A prospective comparison of supine chest radiography and bedside ultrasound for the diagnosis of traumatic pneumothorax

Background: Supine anteroposterior (AP) chest radiography may not detect the presence of a small or medium pneumothorax (PTX) in trauma patients. Objectives: To compare the sensitivity and specificity of bedside ultrasound (US) in the emergency department (ED) with supine portable AP chest radiography for the detection of PTX in trauma patients, and to determine whether US can grade the size of the PTX. Methods: This was a prospective, single-blinded study with convenience sampling, based on researcher availability, of blunt trauma patients at a Level I trauma center with an annual census of 75,000 patients. Enrollment criteria were adult trauma patients receiving computed tomography (CT) of the abdomen and pelvis (which includes lung windows at the authors' institution). Patients in whom the examination could not be completed were excluded. During the initial evaluation, attending emergency physicians performed bedside trauma US examinations to determine the presence of a sliding lung sign to rule out PTX. Portable, supine AP chest radiographs were evaluated by an attending trauma physician, blinded to the results of the thoracic US. The CT results (used as the criterion standard), or air release on chest tube placement, were compared with US and chest radiograph findings. Sensitivities and specificities with 95% confidence intervals (95% CIs) were calculated for US and AP chest radiography for the detection of PTX, and Spearman's rank correlation was used to evaluate for the ability of US to predict the size of the PTX on CT. Results: A total of 176 patients were enrolled in the study over an eight-month period. Twelve patients had a chest tube placed prior to CT. Pneumothorax was detected in 53 (30%) patients by US, and 40 (23%) by chest radiography. There were 53 (30%) true positives by CT or on chest tube placement. The sensitivity for chest radiography was 75.5% (95% Cl = 61.7% to 86.2%) and the specificity was 100% (95% Cl = 97.1% to 100%). The sensitivity for US was 98.1% (95% CI = 89.9% to 99.9%) and the specificity was 99.2% (95% Cl = 95.6% to 99.9%). The positive likelihood ratio for a PTX was 121. Spearman's rank correlation showed at p of 0.82. Conclusions: With CT as the criterion standard, US is more sensitive than flat AP chest radiography in the diagnosis of traumatic PTX. Furthermore, US allowed sonologists to differentiate between small, medium, and large PTXs with good agreement with CT results.