skip to main content

Dynamic hyperinflation in severe asthma ventilation — FRCA Primary MCQ

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

HardPhysiologyDynamic hyperinflation in severe asthma ventilationFRCA Primary

A patient with severe asthma is ventilated with a high respiratory rate and an I:E ratio close to 1:1. The expiratory flow trace does not return to baseline before the next breath and blood pressure falls. Which ventilator change best addresses the underlying physiology?

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

Reveal the answer and explanation

Correct answer: C — Increase inspiratory time to improve gas mixing

The flow trace indicates incomplete expiration with dynamic hyperinflation, so increasing expiratory time reduces gas trapping and intrathoracic pressure. Raising respiratory rate or tidal volume usually worsens air trapping. The hypotension is caused by impaired venous return from raised intrathoracic pressure. The teaching point is that permissive hypercapnia may be safer than aggressive minute ventilation in severe airflow obstruction.

Reference: RCoA Primary FRCA Syllabus 2026; Ganong's Review of Medical Physiology; West's Respiratory Physiology