Anesthetic equipment Flashcards
What are the two functional systems of the anesthetic machine
Life support- oxygen and everything associated with breathing and assisted ventilation
Inhalant drug delivery- getting a safe amount of gas into the patient to keep them under
What are the basics continuous machine designs
High pressure system
Intermediate pressure system
-Flow metres
Low pressure system
What are high pressure anaesthetic machines
High pressure supply of gasses (supplied by cylinders or pipelines)
Pressure gauges (regulators) to control flow of gasses into the machine
What is the low pressure anaesthetic machine
Vaporizer to create accurate mix of gasses at known concentration
Breathing circuit- to deliver to patient
What is the flow through a bane anaesthetic machine
Tank
Tank pressure gauge
Pressure reducing valve
Line pressure gauge
Flow meter
Vaporizer
Patient
Excess into charcoal canister
What is the flow of anaesthetic in a rebreathe system
Tank
Tank pressure gauge
Pressure reducing valve
Line pressure gauge
Flow meter
Vaporizer
Inhalation valve
Y-piece
Patient
Exhalation tube
CO2 canister
Pressure manometer
to scavenger
High pressure system is used for
O2 N2O
High pressure system can have what oxygen supply
Pipeline or cylinders
pipeline oxygen supply for high pressure systems are
50 psi (same as normal working pressure of most machines)
Tanks are located elsewhere in building
Cylinder in a high pressure system is
Oxygen is supplied around 2000 psi (needs to be reduced to about 45 psi when entering anaesthetic machine)
What is a yoke assembly
Hanger yoke assembly- connects cylinder to machine; ensures unidirectional gas flow; creates seal b/w cylinder and machine
Pin index system is
Used with E-cylinders
Medical gasses to ensure correct cylinder is being fitted to yoke
Pins in yoke assembly match to holes in a specific cylinder– ensures correct gas is being used
Do not change/move safety pins; check pins; keep cylinder attached to prevent pin damage
Cylinder pressure gauge and regulator is
Gauge measures gas pressure in tank
Pressure is read when tank is turned on
Regulator reduces pressure form as high as 2200 PSI to 45-60 PSI
Oxygen tanks can be what colour
White
Green
White + green
White + black (UK, Europe)
N2O tanks are what colour
Blue
Intermediate pressure systems have
O2 flush valve
O2 flow meter assembly
O2 alarms
O2 flush valves for intermediate pressure systems are
Direct tube that connects the O2 source to the breathing circuit (bypasses vaporizer)
Gives 35-70 L/min flow (40-60 psi) of pure oxygen as a “straight shot”
Can be used to flush aesthetic agent from lines
Never use with a Baine
Too high pressure can cause pressure damage to small animals
Can ignore and obtain similar effect by turning up oxygen flow meter
O2 flow meter assembly of intermediate system
Controls, measures and indicates rate of flow of gas passing through it
Control knob is colour coded for each gas (white=O2; blue=N2O)
Opening stem increases flow rate; closing decreases rate
Specific for each machine and calibrated for 20*C, 101.3 kPa
How to correctly read a flow meter
Read from TOP of bobbin; MIDDLE of ball
O2 alarms are in what machines and do what
Standard in newer machines
Alarm sounds if too high pressure, sustained high pressure or negative pressure detected
Low pressure system is located where
Everything located downstream of the flow meter
Vaporizer is and used for
Aka precision plenum vaporizer
Delivered a set partial pressure of inhalant gas; and mixes with oxygen
Vaporizers are specific to one anaesthetic gas (based on vapour pressure; note colour coding)
Has lock and key system that matches anaesthetic bottle to ensure only one agent used
SVMA byways vaporizers must be serviced every 2 years (recommended every year)
Why cant you tip the vaporizer
Liquid anaesthetic gas may enter lines= unpredictable amount of gas delivered to patient next time it is used
If tipped have machine services prior to next use
What colour does each vaporizer indicate
Halothane = red
Isoflurane = purple
Sevolflurane = yellow
Desflurane = blue
Common gas outlets are
Where the mixture of oxygen and inhalant are delivered into the breathing system
Usually has a valve that allow switching between non-rebreathing and rebreathing circuits
pop off valve is and used for
AKA APL valve, exhaust valve
Pressure relief valve
Allows excess gas to escape the system
Opens at a pressure of 5 psi
Prevents damage to the vaporizer and flow meters if there is outlet obstruction
Keeping closed will cause pressure system to build
Always keep open
Always check to make sure it is not obstructed
Only close to manually ventilate or if auto-ventilating
What happens if you keep the pop off valve closed
Keeping closed will cause pressure system to build
Patient cant breathe
Barotrauma
Rebreathing bag is
Reservoir bag-patient breathes from the bag
You want the bag to be big enough to fill patients lungs during an inhalation, but not so large that you can’t visualise respiration
Size determination based roughly on weight of the patient (using tidal volume)
