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One-Lung Ventilation Hypoxia — FRCA Final MCQ

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HardCardiothoracic AnaesthesiaOne-Lung Ventilation HypoxiaFRCA Final

A 68-year-old man with COPD (ASA III) is undergoing right pneumonectomy. One-lung ventilation is established through a left-sided double-lumen tube. His SpO2 falls to 88% despite an FIO2 of 1.0. Fibreoptic bronchoscopy confirms correct tube position, peak airway pressure and delivered tidal volume are unchanged, and 5 cmH2O PEEP is already applied to the ventilated left lung. The right pulmonary artery has been dissected and is accessible. Which intervention is most likely to produce the greatest immediate improvement in oxygenation?

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

Reveal the answer and explanation

Correct answer: A — Ask the surgeon to clamp the pulmonary artery on the operative side

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

E is correct. With FIO2 1.0, confirmed tube position, unchanged airway pressures and PEEP already applied, the residual cause of desaturation is right-to-left shunt through the perfused, collapsed right lung. Because the right pulmonary artery is already exposed and will be divided as part of pneumonectomy, clamping it abolishes that shunt and produces the largest, fastest rise in SpO2. A is the standard rescue when the shunt cannot be removed, but CPAP only oxygenates part of the shunted blood, re-inflates the operative lung and obstructs the surgical field. B risks overdistending the dependent lung, raising its pulmonary vascular resistance and diverting flow back to the non-ventilated lung. C corrects carbon dioxide, not shunt. D abandons protective ventilation and similarly worsens dependent-lung vascular resistance without correcting shunt.

Reference: Hypoxaemia during one lung ventilation (peer-reviewed UK anaesthetic educational review), 2023. https://pubmed.ncbi.nlm.nih.gov/37600211/