pulmonary disorders
Pneumothorax
Diagnosis of Pneumothorax
Chest imaging The diagnosis is suspected in patients whose condition is stable but who have dyspnea or pleuritic chest pain and is usually confirmed with upright inspiratory chest x-ray. Radiolucent air and the absence of lung markings juxtaposed between a shrunken lobe or lung and the parietal pleura are diagnostic of pneumothorax. Tracheal deviation and mediastinal shift occur with large pneumothoraces. The diagnosis can also be made using bedside ultrasonography in the absence of underlying lung disease. The size of a pneumothorax is defined as the percentage of the hemithorax that is vacant. This percentage is estimated by taking 1 minus the ratio of the cubes of the width of the lung and hemithorax. For example, if the width of the hemithorax is 10 cm and the width of the lung is 5 cm, the ratio is 53/103=0.125. Thus, the size of the pneumothorax is about 1 minus 0.125, or 87.5%. If adhesions are present between the lung and the chest wall, the lung does not collapse symmetrically, the pneumothorax may appear atypical or loculated, and the calculation is not accurate. Small pneumothoraces (eg, < 10%) are sometimes overlooked on chest x-ray. In patients with possible pneumothorax, lung markings should be traced to the edge of the pleura on chest x-ray. Conditions that mimic pneumothorax radiographically include emphysematous bullae, skinfolds, folded bed sheets, and overlap of stomach or bowel markings on lung fields. Sudden hypotension in a mechanically ventilated patient should prompt consideration of tension pneumothorax. If the patient also has decreased breath sounds and hyperresonance to percussion, tension pneumothorax should be presumed and treated immediately without awaiting confirmation by chest x-ray. 