Anaesthesia breathing circuits

Question 1

Function of breathing systems

Answer 1

• Removal of CO2
• Supply O2 to patient
• Supply anaesthetic gases to patient
• Allow for intermittent positive pressure ventilation (IPPV)

Question 2

Anaesthetic breathing circuits

Answer 2

• Anaesthetic breathing circuits are described as either rebreathing or non-rebreathing
• In rebreathing circuits there will be CO2 absorbent present
• In non-rebreathing circuits the CO2 is flushed out by the continuous flow of fresh gas

Question 3

Types of rebreathing circuits

Answer 3

• Circle
• To and fro
• Humphrey ADE - circle system

Question 4

Types of non-rebreathing circuits

Answer 4

• Ayer’s modified t-piece
• Bain
• Lack
• Magill
• Humphrey ADE

Question 5

Rebreathing advantages

Answer 5

• Require low gas flow rates, reducing cost in relation to delivery of anaesthetic agent delivery
• Reduced environmental contamination with waste gas
• Reduced heat loss from patient - gases require less warning from the patient than in non-rebreathing circuits

Question 6

Rebreathing disadvantages

Answer 6

• Altering the level of volatile agent within the circuit takes a while to change
• Depending on the gas flow rate and volume of the circuit, CO2 absorbent and valves create resistance
• Require maintenance associated with CO2 absorbent that needs regular changing
• Can be expensive to purchase
• Require an understanding of how the circuit works

Question 7

Non-rebreathing advantages

Answer 7

• Concentration of the volatile agent can be altered quickly
• Minimal circuit resistance
• Cheap to purchase
• Easy to use

Question 8

Non-rebreathing disadvantages

Answer 8

• High gas flow rate increases costs associated with gases and inhalant agents
• Increased environment contamination
• Potential for rebreathing if patient breathes too rapidly - to counteract this gas flow rate must be increased
• Significant heat loss through respiratory tract due to warming of inspired gas

Question 9

Circle system advantages

Answer 9

• Low fresh gas flow requirements, reducing medical gases costs
• Decreased use of volatile agents
• Less environmental contamination
• Reduced heat loss from patient
• Ideal for IPPV
• Inspired gases are moistened as they pass through the soda lime because the reaction within the CO2 absorbent produces water

Question 10

Circle system disadvantages

Answer 10

• The canister needs to be filled with CO2 absorbent as per manufacturers guidelines
• Some canisters are difficult to fill
• The canisters are difficult to clean
• Canisters are often a source of gas leaks
• Maintenance takes time and skill
• CO2 absorbent needs to be changed regularly which is expensive
• Unsuitable for patients that are hyperthermic

Question 11

Soda lime

Answer 11

• Different makes of soda lime have different colour changes from fresh soda lime to exhausted soda lime
• White to purple or pink to white, the manufacturers instructions will indicate the expected colour change