2016A02 Draw and label a circle breathing system. Explain its advantages and disadvantages.



·      Define

·      Diagramme

·      Pros

·      Cons



Circle system is a semi-closed, re-breathing anaesthetic circuit.




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Main features

·  Volatile anaesthetic: accurate, minimal waste

·  O2: accurate, can deliver 100%

·  CO2: efficient removal by

o Scavenger (earlier in expiratory limb – to spare CO2 absorber))

o 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


·  Sodalime remote from airway hence minimal dust inhalation

·  ↓Waste

·  ↓O2 pollution



Main features

·  Change in vapour dial slow to equilibrate with circuit and patient

·  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


·  Expensive

·  Complicated

·  Bulky

·  Atmospheric pollution from scavenging




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