The Mapleson A (Magill) system is considered the most efficient breathing system for spontaneous ventilation. The minimum fresh gas flow (FGF) required to prevent CO2 rebreathing during spontaneous ventilation with a Mapleson A system is:

• A Equal to alveolar ventilation only (approximately 60 mL/kg/min)
• B 2–3 times the minute ventilation to ensure adequate washout
• C Equal to minute ventilation (approximately 70–100 mL/kg/min) ✓
• D Equal to tidal volume multiplied by 5

Explanation

The Mapleson A (Magill) system is highly efficient for spontaneous ventilation because the APL (expiratory) valve is positioned near the patient and the reservoir bag is distal. During exhalation, dead-space gas (CO2-free) enters the corrugated tubing first, and alveolar gas is vented through the APL valve. During inspiration, fresh gas and dead-space gas are inhaled. The FGF needed equals approximately the alveolar minute ventilation (about 70 mL/kg/min or minute ventilation); some texts cite FGF equal to minute ventilation as the practical threshold. For controlled ventilation, the Mapleson A system is the least efficient, requiring FGF 2–3 times minute ventilation.

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

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Written and medically reviewed by the StethoPrep medical team.