2016A Question 02
Draw and label a circle breathing system. Explain its advantages and disadvantages.
89% of candidates achieved a pass in this question
Main Points expected for a pass:
- A legible and accurate diagram of a circle breathing system.
- Correct components in the correct order.
- A reasonable list of advantages and disadvantages. Additional points could be gained for:
- Further detail on how components were arranged.
- This question was generally well handled.
- Some candidates spent too much time on one half of the question.
- There was confusion regarding the location of the APL valve.
- Illegible handwriting
- Poor layout and structure and evidence of poor time management
- The main reason for failing this question was insufficient core knowledge
Circle system is a semi-closed, re-breathing anaesthetic circuit.
- Volatile anaesthetic: Accurate, minimal waste
- O2: Accurate, can deliver 100%
- CO2: Efficient removal by:
- Scavenger (earlier in expiratory limb – to spare CO2 absorber))
- CO2 absorber (later in expiratory limb)
- Minimal dead space: Only tubing distal to Y piece and HME
- Low resistance
- Humidification and warming by CO2 absorber
- Sodalime remote from airway hence minimal dust inhalation
- ↓ Waste
- ↓ O2 pollution
- Equilibration between FGF and circuit-patient gas composition is dependent on FGF rate
- FiO2 can fall below 0.21 if low fresh gas flow rate and low fresh gas PO2 (since semi-closed)
- Sodalime degradation products: CO, Compound A
- Higher resistance than Mapleson E and F due to valves and longer tubing
- Possibility of injury if dysfunctional valves, scavenging system
- Atmospheric pollution from scavenging