Surfactant deficiency — FRCA Primary MCQ

Correct answer: B — Closing capacity exceeding FRC causes airway closure

Surfactant reduces surface tension and stabilises small alveoli. Citrate binds ionised calcium 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. Chronic hypertension shifts cerebral autoregulation right 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. 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