How is the rebreathe bag useful
As patient draws from bag, can use to
Monitor resp rate
Monitor depth of breathing
Ventilate
What does the rebreathe bag size do
Comes in a variety of sizes- 300ml to 35L (LA)
Size is indicated on bag
Need to be rinsed with soapy water and hung to dry between every patient
Soda lime (calcium and sodium hydroxide) is used for
Specific to removing CO2 from a rebreathing circuit (so patient is not breathing in the excess CO2)
Exhaled gas flows through one way valve to CO2 canister → scavenger (ie. soda lime) selectively absorbs CO2 that was breathed out→ oxygen and inhalant gas that was not absorbed continuous to patient or exhaust
Only used in rebreathing system (circle) system
When should you change the soda lime
Increased CO2 build up in patient
Colour change
Lack of heat in canister
Harness of granules (dried out granules don’t absorb)
Time in function
Gain of 50g in canister (weight before attaching to machine)
How can the capnograph let you know the soda lime needs to be changed
Base line will be above 0
Why does the colour of soda lime change and when is this helpful
Colour change is with pH indicator
Change when ⅔ canister has changed colour
Not reliable on its own because
Only works when granules are “packed properly”
Reverts to white if not used for a while
Waste anesthetic gas is
Personal safety concern
Nitrous oxide, halogenated anesthetic gasses, metabolic by-products of anaesthetic gasses
Measured in parts per million (ppm)
Number of molecules of iso per 1 million molecules of air
What is waste anesthetic gas controlled by
Avoiding spills
Testing equipment for leaks
Exhaust and scavenging of WAGs
What does the waste anaesthetic gas scavenger do
Scavenger remove waste anesthetic gasses from work space
Attaches at pop-off valve (rebreathing) or tail of reservoir bag (nonrebreathing)
Collects gas leaving circuit and
Disposes it outside the building (active or passive system)
Or
Gasses through activated charcoal canisters before releasing into room air
Activated charcoal scavenging canister on anaesthetic machine
Exhaust system with or without charcoal system attached
Why is activated charcoal used as a gas scavenger
Convenient
Requires frequent replacement (q 12h or gain of 50g)
Works best with higher pressure air flow
Different form soda lime which only removes CO2
What do you do to scavenge waste aesthetic when not using charcoal
Can be active (fan moves air) or passive (pushed out by pressure placed into system)
If blocked, will prevent gas leaving circuit (same as if leaving pop-up valve closed)
Patient rebreathing system allows what
Allow cyclic flow
To and from the patient
Aka breathing
3 types of breathing systems
Open circuit ventilation system
Non Rebreathing circuit (includes Bain)
Rebreathing circuit (aka circle system)
Open circuit breathing system does what
Gas is from atmosphere alone
Ambu-bag
Non rebreathing circuit works by
All exhaled gas is dumped (therefore no CO2 canister required)
Patient always get fresh gas flow (FGF)
Bain coaxial circuit is most common in vet med
When and why is the non rebreathing circuit used
Used in small patients <10 kg (must use if less than 3kg)
Less dead space and resistance to breathing which is preferred
Fresh gas port goes directly to patient; exhaled gas goes to the reservoir bag (past open pop-up valve), then out of the machine
Does not require soda lime
Requires higher O2 flow rates to push expired gasses down exhaust tube
Rebreathing circuit is
Aka circle system; or semi-closed circuit
Some of the exhaled gas goes back to the patient
Operates using system of one way valves
How does a rebreathing system work
Gas exits vaporizer → enters patient via FGF port→ patient exhales→ gas enters oneway exhaust port→ goes to reservoir bag→ excess pressure released from pop-off valve→ air from reservoir bag is rebreathed by patient→ air goes past soda lime canister to remove CO2→ pickles up additional fresh gas before entering patient
When do you use a rebreathing system
Typical hoses are used for patients over 10kg
There are pediatric hoses available fo 3-10kg
Not appropriate for <3kg
Non rebreathing system basics
Ex. Bain
Air in → air out
All Co2 and inhalant exhaled
Each breath is fresh O2 and inhalant
Higher flow rates (~150 ml/kg/min)= increased cost
Less dead space
Less resistance to spontaneous breathing
Rebreathing system basics
Ex. circle
Exhaled CO2 (some inhalant gas ) is captured
Majority of inhalant is rebreathed through the system
Lower O2 (~30 ml/kg/min) = decreased cost
Use with >5kg patients
Getting more common
Conserves temp and humidity
Flow rate with rebreathing system
Circle
Requires lower flow rate
O2 flow rate of 30 ml/kg/min
Flow rate with non rebreathing systems
Bain
Requires higher flow rate
O2 flow rate of 150-200 ml/kg/min
Adapter on systems are
Connect breathing tubes to endotracheal tube
Usually has an adaptor to capnograph (measured end-tidal CO2)
Heat and moister exchanger is
Nice to have
Located between patient and circuit
Prevents moisture from entering the circuit while warming and humidifying gases to the patient.
