This report describes a patient with status asthmaticus and respiratory failure in whom profound hypoxemia developed during mechanical ventilation. During the hypoxemic episode, breath sounds were absent over the left lung, and chest radiography revealed a hyperlucent left hemithorax with tension shift of the mediastinum to the right. The presence of lung markings in the left lung on radiography eliminated the possibility of tension pneumothorax and led to the diagnosis of tension mediastinal shift secondary to a ball valve obstruction by a central mucus plug. Bronchoscopic lung lavage removed the mucus plug, thereby correcting the hypoxemia. Recognition of this previously undescribed acute complication of mechanical ventilation in status asthmaticus is essential so that confusion with tension pneumothorax is avoided and appropriate therapy instituted.
