Anaesthetic circuits Flashcards
What should be considered when choosing an anaesthetic system?
- Patient size
- Type of ventilation
- Cost
- Inhalation agent
- Length of procedure
What are non-rebreathing systems?
- Semi-closed systems
- High fresh gas flows wash-out expired gases to prevent rebreathing; removed via adjustable pressure limiting valve (APL) which must remain open
What is the mapleson classification?
- Used to categorise non-rebreathing circuits based on appearance and whether you can perform IPPV
- Class A = Magill
- Class A = Parallel/Mini lack
- Class D = Bain
- Class E = Ayre’s T piece
- Class F = Jackson Rees Modified
What is a Magill?
- Non-rebreathing system
- Not suitable for IPPV
- 200ml/kg/min
- For patients 5-80 kg
What is a Lack?
- Non-rebreathing system
- Not suitable for IPPV
- 200ml/kg/min
- For patients over 10kg
- Mini lacks can used for patients under 10kg
- Have lower oxygen and volatile agent requirements than T-piece
What is a Co-axial Bain?
- Non-rebreathing system
- Suitable for IPPV
- 200-400ml/kg/min
- For patients 8-70kg
What is the Ayre’s T-piece and Jackson Rees modified?
- Non-rebreathing system
- Suitable for IPPV
- 500-600ml/kg/min
- For patients under 10kg
What do rebreathing systems consist of?
- Exhalation unidirectional valve
- Pop-off valve
- Inhalation unidirectional valve
- Pressure manometer
- Reservoir bag
- CO2 absorbent canister
- Breathing tubes
What is the carbon dioxide absorber canister?
- Incorporate a chemical soda-lime
- Absorbs the CO2 content of expired gases
- Contains calcium hydroxide 90%, sodium hydroxide 5%, silicates 5% and pH indicator
What is a unidirectional valve?
- Controls the direction of gas flow
- Enables anaesthesist observation for proper placement of ET tube and monitor rate and depth of breathing
Flutter valves can become stuck
What is a humphrey ade system with soda lime?
- Rebreathing system
- Ideal for IPPV
- Initially 3 litres/min to fill up system then 10mls/kg/min
- For patients 7-100kg
- Lever should be up
What is the humphrey ade without soda lime?
- Non-rebreathing system
- Ideal for IPPV
- Initially 2 litres/min to fill up system and then 70-100mls/kg/min
- For patients under 7kg
- Lever should be down
What is the circle?
- Rebreathing system
- Ideal for IPPV
- Initially 100mls/kg/min to de-nitonise the system then 10mls/kg/min
- For patients over 10kg
How is IPPV given?
- Close APL valve
- Squeeze bag
- Open valve
What is the reservoir bag?
- Flexible storage reservoir
- Can observe patient respiration and confirm proper ETT placement
- Allows delivery of anaesthetic gases to patient and can perform IPPV
What are the advantages of non-rebreathing systems?
- Reliable concentrations delivered
- Range of sizes available
- Decreased resistance to breathing
- Disposable
What are the disadvantages of non-rebreathing systems?
- Gases are dry and cold
- Increases oxygen use
- The increased cost of volatile agent
- Increased environment pollution
What are the advantages of rebreathing systems?
- Warms and humidifies gases
- Two breathing system sizes
- Decreased use and cost of gases
- Decreased volatile agent use and cost
- Decreased environmental pollution
What are the disadvantages of rebreathing systems?
- Slow changes of volatile agent to patient
- Increases resistance to breathing
- Has many parts
- Requires monitoring of parts and CO2 absorber
What is the fresh gas flow calculation?
- Kg x circuit calculation = answer/1000 litres
- If the circuit calculation is a range, must do both ranges and leave answer as a range
What is capnography?
- When a sample of gas is taken away for monitoring
- When calculating an extra 200 mls/min must be added
