## Most Common Cause of Intraoperative Hypoxia **Key Point:** Endobronchial intubation is the single most common preventable cause of intraoperative hypoxia, accounting for 20–30% of cases. It occurs when the endotracheal tube advances too far into the right mainstem bronchus, occluding the left bronchus and causing left lung collapse. ### Clinical Presentation - Sudden drop in SpO₂ despite adequate FiO₂ and ventilation - Unequal breath sounds (absent on left side) - Decreased compliance, increased airway pressure - Hypotension secondary to hypoxia-induced sympathetic activation followed by myocardial depression ### Mechanism 1. Right mainstem bronchus is more vertical (25° angle) than left (45° angle) 2. During head flexion or patient repositioning, tube migrates distally 3. Left lung becomes atelectatic → shunting → hypoxia ### Diagnosis & Management - **Immediate:** Auscultate bilateral breath sounds; check tube position on chest X-ray - **Treatment:** Withdraw tube 1–2 cm until bilateral breath sounds return; recheck with CXR - **Prevention:** Secure tube at 21–23 cm at teeth for adults; verify position after positioning changes **High-Yield:** This is the **most testable** cause in NEET PG because it is: - Common (happens in ~1 in 10 intubations if not vigilant) - Preventable (proper tube fixation and auscultation) - Rapidly reversible (simple withdrawal of tube) ### Why Other Options Are Less Common in This Scenario - **Tension pneumothorax:** Rare in laparoscopy with proper trocar technique; would present with unilateral absent breath sounds and JVD - **Anaphylaxis:** Would show urticaria, bronchospasm, angioedema; hypotension precedes hypoxia - **Acute coronary syndrome:** Possible but less common as primary cause of acute hypoxia; would show ECG changes [cite:Miller's Anesthesia 8e Ch 29]
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