West zone 1 — FRCA Primary MCQ
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Correct answer: C — Ventilation of poorly perfused alveoli increases dead space
When alveolar pressure exceeds pulmonary arterial pressure, alveolar dead space increases. Raised PaCO2 lowers alveolar oxygen tension is less appropriate because it would fit a different clinical clue or a separate anaesthetic problem. Hypoxic pulmonary vasoconstriction diverts blood flow is less appropriate because it would fit a different clinical clue or a separate anaesthetic problem. Closing capacity exceeding FRC causes airway closure is less appropriate because it would fit a different clinical clue or a separate anaesthetic problem. Acidosis shifts the oxyhaemoglobin curve right is less appropriate because it would fit a different clinical clue or a separate anaesthetic problem. In Primary FRCA physiology, the correct answer is usually the variable that best explains the observed change in the anaesthetised patient.
Reference: West's Respiratory Physiology; Ganong Review of Medical Physiology; Primary FRCA textbooks