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Anesthesia > Anesthesia Machine and Breathing Systems > Flashcards

Anesthesia Machine and Breathing Systems Flashcards

1
Q

Basic Machine Schematic

A 
Oxygen cylinder
Cylinder pressure gauge
pressure reduction valve
flowmeter
vaporizer
fresh gas inlet
breathing circuit 
patient
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2
Q

Compressed gas

A

Oxygen- absolutely necessary
delivering anesthetic gas in air (21% O2) would lead to hypoxemia due to hypoventilation and V/Q mismatch induced by anesthetics themselves
30-35% O2 minimum acceptable for people and small animals

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3
Q

Metabolic requirement for oxygen

A

5-10 mL/kg/min

50-100 mL/min in a 10 kg dog
Minimum O2 flow required

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4
Q

Other medical gases

A

Nitrous oxide

Medical air

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5
Q

Oxygen sources

A

Cylinder
Liquid (cryogenic oxygen)
Oxygen concentratior

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6
Q

E cylinder

A

usually single, attached directly to anesthesia machine via yoke
Most common in small animal general practice
Capacity = 660 L
filled to pressure of 2200 psi
boyles law may be used to determine the remaining gas in the tank

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7
Q

H cylinder

A

Often in banks, supply for central O2
Capacity= 6600 L
filled to pressure of 2200 psi
boyles law may be used to determine the remaining gas in the tank

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8
Q

Compressed gas

A 
Cylinders are color coded
Oxygen= green
Nitrous oxide = blue
Medical air = yellow
Other safety mechanisms in place to prevent delivering wrong gas
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9
Q

Tank safety

A

never leave an unsecured tank sitting upright
E in rack/rolling cage
H anchored to wall or in transport cart with chain
May explode if dropped or falls over-can become projectile
To avoid fire (heat created as gas expands)- clean oils from hands/tank
open valve slowly
open and close valve before attaching to machine to remove dust from connecting port

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10
Q

Pressure gauges

A

Used to measure cylinder pressures, pipeline pressures, anesthetic machine working pressures, and pressure within breathing system
Cylinder pressure usually in psi
breathing system pressure in cm H2O

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11
Q

Calculate remaining O2

A

2200/660 = psi left on tank/x L

Minutes = x liters/flow L/min

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12
Q

N2O cylinders

A

N2O exists in both a gaseous and liquid form in tank - gauge only reads gas pressure
Therefore it is not possible to calculate the amount of gas remaining based upon pressure if liquid N2O remains

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13
Q

Safety systems

A 
Color coded tanks
labelling
diameter index safety sistem
pin index safety system
quick connectors 1
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14
Q

Diameter index safety system

A

non-interchangeable gas-specific threaded connection system

used universally by all equipment and cylinder manufacturers

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15
Q

Pin index safety system

A

Gas-specific pin patterns that only allow connections between the appropriate cylinder tokes and E tanks
Commonly found on tokes mounted to anesthesia machines, also some cylinder specific regulators/flowmeters

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16
Q

Quick connectors

A

Manufacturer specific
Facilitate rapid connecting and disconnecting of gas hoses
useful for multipurpose work areas

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17
Q

Regulator

A

Pressure reducing valve
Decreases tank pressure to a safe working pressure which is supplied to the flowmeter
Prevents pressure fluctuations as the tank empties

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18
Q

Flowmeter

A

Controls rate of gas flow through the vaporizer (L/min)
Gas enters at bottom at 50 psi and exits at top at 15 psi
Tapered glass tube with moveable float- narrow at bottom, wider at top
Single or double taper- double=more accuracy at lower flow
Calibrated for 760 mmHg and 20C
Reduces gas pressure form 50 psi to 15 psi
gas specific!
if there are multiple flowmeters, O2 should be on the far right (downstream) to prevent delivery of a hypoxic gas mixture

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19
Q

Floats

A

Can be ball or bobbil

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20
Q

Where do you read flow

A

Middle of ball

Top of bobbin

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21
Q

Quick flush

A

Delivers O2 from the intermediate pressure area of the machine
Bypasses vaporizer- contains NO anesthetic agent
Delivers gas at rate between 35-75 L/min directly to patient circuit
Appropriate use: quickly decrease anesthetic gas % in the circuit- emergency, recovery
This is pure O2 that has bypassed the vaporizer

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22
Q

Quick flush complication

A

pneumothorax
small circuit
high pressure
small patient

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23
Q

Anesthetic vaporizers

A

change liquid anesthetic into vapor
deliver selected % of anesthetic vapor to the fresh (common) gas outlet
-volumes percent

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24
Q

Inhalants- vapor

A

gaseous state of substance that is liquid at ambient temp and pressure
Halothane, isoflurane, sevoflurane, desflurane

