, lack of heat in canister, hardness of granules (dried out granules don’t absorb)
time of function
gain of 50g in canister (weight before attaching to machine)

Question 23

How do we determine when soda lime is exhausted?

Answer 23

color change w/ pH indicator
change when 2/3 of canister has changed color
not reliable on its own bc only works with packed properly granules, reverts to white if not used for awhile

Question 24

What are waste anesthetic gas?

Answer 24

WAGs - personnel safety concern
nitrous oxide, halogenated anesthetic gases, metabolic by-products of anesthetic gases
measured in parts per million (ppm) - number of molecules of iso per 1 mil molecules of air
Controlled by avoiding spills, testing equipment for leaks, exhaust and scavenging of WAGs

Question 25

What is a wast anesthetic gas scavenger, how do they work?

Answer 25

They remove WAGs from work space - attaches at pop-off valve (or re-breathing) or tail of reservoir bag (non-rebreathing)
Collects gas leaving circuit and 1. disposes it outside the building (active or passive systems) or 2. gases through activated charcoal canisters before releasing into room air

Question 26

When do we replace WAGs?

Answer 26

q12h or gain of 50g
works best w/ higher pressure air flow
diff from sodalime which only removes CO2
activated charcoal scavenging cannister on anesthetic machine

Question 27

Does the exhaust system need a charcoal system attached?

Answer 27

can be with or without

Question 28

What happens if the scavenger or WAG is blocked?

Answer 28

will prevent gas leaving circuit (same as If leaving pop-off valve closed)

Question 29

What is a patient breathing circuit?

Answer 29

allow cyclic flow to and from patient “breathing”
3 types: open circuit ventilation system, non-rebreathing circuit (including brain), breathing circuit (circle system)

Question 30

What is an open circuit breathing system?

Answer 30

gas from atmosphere alone
literally just an ambu-bag or breathing bag

Question 31

What is a non-rebreathing circuit?

Answer 31

all exhaled gas is dumped (therefore no CO2 canister required
patient always get fresh gas flow (FGF)
bain coaxial circuit is most important in vet mrf
fresh gas port goes directly to patient; exhaled gas goes to the reservoir bag (past open pop-off valve), then out of the machine.
Does not req a soda lime
req higher O2 flow rates to push expired gases down exhaust tube

Question 32

What is a rebreathing circuit?

Answer 32

circle system; or semi-closed circuit
some exhaled gas goes past to patirnt

Question 33

How do rebreathing circuits work by?

Answer 33

operates using system of one-way valves
gas exits vaporizer > enters patient via FGF port > patient exhales > gas enters one-way exhaust port > goes to reservoir bag > excess pressure released from pop-off valve > air from resevoid bag is rebreathed by patient > air goes past b

Question 34

when might we NOT use the rebreathing circuit?

Answer 34

not appropriate for <3kg

Question 35

What is the universal F tube?

Answer 35

a rebreathing tube, does look a lot like a bain but has an exhaust port

Question 36

What is the difference btw nonbreathing and breathing?

Answer 36

Non-rebreathing: ex. bain, ain in>out, all CO2 and inhalant is exhaled, each breath is fresh O2 and inhalant, higher flow rates (~150ml/Kg/min) = $$$
less dead space, less resistance to spontaneous breathing
Rebreathing: ex. circle, exhaled CO2 (some inhalant gas is captured), majority of inhalant is rebreathed thru system, lower O2 flow rates (~30ml/kg/min) lower $, use w/ >5kg
conserves temp and humidity

Question 37

What is the difference of flow rates with non-rebreathing and breathing circuits?

Answer 37

non: bain, req high flow, O2 flow rate 150-200ml/kg/min
Rebreath: circle, req lower flow rate, O2 rate 30ml/kg/min

Question 38

What is an adaptor?

Answer 38

connects breathing tubes to ETT
usually has adaptor to capnograph (measures end-tidal CO2)

Question 39

What is the heat and moisure exchanger?

Answer 39

nice to have
loc btw patient and circuit
prevents moisture from entering circuit while warming and humidifying gases to patient