Which of the following is the most common cause of hypoxia during general anesthesia in the immediate postinduction period?

Explanation

## Most Common Cause of Hypoxia in Immediate Postinduction Period **Key Point:** Airway obstruction or malposition of the endotracheal tube (ETT) is the most common cause of hypoxia in the immediate postinduction period, accounting for the majority of preventable hypoxic episodes. ### Mechanism During induction and intubation: - Tube may be positioned in the right mainstem bronchus (most common malposition) - Tube may be advanced too far into the pharynx or esophagus - Secretions, blood, or edema may obstruct the tube - Tube kinking or biting (if not protected) ### Differential Diagnosis of Hypoxia Causes | Cause | Timing | Mechanism | Prevention | |-------|--------|-----------|------------| | **Airway obstruction/malposition** | Immediate postinduction | Tube in wrong position or blocked | Auscultate both lung fields, check tube position on CXR | | Hypoventilation | Early-to-mid procedure | Inadequate minute ventilation | Monitor ETCO₂, adjust ventilator settings | | Diffusion hypoxia | Recovery phase | Rapid N₂O washout dilutes alveolar O₂ | Use high FiO₂ at end of anesthesia | | Intracardiac shunt | Chronic/congenital | Right-to-left shunting | Preoperative assessment | | Atelectasis | Intraoperative | Airway closure in dependent zones | Use PEEP, recruitment maneuvers | **High-Yield:** The first action when hypoxia is detected postinduction is to **check tube position** — auscultate both lung fields symmetrically and confirm bilateral breath sounds. **Clinical Pearl:** Right mainstem intubation is the most frequent malposition because the right mainstem is more vertical and in line with the trachea. Always withdraw the tube 1–2 cm if right-sided breath sounds are louder. ### Why Other Causes Are Less Common Immediately Postinduction - **Diffusion hypoxia:** Occurs during recovery/emergence when N₂O is rapidly eliminated - **Residual neuromuscular blockade:** Would cause hypoventilation, but hypoxia develops more gradually - **Intracardiac shunt:** A chronic anatomical defect; would present preoperatively, not acutely postinduction