CXR or USS in chest trauma for diagnosing pneumothorax

A recent Cochrane review in 2020 examined 13 studies to compare chest radiograph and ultrasound in trauma for diagnosing pneumothorax. 9 of these studies used patients as the units of analysis (410 traumatic pneumothorax patients out of 1271 patients). These were included in the primary analysis.

The remaining four studies used lung field as the unit of analysis and were included in the secondary analysis. The reviewers judged all studies to be at high or unclear risk of bias in one or more domains, with most studies (11/13, 85%) being judged at high or unclear risk of bias in the patient selection domain. There was substantial heterogeneity in the sensitivity of supine CXR amongst the included studies.¹⁰

In the primary analysis, the summary sensitivity and specificity of chest ultrasound were 0.91 (95% CI 0.850.94) and 0.99 (95% CI 0.971.00); and the summary sensitivity and specificity of supine CXR were 0.47 (95% CI 0.310.63) and 1.00 (95% CI 0.971.00). Chest ultrasound was significantly more sensitive than CXR, while the specificities were very similar.

The authors of this study go on to explain that in a hypothetical cohort of 100 patients if 30 patients have traumatic pneumothorax (i.e. a prevalence of 30%), chest ultrasound would miss 3 (95% CI 24) cases (false negatives) and over diagnose 1 (95% CI 02) of those without pneumothorax (false positives); while CXR would miss 16 (95% CI 1121) cases with 0 (95% CI 02) overdiagnosis of those who do not have pneumothorax.¹⁰