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Mapleson A rebreathing — FRCA Primary MCQ

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HardPhysics and Clinical MeasurementMapleson A rebreathingFRCA Primary

A patient breathing spontaneously through a Mapleson A system during maintenance anaesthesia has a fresh gas flow well below minute ventilation. Inspired CO2 begins to rise. Which change most effectively reduces rebreathing?

Educational content. Not a substitute for clinical judgement or local policy.

Reveal the answer and explanation

Correct answer: E — Increase fresh gas flow

In a Mapleson A system during spontaneous ventilation, adequate fresh gas flow prevents rebreathing by flushing alveolar gas from the system. Closing the expiratory valve increases resistance and risks rebreathing. Increasing apparatus dead space worsens CO2 rebreathing. The key point is that breathing system performance depends on patient ventilation mode and fresh gas flow.

Reference: RCoA Primary FRCA Syllabus 2026; Davis and Kenny Basic Physics and Measurement in Anaesthesia