During one-lung ventilation (OLV) for left pneumonectomy, hypoxaemia occurs. Which mechanism primarily contributes to hypoxaemia during OLV?

• A Reduced cardiac output causing increased oxygen extraction from ventilated lung
• B Hyperventilation of the ventilated lung causing respiratory alkalosis and left shift of O2-Hb curve
• C Intrapulmonary shunt from continued perfusion of the non-ventilated (collapsed) lung ✓
• D Endobronchial tube cuff herniating into the carina obstructing ventilated lung

Explanation

During OLV, the non-ventilated (operative) lung receives approximately 30–40% of pulmonary blood flow (without ventilation), creating a pure intrapulmonary shunt — blood passes through unventilated alveoli and returns to the systemic circulation desaturated. Hypoxic pulmonary vasoconstriction (HPV) in the collapsed lung reduces this shunt to approximately 20–30% by redirecting blood to the ventilated lung, but HPV is impaired by volatile anaesthetics and vasodilators. Management includes FiO2 1.0, optimising PEEP to ventilated lung, continuous positive airway pressure (CPAP 5–10 cmH2O) to the non-ventilated lung, and ensuring appropriate DLT/bronchial blocker position.

Reference: Morgan & Mikhail's Clinical Anesthesiology, 6th ed.

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Written and medically reviewed by the StethoPrep medical team.