Respiratory alkalosis — FRCA Primary MCQ

Correct answer: A — Raised PaCO2 lowers alveolar oxygen tension

The abnormality is excessive ventilation causing low PaCO2 rather than a metabolic process. Perfusion of non-ventilated alveoli creates shunt is less appropriate because it would fit a different clinical clue or a separate anaesthetic problem. Reduced baroreceptor firing increases sympathetic outflow is less appropriate because it would fit a different clinical clue or a separate anaesthetic problem. ADH inserts aquaporin-2 channels in collecting ducts 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