FRC Decrease at Induction — FRCA Final MCQ

Instant feedback + full explanation. One question, done properly.

ModerateGeneral AnaesthesiaFRC Decrease at InductionFRCA Final

A 58-year-old man with a body mass index of 45 is scheduled for bariatric surgery. Pre-operative pulmonary function tests show a reduced FRC. At what point during induction of anaesthesia does the FRC decrease most significantly?

Educational content. Not a substitute for clinical judgement or local policy.

Reveal the answer and explanation

Correct answer: D — During induction and loss of consciousness (loss of diaphragmatic tone)

FRC decreases by approximately 15-20% upon induction of anaesthesia and loss of consciousness, primarily due to: loss of inspiratory muscle tone (diaphragm relaxes and moves cephalad), increased intra-abdominal pressure pushing the diaphragm further upward, and loss of chest wall outward recoil. In obese patients, the baseline FRC is already reduced (FRC decreases exponentially with increasing BMI). This reduction may bring FRC below closing capacity, causing airway closure, atelectasis, and intrapulmonary shunting. The decrease occurs before neuromuscular blockade is even administered.

Reference: Lumb AB – 2022 – Nunn's Applied Respiratory Physiology; RCOA – 2023 – Obesity anaesthesia