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Dynamic hyperinflation during invasive ventilation for COPD — SCE Respiratory MCQ

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HardCritical CareDynamic hyperinflation during invasive ventilation for COPDSCE Respiratory

A 68-year-old man with severe COPD and chronic hypercapnia is intubated after worsening consciousness despite optimised non-invasive ventilation. His usual serum bicarbonate is 34 mmol/L. He is receiving controlled volume ventilation with a tidal volume of 6 mL/kg predicted body weight, respiratory rate 24 breaths/min and external PEEP 8 cmH2O. Shortly after intubation, his blood pressure falls to 76/42 mmHg. Peak airway pressure is 48 cmH2O, plateau pressure is 27 cmH2O, and the expiratory flow trace has not returned to zero when the next breath begins. Disconnecting the ventilator circuit produces a rapid but transient improvement in blood pressure. Lung ultrasound shows bilateral lung sliding and the tracheal tube is patent. Arterial blood gas analysis shows pH 7.23 and PaCO2 11.0 kPa. Which ventilator strategy is most appropriate?

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

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Correct answer: C — Reduce the respiratory rate to 12 breaths/min, shorten inspiratory time and target an I:E ratio of at least 1:3

Explanation lettering: E = shown as A · A = shown as B · B = shown as C · C = shown as E

The large peak-to-plateau pressure gradient indicates increased airway resistance rather than excessive static alveolar pressure. Failure of expiratory flow to return to zero, haemodynamic improvement during circuit disconnection and severe airflow obstruction together identify dynamic hyperinflation with intrinsic PEEP. Raised intrathoracic pressure is impairing venous return and causing hypotension. The priority is therefore to reduce minute ventilation and increase expiratory time. BTS/ICS guidance recommends a low respiratory frequency of 10–15 breaths/min and an I:E ratio of at least 1:3 during controlled ventilation in obstructive disease. Shortening inspiratory time, usually by increasing inspiratory flow, further extends expiration. Permissive hypercapnia targeting pH 7.20–7.25 may be necessary; normalising PaCO2 is especially inappropriate in a chronically hypercapnic patient. A and D increase delivered minute ventilation and shorten effective expiratory time, worsening gas trapping. C is attractive because external PEEP can reduce triggering effort during assisted ventilation, but it does not abolish intrinsic PEEP and 14 cmH2O exceeds the BTS/ICS usual ceiling of 12 cmH2O. E is premature: controlled ventilation may need to continue while airway resistance remains severe, because spontaneous effort and asynchrony can aggravate breath stacking.

Reference: BTS/ICS guideline for the ventilatory management of acute hypercapnic respiratory failure in adults (March 2016; correction June 2017) — https://thorax.bmj.com/content/71/Suppl_2/ii1 BTS/ICS Guideline for the Ventilatory Management of Acute Hypercapnic Respiratory Failure in Adults (Guideline published March 2016; webpage checked 18 August 2026) — https://www.brit-thoracic.org.uk/clinical-resources/guidelines/niv/