2016A Question 02
Draw and label a circle breathing system. Explain its advantages and disadvantages.
Examiner Report
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.
Common problems:
- 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
Model Answer
Structure:
- Define
- Diagram
- Pros
- Cons
Define
Circle system is a semi-closed, re-breathing anaesthetic circuit.
Diagram
Pros
| Factor | Description |
|---|---|
| Main features | - 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) |
| Secondary features | - Minimal dead space: Only tubing distal to Y piece and HME - Low resistance - Humidification and warming by CO2 absorber |
| Logistics | - Sodalime remote from airway hence minimal dust inhalation - ↓ Waste - ↓ O2 pollution |
Cons
| Factor | Description |
|---|---|
| Main features | - 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 |
| Secondary features | - Higher resistance than Mapleson E and F due to valves and longer tubing - Possibility of injury if dysfunctional valves, scavenging system |
| Logistics | - Expensive - Complicated - Bulky - Atmospheric pollution from scavenging |