Life-Threatening Acute Hypoxemic Respiratory Failure Caused by Complete Left Lung Collapse Secondary to Mucus Plug Obstruction in a Toddler: A Case Report.

Acute hypoxemic respiratory failure in toddlers is most commonly associated with severe pneumonia, bronchiolitis, or foreign body aspiration. Complete obstruction of a main bronchus by mucus plugs is an uncommon but potentially life-threatening cause of unilateral lung collapse and severe hypoxemia. We report the case of a previously healthy 17-month-old boy who presented with severe respiratory distress after 3 days of fever and cough. Physical examination revealed marked respiratory distress with absent breath sounds over the left hemithorax. Chest radiography and computed tomography demonstrated complete left lung collapse without evidence of pleural effusion or foreign body. Due to rapidly worsening hypoxemia and suspected central airway obstruction, emergency flexible bronchoscopy was performed under general anesthesia via endotracheal intubation. Complete occlusion of the left main bronchus by thick mucus plugs was identified and successfully removed using suction and bronchoscopic forceps, resulting in immediate improvement in oxygenation and rapid radiologic lung re-expansion. The patient recovered fully and was discharged in 5 days without complications. This case highlights the importance of considering mucus plug-induced bronchial obstruction in toddlers presenting with sudden unilateral lung collapse and severe hypoxemia, particularly when foreign body aspiration remains a differential diagnosis. Early bronchoscopic intervention can be lifesaving and may prevent prolonged respiratory failure and associated complications.