The Mapleson classification of breathing systems is based on a functional principle. In which Mapleson system is CO2 rebreathing LEAST likely during controlled ventilation at moderate fresh gas flows?

• A Mapleson A (Magill)
• B Mapleson E (Ayre's T-piece)
• C Mapleson D (Bain) ✓
• D Mapleson C (Waters)

Explanation

The Mapleson D and its coaxial variant (Bain) are most efficient for controlled ventilation because the fresh gas inlet is near the patient, expiration travels away from the patient along the reservoir tube and exits via the APL valve. During controlled ventilation, a fresh gas flow of 70–100 mL/kg/min is sufficient to prevent rebreathing. Mapleson A (Magill) is highly efficient for spontaneous breathing (FGF = alveolar ventilation ~70 mL/kg/min) but very wasteful during controlled ventilation, requiring FGF 2–3× minute ventilation. Mapleson E/T-piece is efficient for spontaneous breathing in children but not for controlled ventilation.

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

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Written and medically reviewed by the StethoPrep medical team.