Altitude Immediate Hyperventilation — FRCA Primary MCQ
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Correct answer: C — Hypoxaemia-driven hyperventilation through peripheral chemoreceptor stimulation
The best answer is “Hypoxaemia-driven hyperventilation through peripheral chemoreceptor stimulation”. Reduced inspired oxygen pressure lowers arterial oxygen tension and promptly stimulates the carotid bodies, increasing ventilation. The initial respiratory alkalosis is compensated later by renal bicarbonate excretion. Increased 2,3-BPG and erythropoiesis develop over longer time courses, so they cannot be the first response to abrupt exposure.
Reference: Royal College of Anaesthetists, Primary FRCA Syllabus 2021: https://www.rcoa.ac.uk/sites/default/files/documents/2026-01/Primary-FRCA-Syllabus.pdf