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Reduced FRC under anaesthesia — FRCA Primary MCQ

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ModeratePhysiologyReduced FRC under anaesthesiaFRCA Primary

After induction in an obese patient, airway pressure rises and oxygen saturation falls during supine ventilation. Which change caused by general anaesthesia is most relevant?

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Correct answer: B — Reduced functional residual capacity

General anaesthesia and the supine position reduce functional residual capacity, promoting airway closure and atelectasis, especially in obesity. Chest wall compliance usually falls rather than rises in this setting. Oxygen consumption may fall under anaesthesia but this does not explain rapid desaturation. Recruitment, PEEP and positioning address the underlying mechanics.

Reference: West Respiratory Physiology; Nunn's Applied Respiratory Physiology