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25
Q

Inhalants-gas

A

exists in gaseous state at ambient T and P

N2O, Xenon

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26
Q

Vapor pressure

A

Pressure exerted by vapor molecules when liquid and vapor phases are in equilibrium
Depends on temperature- increases with increasing temperature
Inversely related to boiling point

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27
Q

Saturated vapor pressure

A

Vapors have a maximum administration percentage
vapor pressure/barometric pressure
ex: iso 32%
vaporizers needed to reduce this to clinically useful doses

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28
Q

Modern vaporizers

A 
agent specific 
concentration calibrated
variable bypass
flow over
out-of-circuit
high resistance
compensated for temperature, flow, and back pressure
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29
Q

Anesthetic vaporizers

A

a specific concentration is created by variable bypass system, where fresh gas flows over a reservoir of liquid anesthetic and mixes with carrier gas

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30
Q

VOC vaporizers-precision

A

all modern vaporizers are out of circuit (VOC)
carrier gas is from flowmeter
anesthetic % is known = precision vaporizer

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31
Q

VIC vaporizers- non-precision

A 
in the past, vaporizers were in the circuit (VIC)- non precision
Glass jar containing wicking material
increase surface area for vaporization
ensures saturation with anesthetic gas
Variable bypass

Carrier gas is patients expired gases
cannot produce a known anesthetic %
not temperature compensated
not currently recommended

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32
Q

Modern vaporizers compensate for

A

temperature between 15-35 C
flow rate between 0.5 and 10 L/min
Back pressure associated with positive pressure ventilation and use of flush valve

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33
Q

Temperature compensation

A

Achieved by using materials that are efficient heat conductors
also mechanical thermocompensation
alters the amount of carrier gas directed through the bypass and vaporizing chambers
has a thermal element made of a heat-sensitive metal that reliably expands and contracts based on temperature

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34
Q

Flow rate compensation

A

achieved by ensuring saturation of gas moving through vaporizing chamber
use of wicks, baffles, and spiral tracks that facilitate vaporization

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35
Q

Back pressure

A

Can occur during positive pressure ventilation or use of flush valve
may increase vaporizer output if compensation mechanisms not present
modern vaporizers use various mechanisms to prevent this from happening

36
Q

Vaporizer styles

A

ohmeda tec 5
drager vapor
penlon sigma

37
Q

Desflurane vaporizer

A

Boiling point (23.5C) is close to room temperature
Electric heated vaporizer required
-desflurane maintained in gaseous form
-blends with fresh O2 to achieve vaporizer setting
Common in human med bit not vet bc more expensive

38
Q

Vaporizers

A

filled using screw cap port or agent-specific keyed filler port
prevents filling with wrong agent
Require no external power (except desflurane)
Routine maintenance is required and must be performed by a qualified technician
Mounted on a back bar on the machine
cannot be tipped- must be emptied before transporting

39
Q

What would happen if filled with wrong agent

A

Depends on vapor pressure and potency of each agent
iso in sevo vaporizer could produce lethal concentration (higher vapor pressure AND higher potency)
Drain and run 1L/min O2 until completely dry

40
Q

Vaporizer tipped

A

anesthetic may enter the bypass channel and deliver a high concentration
Run 1L/min O2 through machine with vaporizer off

41
Q

Common gas outlet

A

where gas exits the vaporizer
connected by a hose to the fresh gas inlet
hose must be connected so that fresh gas flows to the breathing circuit
connects to either rebreathing or non-rebreathing system

42
Q

Re-breathing system

A

rebreathing expired gases after gone through co2 scavanger
Circle
Universal F

43
Q

Non-rebreathing system

A

Mapleson A-F

most common= bain (modified mapleson D), mapleson F

44
Q

Dead space

A

anatomic/mechanical
breathing tubes in a circle system do not constitute dead space because the flow is unidirectional (no rebreathing)
this is why breathing tubes may be very long without increasing dead space
dead space in non-rebreathing system consists of the space between the fresh gas flow inlet and the patient - differs depending on mapleson type

45
Q

Anatomic dead space

A

airway structures that do not participate in gas exchange

oral cavity, larynx, trachea, bronchi

46
Q

Mechanical dead space

A

the portion of the anesthesia circuit where bidirectional flow is occuring (rebreathing of exhaled gases)
if excessive, this may cause an unsafe increase in inspired CO2
face mask
endotracheal tube extending past patients incisors (outside of mouth)
capnograph or other adapters
Y piece

47
Q

Rebreathing system components

A

fresh gas input and O2 flush
unidirectional valves (inspiratory and expiratory)
Breathing hoses (circle or universal F)
CO2 absorber
Adjustable pressure limiting valve (pop-off)
reservoir bag

