Clinical Investigations Ultrasound diagnosis of occult pneumothorax*

Pneumothorax is a common problem seen in patients with both acute and chronic medical and traumatic conditions. Its frequency in the intensive care unit (ICU) is estimated at 6% (1). Chest radiography, a familiar technique (2), is the primary diagnostic modality used to screen for pneumothorax, but it has imperfect sensitivity for the disease: Misdiagnosis occurs in 30–40% of patients (3–7). Missed pneumothorax can have dramatic consequences in high-risk patients (8, 9). Half of radioccult cases yield tension pneumothorax (4). Even a tension pneumothorax can be radioccult (10), and delay in diagnosis will have deleterious consequences (11). Computed tomography (CT), the current gold standard, solves this problem but introduces major drawbacks (transfer of critically ill patients, delay, irradiation, and cost, among others), whereas the excessive search for pneumothorax has similar drawbacks (12). Hence, an immediately implemented technique at the bedside should be of interest in this setting. Could ultrasound play such a role? Its potential to examine the lung is classically thought to be limited, since air is considered an insurmountable obstacle. The image is thus exclusively composed of artifacts. However, a growing body of experience has shown that sonographic demonstration of the presence or absence of these artifacts can be used to aid in the diagnosis of a number of pulmonary diseases, including pleural effusion, alveolar consolidation, pulmonary edema, and pneumothorax (13). There is also the potential, based on our own and others’ clinical experience, that ultrasound may be more accurate than bedside radiography (14–18). This study describes the role of ultrasound in the identification of occult pneumothorax.