Alveolar gas equation — FRCA Primary MCQ

Correct answer: B — Raised PaCO2 lowers alveolar oxygen tension

The alveolar gas equation links increased PaCO2 with reduced PAO2. Hypoxic pulmonary vasoconstriction diverts blood flow is less appropriate because it would fit a different clinical clue or a separate anaesthetic problem. Increased preload increases stroke volume through fibre stretch is less appropriate because it would fit a different clinical clue or a separate anaesthetic problem. Aldosterone increases sodium reabsorption and potassium secretion 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