Anaesthetic equipment Flashcards
What gas can be supplied? 3
Oxygen, NO and medical air
What is the ‘PISS’ system?
Pin-index safety system on E-sized cylinders (ensures safety of pressurised gas). There is a washer (the Bodok seal) between the cylinder and the yoke.
Describe an oxygen cylinder
(Black) or white cylinder
White top
137 bar (13700kPa)
guage pressure indicates volume left in cylinder
What is a blue cylinder?
NO gas
4.4 bar (4400kPa)
Guage pressure does NOT indicate volume left
Weigh cylinder
Gas present (L) = ((net-tare) weight (g) * 22.4)/44
Define MHRA
Medicines and Healthcare products Regulatory Agency
Describe a medical grade air cylinder
Grey cylinder Black/white quarters on top Supply pressure depends on use Advanced surgeries Mostly N, less O2.
Why use medical gas pipelines?
(Gas supplied from source outside building)
Safer and more economical
What are the terminal units of medical gas pipelines called?
Schrader valves. Terminal units are colour coded like the cylinders. These are non-interchangeable. Hoses connecting valves to the anaesthetic machine are colour coded.
What is an oxygen concentrator ?
extracts oxygen from the air but needs a source of electricity. Max. O2 concentration is 95%. Smaller practices usually.
What does an anaesthetic machine consist of?
Gas supply Pressure gauges Pressure regulators Flowmeters Vaporisizers Other features (emergency O2 flush, common gas outlet)
What does a pressure regulator do?
decreases pressure from the cylinder to be used in the patient.
Describe pressure guages
For O2 - this indicates amount left in cylinder
For NO - need to weigh cylinder
What do pressure regulators/reducing valves do?
Reduce cylinder pressure to a safer level (around 4 bar)
Keep pressure constant
Positioned between cylinder and machine
What do flowmeters do?
- Measure flow rates of gases (indicated by a bobbin or ball bearing floating in a transparent glass or plastic tube. Read flow rate on the top of the bobbin or the middle of the ball bearing)
- Calibrated for a single gas
- Flow controlled by turning a knob on front of flowmeter
- Knobs are colour-coded for each gas
What do low oxygen pressure alarms do?
whistle either powered by low pressure oxygen or NO cylinder
What does the emergency oxygen flush do?
The O2 flush valve enables high flow of O2, bypassing the ‘back bar’ (therefore usually bypassing the vaporiser)
What is a pressure relief valve for?
so that if something blocks the outlet, the pressure does not rise so far that the machine comes apart.
What do compressed oxygen outlets do?
drive the ventilator (not electricity)
What do vaporisers do?
vaporise liquid (volatile) anaesthetics
Deliver known concentrations of anaesthetic
Calibrated for one agent only
Accurate over a range of temperatures and flows
What affects administration through a vaporiser?
Flow through the vaporising chamber Efficiency of vaporisation Temperature Time Gas flow rate Carrier gas composition
What is isoflurane TEC 3?
Agent specific filling (Fraser Sweatman pin safety system, prevents mixing of agents within the vaporiser)
Must not be tipped over (uncontrolled output of anaesthetic agent may result)
What is TEC4?
Similar to TEC3 but…has an anti-spill feature and an interlock facility (to prevent 2 vaporisers being used simultaneously)
What is a penlon vaporiser?
More modern. Currently manufactured for isoflurane/sevoflurane
- Temperature compensated
- High resistance
- Agent specific
- Flow compensated
- Back pressure compensated
- Wick: cartridge design for easy cleaning
Aims - Fraser Sweatman safety system - 2
To reduce spillage of volatile agents and prevent mixing of 2 agents inside a vaporiser.
What do sevoflurane bottles do?
They plug directly into the vaporiser and this eliminates spillage.
What is an APL valve?
Adjustable Pressure Limiting Valve - most breathing systems have this
List types of scavenging system - 3
Activated charcoal absorbers
Passive and active scavenging systems
Features - activated charcoal absorbers
Must be replaced every 12 hours
Don’t absorb NO
Gas is adsorbed onto the charcoal
How do active and passive scavenging systems work?
waste gases ducted out of window, pipe or extractor fan to outside. Pollution of atmosphere. Active systems connect to vacuum. Air brake MUST be utilised.
ACTIVE: pumped away int the atmosphere, need an ‘air brake’ to limit suction.
How are anaesthetic breathing systems classified?
Usually classified by how they eliminate CO2 from expired gas:
NON-rebreathing system
Rebreathing system
How does a non-rebreathing system work?
CO2 removed by flow of fresh gas through the system - no expired gas is reused?
How does a rebreathing system work?
CO2 in expired gas is removed by absorption so that expired gas can be re-used.
List examples of non-rebreathing systems - 5
Magill Lack Bain Ayre Humphrey
List 2 examples of rebreathing systems
Circle and to-and-fro rebreathing systems and include a cannister containing CO2 absorbent
What is the Mapelson classification?
It is a functional classification (A-F, C is human only) of non-rebreathing systems. Theoretical efficiency in fresh gas use. Fresh gas flow needed to prevent rebreathing expessed as a multiple of animal’s minute volume (‘circuit factor’)
Define tidal volume (TV)
the volume of gas inspired or expired in one BREATH
Define minute volume (MV)
the volume of air inspired or expired in one MINUTE
How do you calculate the minute volume?
