A tension pneumothorax occurs when air enters the pleural space and cannot escape, creating progressively rising intrathoracic pressure. MCCQE objectives emphasize rapid recognition of life-threatening causes of respiratory distress based on bedside findings. As pressure builds, the affected hemithorax compresses the lung and pushes the mediastinum to the opposite side, producing tracheal deviation away from the affected side —a classic, high-specificity sign of tension physiology (often accompanied by severe dyspnea, tachycardia, unilateral absent breath sounds, hyperresonance, distended neck veins, and hypotension from impaired venous return).

The other options do not specifically support tension pneumothorax: ecchymoses suggest trauma; bilateral wheezing suggests asthma or bronchiolitis; abdominal distension is nonspecific; inspiratory stridor indicates upper airway obstruction (e.g., croup, foreign body). Because tension pneumothorax is a clinical diagnosis, MCCQE priorities are immediate decompression (needle thoracostomy) followed by chest tube placement—without waiting for imaging if the child is unstable.