CO2 carriage — FRCA Primary MCQ

Correct answer: E — Raised PaCO2 lowers alveolar oxygen tension

Most carbon dioxide is transported as bicarbonate. The loop of Henle creates the medullary osmotic gradient 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. Pain and temperature ascend in the spinothalamic tract 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. 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