Question:medium
The most effective breathing circuit during spontaneous ventilation is:
The most effective breathing circuit during spontaneous ventilation is:
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Think Magill circuit - valve at the patient end conserves fresh gas during spontaneous breathing.
Updated On: Jun 24, 2026
- Mapleson A
- Mapleson B
- Mapleson C
- Mapleson D
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The Correct Option is A
Solution and Explanation
Step 1: The trick with Mapleson systems is to match the geometry of the bag, fresh-gas inlet and pop-off valve to the ventilation mode that wastes the least fresh gas.
Step 2: In the Magill (Mapleson A) layout the relief valve sits near the patient. While a patient breathes on his own, the early expirate (anatomical dead-space, which is fresh) is retained in the tubing and reused, and only the later CO2-rich alveolar gas escapes through the valve. The result is no significant rebreathing at a fresh gas flow about equal to alveolar minute ventilation.
Step 3: Because of this economy, Mapleson A is the circuit of choice for spontaneous ventilation. By contrast, Mapleson D wins for controlled ventilation, while B and C are inefficient and demand high flows in either mode.
\[\boxed{\text{Mapleson A}}\]
Step 2: In the Magill (Mapleson A) layout the relief valve sits near the patient. While a patient breathes on his own, the early expirate (anatomical dead-space, which is fresh) is retained in the tubing and reused, and only the later CO2-rich alveolar gas escapes through the valve. The result is no significant rebreathing at a fresh gas flow about equal to alveolar minute ventilation.
Step 3: Because of this economy, Mapleson A is the circuit of choice for spontaneous ventilation. By contrast, Mapleson D wins for controlled ventilation, while B and C are inefficient and demand high flows in either mode.
\[\boxed{\text{Mapleson A}}\]
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