Anaesthetic circuits

Question 1

What should be considered when choosing an anaesthetic system?

Answer 1

• Patient size
• Type of ventilation
• Cost
• Inhalation agent
• Length of procedure

Question 2

What are non-rebreathing systems?

Answer 2

• 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

Question 3

What is the mapleson classification?

Answer 3

• 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

Question 4

What is a Magill?

Answer 4

• Non-rebreathing system
• Not suitable for IPPV
• 200ml/kg/min
• For patients 5-80 kg

Question 5

What is a Lack?

Answer 5

• 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

Question 6

What is a Co-axial Bain?

Answer 6

• Non-rebreathing system
• Suitable for IPPV
• 200-400ml/kg/min
• For patients 8-70kg

Question 7

What is the Ayre’s T-piece and Jackson Rees modified?

Answer 7

• Non-rebreathing system
• Suitable for IPPV
• 500-600ml/kg/min
• For patients under 10kg

Question 8

What do rebreathing systems consist of?

Answer 8

• Exhalation unidirectional valve
• Pop-off valve
• Inhalation unidirectional valve
• Pressure manometer
• Reservoir bag
• CO2 absorbent canister
• Breathing tubes

Question 9

What is the carbon dioxide absorber canister?

Answer 9

• Incorporate a chemical soda-lime
• Absorbs the CO2 content of expired gases
• Contains calcium hydroxide 90%, sodium hydroxide 5%, silicates 5% and pH indicator

Question 10

What is a unidirectional valve?

Answer 10

• 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

Question 11

What is a humphrey ade system with soda lime?

Answer 11

• 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

Question 12

What is the humphrey ade without soda lime?

Answer 12

• 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

Question 13

What is the circle?

Answer 13

• Rebreathing system
• Ideal for IPPV
• Initially 100mls/kg/min to de-nitonise the system then 10mls/kg/min
• For patients over 10kg

Question 14

How is IPPV given?

Answer 14

• Close APL valve
• Squeeze bag
• Open valve

Question 15

What is the reservoir bag?

Answer 15

• Flexible storage reservoir
• Can observe patient respiration and confirm proper ETT placement
• Allows delivery of anaesthetic gases to patient and can perform IPPV

Question 16

What are the advantages of non-rebreathing systems?

Answer 16

• Reliable concentrations delivered
• Range of sizes available
• Decreased resistance to breathing
• Disposable

Question 17

What are the disadvantages of non-rebreathing systems?

Answer 17

• Gases are dry and cold
• Increases oxygen use
• The increased cost of volatile agent
• Increased environment pollution

Question 18

What are the advantages of rebreathing systems?

Answer 18

• Warms and humidifies gases
• Two breathing system sizes
• Decreased use and cost of gases
• Decreased volatile agent use and cost
• Decreased environmental pollution

Question 19

What are the disadvantages of rebreathing systems?

Answer 19

• Slow changes of volatile agent to patient
• Increases resistance to breathing
• Has many parts
• Requires monitoring of parts and CO2 absorber

Question 20

What is the fresh gas flow calculation?

Answer 20

• Kg x circuit calculation = answer/1000 litres
• If the circuit calculation is a range, must do both ranges and leave answer as a range

Question 21

What is capnography?

Answer 21

• When a sample of gas is taken away for monitoring
• When calculating an extra 200 mls/min must be added