Cerebral CO2 response — FRCA Primary MCQ

Correct answer: B — Hypocapnia causes cerebral vasoconstriction

Low PaCO2 causes cerebral vasoconstriction and reduces cerebral blood volume. Increased preload increases stroke volume through fibre stretch is less appropriate because it would fit a different clinical clue or a separate anaesthetic problem. Small myelinated fibres block relatively early 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. Hypoxic pulmonary vasoconstriction diverts blood flow 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