Estimate TV at 10-15ml/kg (use higher value in SA) and multiply this by the RR to obtain MV (MV=TV*RR)
Describe a Magill system (Mapleson A)
Non-rebreathing
Suitable for animals >10kg
Flow rate 1-1.5 * MV (200-300ml/kg/min)
Describe a Lack system (Mapleson A)
Non-rebreathing - 2 types:
- Co-axial (tube within a tube): [Suitable for animals >10kg
Flow rate is 1-1.5* MV (200-300ml/kg/min)]
- Parallel (standard and ‘mini’ versions): [standard version suitable for animals >10kg, mini version for animals <10kg). Circuit factor of 1-1.5]
Describe a T-piece
Ayre’s T piece (and variants)
Suitable for animals <10kg Flow rate of 2.3* MV [500-600ml/kg/min. THis circuit factor is extremely high to ensure gas is not reused.]
Where does fresh gas flow in a Bain system?
fresh gas flows in the inner tube
Describe a Bain system
Non-rebreathing
Mapleson D
Suitable for animals >10kg (but uneconomical)
Flow rate of 2.5-3* MV (500-600ml/kg/min)
What checks need to be made on the breathing system? 6
Connect to anaesthetic machine - close APL valve (remember P means pressure i.e. closed), cover the patient end with you thumb - use oxygen flush to inflate the reservoir bag - watch for leaks - open APL valve
What checks need to be made with co-axial breathing systems?
Check the inner tube also:
turn on the oxygen flow metre, use the red device to briefly cover the inner tube only, if the inner tube is sealed, the flow metre will drop, if there is a leak, the flow metre will remain constant
What is a Humphrey ADE?
A mandelson A, Mandelson D and Manleson E system. Can either allow spontaneous or controlled ventilation.
SPONTANEOUS: valve must be UP, functions as a Mapleson Type A (Magill or Lack), very efficient in fresh gas use
CONTROLLED: valve must be DOWN, functions as a Mapleson type D (Bain), can be used without reservoir bag (Mapleson E) but no facility to scavenge.
How does a Humphrey ADE circuit work?
Universal circuit incorporating a level which allows the circuit to be changed from a Mapleson A to D to E
What flow rate should be used for Humphrey ADE?
CATS: 600ml/min
DOGS (10kg): 2L/min for 10 min then reduce to 1L/min
How are rebreathing systems classified? Examples?
VAPORIZER OUT OF CIRCUIT: circle, Humphrey ADE or to-and-fro.
VAPORISER IN CIRCUIT: Komesaroff machine, Stephens machine
Rebreathing system - advantages - 2
- Much lower fresh gas flows are needed (economy)
- Reaction of absorbent with CO2 produces heat and moisture
Rebreathing system - disadvantages - 3
- exact compositon of inspired gas unknown
- changes in depth take longer
- more expensive
For what animals is a circle system suitable?
Animals >10kg
Describe a coaxial circle
= “universal F circuit”
- inspiratory tube inside expiratory tube
- aids warming and humidification of inspired gases
- resistance increased slightly over parallel circuit systems
- problems if inner (inspiratory) tube is cracked or becomes disconnected.
Describe a to-and-fro system
Same principle as circle system but smaller and more compact.
What are the important practical aspects of using a circular rebreathing system?
- use a higher fresh gas flow initially for first 10 mins (to flush air out so as not to dilute anaesthetics)
- once stable plane of anaesthesia, reduce flow (50ml/kg/min)
- if using NO, don’t exceed a 50:50 mixture
- CO2 absorbent should be changed when half has changed colour
What is important to remember about CO2 absorbers?
if exhausted absorbant is left in the canister, the colour change can reverse, but this doesn’t mean it can be used again
Outline CO2 absorbers:
example
colour change
EXAMPLE: soda lime (potassium/sodium hydroxide)
COLOUR: pink to white or white to violet
REACTION: when it reacts with anaesthetic agent, there is production of CO and compound A, especially risky with very dry soda lime and sevoflurane or desflurane.
“LoFlowSorb” contains calcium hydroxide which eliminates risks associated with compound A and CO.
Green to violet (permanent colour change)
Describe a vaporiser in circuit - 5
- Vaporiser is located in circle circuit.
- Patient breathes through the vaporiser (low resistance)
- Increased ventilation will increase inspired anaesthetic
- Decreased fresh gas flow rate –> increases inspired anaesthetic agent concentration
- very economical in anaesthetic and oxygen use
What is used to place an ETT?
laryngoscope
Is sevoflurane cheap or expensive?
expensive - use with a vaporiser in circuit set up
Describe endotracheal tubes (ETT):
material
shape
check
MATERIAL: red rubber, PVC or silicone
SHAPE: preformed curve (not silicone), some have a ‘Murphy eye’ which allows flow of anaesthetic if end is occluded, INTERNAL diameter marked in mm.
CHECK: cuff before use.
Indications to use a laryngeal mask
if animal can’t be intubated or ET will get in way of procedure, this still allows O2 delivery. Cat and rabbit types
What are HMEs?
Heat and Moisture Exchangers (sponge inside traps the water vapour –> gases are then warmed)
