Regarding Mapleson breathing circuits used with spontaneously breathing anaesthetised patients, which statement is correct?

• A Mapleson C requires the lowest fresh gas flow in all modes
• B Mapleson D is the most efficient circuit for spontaneous ventilation
• C All Mapleson circuits have equal efficiency regardless of mode of ventilation
• D Mapleson A is the most efficient circuit for spontaneous ventilation ✓

Explanation

Mapleson D (Magill circuit) is the most efficient for spontaneous ventilation because exhaled gas exits preferentially through the spill valve near the patient end before fresh gas reaches it, allowing safe use at fresh gas flows near minute ventilation. For controlled ventilation the situation reverses and Mapleson A becomes the more efficient circuit. This reversal is the classic discriminating fact examined on Mapleson systems.

Reference: Miller's Anesthesia, 9th ed.

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Written and medically reviewed by the StethoPrep medical team.