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COPD with ventilator-induced dynamic hyperinflation and haemodynamic compromise — SCE Respiratory MCQ

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HardMechanical VentilationCOPD with ventilator-induced dynamic hyperinflation and haemodynamic compromiseSCE Respiratory

A 67-year-old man with severe COPD is invasively ventilated for an infective exacerbation after non-invasive ventilation fails. He is deeply sedated, pharmacologically paralysed and receiving volume-controlled ventilation. Predicted body weight is 70 kg. Current settings are tidal volume 490 mL, respiratory rate 24 breaths/min, inspiratory flow 45 L/min, PEEP 5 cmH2O and FiO2 0.35. His blood pressure falls to 76/42 mmHg. Peak inspiratory pressure is 52 cmH2O, but plateau pressure is 24 cmH2O. The expiratory flow waveform has not returned to zero before each subsequent breath. An end-expiratory hold measures total PEEP at 18 cmH2O. Arterial blood gases show pH 7.23, PaCO2 9.2 kPa and PaO2 9.6 kPa. Bilateral lung sliding is present on ultrasonography. When the ventilator circuit is briefly disconnected during assessment, prolonged expiration occurs and his blood pressure rapidly improves. Which ventilator strategy is most appropriate when ventilation is resumed?

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Correct answer: B — Volume control with tidal volume 420 mL, respiratory rate 12 breaths/min, inspiratory flow 80 L/min and PEEP 5 cmH2O

Explanation lettering: D = shown as A · E = shown as D · A = shown as E

The non-zero end-expiratory flow, intrinsic PEEP of 13 cmH2O, marked peak–plateau pressure difference and rapid haemodynamic improvement during circuit disconnection identify severe expiratory flow limitation with dynamic hyperinflation. Raised intrathoracic pressure is impairing venous return and causing obstructive shock. Management must reduce minute ventilation and extend expiratory time: a low respiratory rate, modest tidal volume and high inspiratory flow produce a short inspiration and prolonged expiration. Hypercapnia should be accepted, with a pragmatic pH target around 7.20–7.25, rather than pursuing normocapnia at the cost of further gas trapping. A uses a lung-protective tidal volume but the high respiratory rate perpetuates incomplete expiration. C lowers respiratory rate but the 10 mL/kg tidal volume increases end-inspiratory lung volume and may preserve hyperinflation. D may initially attract candidates because external PEEP can reduce trigger work in spontaneously breathing patients with intrinsic PEEP; this patient is passive and haemodynamically compromised, and PEEP 14 cmH2O may worsen hyperinflation. E provides insufficient expiratory time because its long inspiratory time occupies a substantial proportion of each respiratory cycle. Controlled ventilation should continue until airway resistance falls; spontaneous modes can then be reintroduced.

Reference: BTS/ICS Guideline for the Ventilatory Management of Acute Hypercapnic Respiratory Failure in Adults (March 2016) — https://www.brit-thoracic.org.uk/clinical-resources/guidelines/niv/ Management of Asthma and COPD Exacerbations in Adults in the ICU (March 2025) — https://pubmed.ncbi.nlm.nih.gov/40330435/