48
Q

Rebreathing system

A

one way gas flow (circular)
inspiratory and expiratory breathing limbs
rebreathing is prevented by inspiratory ad expiratory valves
CO2 absorber removes CO2 from expired gases
patient rebreathes gases via the inspiratory limb
Composed of exhaled gases after CO2 removal and fresh gas flow

49
Q

Rebreathing system advantages

A

lower fresh gas flow rate required
patient breaths warm, humidified gases (re breaths)
saves money
decreases environmental pollution

50
Q

Rebreathing system disadvantages

A

higher resistance to breathing due to valves
changes in anesthetic gas concentration occur slowly d/t lower fresh gas flow
more components -> more potential for leaks

51
Q

Rebreathing system

A

One way or unidirectional valves- inspiratory; expiratory
O2 flush valve- bypasses vaporizer, dilutes anesthetic gas in breathing system and reservoir bag, delivers O2 directly to the breathing system at high pressure and flow 35-75 L/min O2
Disconnect patient from circuit before activating to avoid barotrauma
Fresh gas inlet
shared connection between rebreathing and non rebreathing systems

52
Q

Rebreathing system- cont

A

adjustable pressure limiting valve or pop-off
limits pressure build up on breathing system
should pop off at 305 cm H2O
should always be open unless- checking machine for leaks before use, administering positive pressure ventilation (manual or mechanical)
Closed APL valve –> increases pressure in breathing system as fresh gas flow continues into circuit with no exhaust -> cardiorespiratory arrest and death
breathing circuit pressure gauge
should be 0 +/- 1 with spontaneous patient breathing
exception- leak check, positive pressure ventilation

53
Q

re breathing system carbon dioxide absorber

A

soda lime most commonly used
assembly contains canister to hold soda lime, 2 ports for connecting breathing tubes, fresh gas inlet, +/- unidirectional valve and bag mounts
soda line is calcium hydroxide with small amount of sodium hydroxide
also contains ethyl violet which changes color from white to purple when granules are exhausted

heat and water is produced from reaction between CO2 and soda lime
color change will be seen when active- this does not mean that the absorbent is exhausted
When filling canister do not pack tightly
may cause leaks if present on gaskets- check when machine has an unidentified leak

54
Q

Signs of CO2 absorbent exhaustion

A

inspired CO2 is >1-2 mmHg on capnograph (=rebreathing), increased PaCO2 on blood gas
Patient signs
increased RR (attempting to compensate for increased inspired CO2)
increased HR and BP (CO2 -> sympathetic stimulation)
Red mucous membranes (due to CO2 induced vasodilation

55
Q

Reservoir bag

A

functions: inspiratory reserve for patient
administering positive pressure ventilation
allows anesthetist to monitor ventilation

Calculation of bag size for small animals
tidal volume (~15 mL/kg) x 6
round up
For horses usually 30L or 20L ventilator capacity

56
Q

Rebreathing system- oxygen flow rates

A

many different flow rates can be used
all are safe for patient as long as greater than metabolic O2 requirement (5-10 mL/kg/min)
chosen based on goals and practicality (flow meter is a limitation)

57
Q

Typical O2 flow rates

A 
Small animals (<50kg)
induction and recovery 50-100 mL/kg/min
maintenance 20-50 mL/kg/min

Large animals
induction and recovery 20-50 mL/kg/min
maintenance 10-20 mL/kg/min

58
Q

Non-rebreathing system- components

A

Fresh gas
non-rebreathing tubes
APL valve (bain) or open/close valve (mapleson F)
Reservoir bag

NO soda lime canister, unidirectional valves

59
Q

Non-rebreathing system- advantages

A

light, minimal dead space, minimal resistance to ventilation (use for small patients <3kg)
concentration of anesthetic gas changes rapidly due to high fresh gas flow and small circuit volume
fewer components = fewer potential for leaks

60
Q

Non-rebreathing system- disadvantages

A

requires high gas flow rates
patient breaths cold and dry gas d/t lack of rebreathing
more expensive
increases environmental pollution

61
Q

Non rebreathing system oxygen flow rates

A

must be high as this is the mechanism for preventing rebreathing of CO2
should be 2-3x minute ventilation
~300 ml/kg/min

62
Q

Endotrachial tubes and intubation

A

maintain patient airway
administer O2, deliver inhalant anesthetics
provide positive pressure ventilation
protect airway from foreign material (regurgitation, other fluids and solids)
apply tracheal or bronchial suction
Other: decreases environmental contamination with volatiles anesthetics if cuff is properly inflated

63
Q

Routes of intubation

A

Oral
Nasal
Tracheal
Pharyngotomy

64
Q

Types of ETT

A 
PVC, rubber, silicone
Cuffed/uncuffed
Murphy
Cole
Wire-reinforced
65
Q

Cuffed ETT

A

protects airway and environment, but may not be indicated for certain patients (v small, birds)
Cuff must be inflated carefully to avoid tracheal trauma

