The Mapleson D breathing system (Bain circuit) is considered more efficient for controlled ventilation than spontaneous breathing. What minimum fresh gas flow (FGF) is required for controlled ventilation in an adult to prevent rebreathing?

• A Equal to alveolar ventilation (approximately 60 mL/kg/min)
• B Equal to minute ventilation (70 mL/kg/min)
• C 2–3 times minute ventilation (approximately 70 mL/kg/min) ✓
• D Only 1 L/min with carbon dioxide absorbers

Explanation

The Mapleson D/Bain circuit has the expiratory limb opening at the patient end and the FGF entering at the machine end. For spontaneous ventilation, FGF must be 2–3 times minute ventilation (~200–300 mL/kg/min) to prevent CO2 rebreathing. For controlled ventilation, where expiration is directed toward the APL valve, FGF of approximately 70–100 mL/kg/min (roughly once the minute ventilation) is sufficient to flush the corrugated tubing before the next breath. The Bain circuit is thus classified as the most efficient Mapleson system for IPPV.

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

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Written and medically reviewed by the StethoPrep medical team.