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Respiratory compensation for metabolic acidosis — FRCA Primary MCQ

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ModeratePhysiologyRespiratory compensation for metabolic acidosisFRCA Primary

A patient with chronic renal failure has metabolic acidosis. Despite low bicarbonate, minute ventilation is increased and PaCO2 is 3.6 kPa. Which compensatory mechanism is most likely?

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

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Correct answer: D — Reduced central chemoreceptor response to hydrogen ions

Metabolic acidosis stimulates ventilation, lowering PaCO2 as respiratory compensation. In chronic renal failure, renal ammonium excretion is impaired rather than increased. The lungs cannot excrete bicarbonate directly but can alter CO2. The pearl is that compensation moves pH towards normal but does not overcorrect the primary disorder.

Reference: RCoA Primary FRCA Syllabus 2026; Ganong's Review of Medical Physiology; West's Respiratory Physiology