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Neonatal functional residual capacity — MRCPCH TAS MCQ

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HardPhysiologyNeonatal functional residual capacityMRCPCH TAS

A 2-week-old infant with mild viral coryza desaturates during feeding. Examination shows nasal obstruction and mild recession; chest radiograph is clear. Which physiological feature most increases vulnerability to hypoxaemia?

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

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Correct answer: C — Low functional residual capacity with high oxygen consumption

Infants have high oxygen consumption and limited functional residual capacity, so oxygen saturation can fall quickly during obstruction or apnoea. Mature collateral ventilation is not a protective feature of early infancy. The pearl is that feeding and nasal obstruction can unmask limited respiratory reserve in young infants.

Reference: Ganong's Review of Medical Physiology; Nelson Textbook of Pediatrics; RCPCH Theory examination syllabi