The Mapleson A (Magill) system is MOST efficient for which clinical scenario?

• A Controlled ventilation in adults requiring high fresh gas flow
• B Paediatric spontaneous breathing patients
• C Controlled ventilation in neonates
• D Spontaneous breathing in adults — fresh gas flow of approximately 70% of minute ventilation (1 × MV) prevents rebreathing ✓

Explanation

The Mapleson A (Magill) circuit is highly efficient for spontaneous breathing in adults: a fresh gas flow equal to approximately 70–100% of minute ventilation (alveolar ventilation ~70% of MV) prevents rebreathing of CO₂ because alveolar gas (high CO₂) is exhaled first into the expiratory limb and reservoir bag, while fresh gas occupies the dead space near the patient — the CO₂-rich gas is vented through the expiratory valve before rebreathing. However, it is INEFFICIENT for controlled ventilation (requires flows 2–3× MV). The Mapleson D (Bain modification) is preferred for controlled ventilation. Mapleson E/F (Ayre's T-piece) is used in paediatrics.

Reference: Morgan & Mikhail's Clinical Anesthesiology, 6th ed.

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Written and medically reviewed by the StethoPrep medical team.