This was a prospective observational study approved by the institutional review board. The study was performed for educational purposes at a suburban Level 1 regional trauma center with an annual census of approximately 68,000 patients per year. The emergency department has its own affiliated EMS ambulance system. The study participants were 33 EMS providers, all with no previous ultrasound experience and varying levels of EMS experience. Each participant was given a brief 10-min lecture covering the use of ultrasound in detecting pneumothorax. Pneumothorax was identified by the lack of sliding between the visceral and parietal pleural layers (visualized as hyperechoic lines) with no distal reverberation artifact. Normal lung was defined as the presence of sliding with reverberation distal to the pleural line (Fig. 1). The lecture discussed basic principles of ultrasound physics, scanning techniques, and demonstrated video clips depicting both normal lung sliding and pneumothorax.
Each participant was then given an identical examination consisting of 20 video clips (10 positive for pneumothorax, 10 negative) and was asked if a pneumothorax was present in each individual clip. All video clips of pneumothoraces were recorded via DVD from actual patients who presented to the emergency department during the previous year. All patient identifiers were removed from the video prior to the initiation of the testing. Pneumothorax was confirmed in these patients by standard chest X-ray or chest CT. The control or “normal” video clips were obtained by imaging healthy volunteers (authors).
A high-frequency linear array transducer was used for each examination on either a SonoSite MicroMaxx (Bothell, WA), GE LOGIQ P5 (Milwaukee, WI), or Zonare Ultra System (Mountain View, CA). At our institution, physicians are taught to scan the lungs using this probe type due to the detailed resolution it offers. Others have preferentially selected other transducers in the evaluation for pneumothorax; however, we feel that at this time point the linear array probe is available on most ultrasound systems purchased by emergency departments, can be accessed in a rapid manner on most systems that have multiple active ports, and should yield the best results for this particular focused examination.
Study measurements
The study participants were instructed to use the presence or absence of lung sliding and reverberation artifact as the sole criteria for the diagnosis of pneumothorax. No other advanced techniques were depicted in the video clips (such as M-mode, powerslide sign, identification of lung point). Answers were recorded by each participant simply as “yes” or “no”. Data were collected on standardized answer sheets and later pooled for analysis.
Statistical methods
We used standard 2 × 2 tables to measure sensitivity, specificity, positive predictive value, and negative predictive value with corresponding confidence intervals (CIs).