The Mapleson A (Magill's) breathing system is MOST efficient for spontaneous ventilation. What is the minimum fresh gas flow (FGF) required for spontaneous ventilation to prevent rebreathing in Mapleson A?

• A 0.5 × minute ventilation
• B 2× minute ventilation
• C 3× minute ventilation
• D Equal to alveolar minute ventilation (approximately 70 mL/kg/min or 1× minute ventilation) ✓

Explanation

The Mapleson A (Magill) circuit is the most efficient for spontaneous ventilation: alveolar gas (high CO2) is first to be expired and preferentially exits through the APL valve (which opens at end-expiration), while fresh gas (CO2-free) fills the dead-space and reservoir bag. A FGF equal to alveolar minute ventilation (approximately 0.7× minute ventilation or ~70 mL/kg/min) prevents rebreathing. For controlled ventilation, the Mapleson A is the LEAST efficient, requiring FGF of 3× minute ventilation. The Mapleson D/Bain circuit is opposite — most efficient for controlled ventilation (FGF 70–100 mL/kg/min) but less efficient for spontaneous (FGF 150–200 mL/kg/min).

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.