66
Q

Cuff types

A

high volume- low pressure (preferred for tracheal protection)
high pressure-low volume

67
Q

Murphy ETT

A

can be cuffed or uncuffed
has a murphy eye that allows gas flow if end of tube is obstructed
most common ETT in veterinary anesthesia

Pilot balloon and valve
size marker in mm (ID=internal diameter)
cm marks to determine length of tube in patient

68
Q

Cole ETT

A

uncuffed

used commonly in avian patients, has a shoulder that seals against the glottis

69
Q

Wire reinforced (armored) ETT

A

used to prevent collapse of tube lumen when patients are placed in extreme flexion (usually ophtho procedures)
cannot use for MRI (contains metal)

70
Q

ETT sizes

A

tubes with larger radius and shorter length will have less resistance to gas flow
Radius has the larges effect (poiseuille’s law)

71
Q

Preparing to intubate

A

Determine size you think +/- 1 size (based on weight, breed, species, trachial palpation)
inflate cuff to check for leaks
ensure ETT is clean and dry
Cuff syringe
Tube tie (tie around tube, then above muzzle or behind ears)
+/- special supplies (stylet, mouth gag, capnograph, etc)
Laryngoscope
miller/macintosh

72
Q

Laryngoscope

A

Makes intubation safer and easier
allows visualization of airway
apply light pressure to base of tongue, rostral to epiglottis
do not place the blade of it on epiglottis- could cause damage

73
Q

ETT cuff inflation

A

procedure requires 2 people
connect patient to circuit with O2 flowing
close the adjustable pressure limiting (APL) valve using the safety system (push rather than screw closed)
squeeze the reservoir bag to a total pressure of 20 cm H2O
listen at the patients mouth for ai escaping the trachea. If you do not hear a leak at the initial squeeze then no air is needed in the cuff
If a leak is heard at 20 cm H2O add air to the ETT cuff just until no leak is heard
Open the APL valve

74
Q

ETT cuff hints

A

do not inflate cuff without first checking to see if there is a leak
exception ruminants- air should be added before any movement d/t high risk of regurgitation
Caution when moving patients with inflated ETT cuff
Disconnect from circuit before moving
Tracheal tears are not uncommon in cats due tp moving patient with cuff inflated and breathing tubes connected

75
Q

Complications of intubation- laryngeal damage

A

laryngospasm, inflammation, edema, hemorrhage

76
Q

Complications of intubation- tracheal damage

A

over-inflated cuff
moving or twisting patient with inflated cuff
may lead to mucosal damage, tracheal rupture (-> SQ emphysema, pneumomediastinum, etc), persistent tracheal membrane (avian)

77
Q

Complications of intubation- ETT obstruction

A

secretions (mucus most common), cuff over inflation

78
Q

Complications of intubation- endobronchial intubation

A

ETT to far into airway
must measure tube at time of intubation, ETT should not extend past thoracic inlet
leads to hypoxemia +/- hypercapnia

79
Q

Complications of intubation- ETT inhalation or ingestion

A

if patient chews tube (usually upon recovery)

do not wait to long to extubate

80
Q

scavenging waste gases

A

necessary due to detrimental effects of excess waste gas (volatile anesthetics and N2O) on personnel
reproducing effect most serious
also headaches, nausea

involves collecting and transporting waste gases from the anesthetic machine to a safe disposal area
active or passive

81
Q

Waste gases

A

Exposure to volatile anesthetic agents should be < 2 ppm
100%=1mil ppm
1%= 10k ppm
must be >125 ppm to smell it `

82
Q

Minimize exposure

A 
scavenge at all times- keep patient attached to machine during recovery so they are not breathing agent into room air
ensure that the machine has no leaks- leak test before use
use ETT with properly inflated cuff
avoid mask or chamber inductions
check for tight fittings
use low O2 flows 
maintain appropriate room ventilation
use keyed systems for filling vaporizers
83
Q

scavenging waste gases- passive

A

no vacuum
exhaust directly to atmosphere (via window or hole in wall)
F air canister
absorbs halogenated agents (anesthetic vapors)
does not scavenge N2O

84
Q

scavenging waste gases- active

A

piped vacuum (white quick connector)
most common
central vacuum capable of handling high flows

85
Q

F air canister- advantages

A

absorbs anesthetic vapors
does not release to atmosphere
portable

86
Q

F air canister- disadvantages

A

does not absorb N2O
flow limited
added resistance
Must be discarded when anister has gained 50g

87
Q

Other courses of pollution

A

capnograph (removes sample from breathing circuit) needs to be scavenged
Face mask and chamber inductions
Recovery areas
esp large animals
horses exhale a lot of volatile agent in recovery stall
Volatile agent spills
clean immediately, place contaminated material in a well ventilated area for disposal

Anesthesia (12 decks)

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