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OLV Hypoxia in Emphysema — FRCA Final MCQ

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HardCardiothoracic AnaesthesiaOLV Hypoxia in EmphysemaFRCA Final

A 60-year-old man (ASA III) with severe emphysema (FEV1 28% predicted) requires drainage of a large lung abscess. A double-lumen tube is placed for lung isolation. During one-lung ventilation of the non-affected lung, his SpO2 drops to 85% on FiO2 1.0 and PEEP 10. What specific pulmonary physiological factor in emphysema worsens hypoxia during OLV?

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Correct answer: B — Reduced hypoxic pulmonary vasoconstriction due to chronic hypoxia and vascular remodelling

In emphysema, the pulmonary vasculature is chronically remodelled with destruction of the capillary bed and chronic hypoxic vasoconstriction. During OLV, the normal protective mechanism of hypoxic pulmonary vasoconstriction (HPV) in the non-ventilated lung is impaired because: (1) there is less functional vasculature to vasoconstrict, (2) chronic remodelling reduces vasoreactivity, and (3) the ventilated lung has reduced compliance and gas exchange surface area. This means more blood continues to flow through the non-ventilated lung (increased shunt), worsening hypoxia.

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