eFAST: when trauma ultrasound also looks at the chest

How the thoracic extension of FAST identifies pneumothorax and pleural effusion at the bedside, with the key ultrasound signs and the accuracy reported in the literature.

Classic FAST was designed to answer an abdominal and pericardial question: is there free fluid where there shouldn't be? But trauma rarely respects anatomical boundaries, and a large share of polytrauma patients also have thoracic involvement. That's where eFAST comes in — Extended Focused Assessment with Sonography for Trauma — which adds a targeted search for pneumothorax and hemothorax/pleural effusion to the traditional assessment, requiring little more than a few extra minutes of exam time.

Technique: assessing pneumothorax

The lung window is obtained by placing the transducer — high-frequency linear or curvilinear — in the 2nd or 3rd intercostal space, along the midclavicular line, in a sagittal orientation. This is the so-called anterior window, where free air in the pleural space tends to accumulate first with the patient supine. The rib–pleura–rib profile seen on B-mode resembles the silhouette of a bat with its wings spread — the bat sign — an anatomical landmark that confirms correct positioning over the pleural line.

Under normal conditions, the visceral pleura slides over the parietal pleura with every respiratory cycle, generating a shimmering pattern just below the pleural line — classically described as the ants marching sign. In practice, the presence of lung sliding rules out pneumothorax at that specific examined point.

Freezing the image in M-mode over the pleural line, the normal pattern shows a granular texture below the pleura, resembling a beach — the seashore sign. In the absence of pleural sliding, suggestive of pneumothorax, this pattern becomes a series of parallel horizontal lines, the barcode sign (or stratosphere sign).

The lung point is the transition point between the area of lung still adherent to the chest wall — with lung sliding present — and the collapsed lung area, without sliding. When identified, it's considered 100% specific for pneumothorax; its absence, however, doesn't rule out the diagnosis, since large pneumothoraces may not present a visible transition point in the examined field.

Pleural effusion and hemothorax

Hemothorax assessment uses the same window used for the lung bases in the abdominal FAST — the hepatorenal and splenorenal windows, extended cranially above the diaphragm. The finding is the presence of an anechoic collection (or hypoechoic, when there's clot) in the pleural space, often associated with the spine sign: visualization of the spine above the diaphragm, which is normally obscured by aerated lung.

Accuracy: what the literature shows

This is one of the points where eFAST stands out consistently in the literature, mainly because conventional chest X-ray has low sensitivity for anterior pneumothorax in the supine patient — exactly the most common scenario in acute trauma. A recent prospective study of hemodynamically stable patients with blunt thoracoabdominal trauma found, for thoracic injuries identified by eFAST, a sensitivity of 87.2% (95% CI 77.9–93.4%), specificity of 100% (95% CI 91.6–100%), positive predictive value of 100%, and negative predictive value of 80.8%. In that same study, ultrasound identified 68 of 78 confirmed thoracic injuries, versus only 32 detected by conventional X-ray — a statistically significant difference (p < 0.001) — and every patient who went on to require pleural drainage or laparotomy already had a positive eFAST finding.

For pneumothorax specifically, the emergency and critical care literature consistently describes ultrasound as more sensitive and more reliable than physical exam alone, with the specificity of the lung point approaching 100% when present — a finding reinforced by systematic reviews dedicated to comparing thoracic ultrasound with X-ray for pneumothorax diagnosis in the emergency setting.

Limitations

The absence of lung sliding is not synonymous with pneumothorax: pleural adhesions, pulmonary fibrosis, mainstem intubation, apnea, and subcutaneous emphysema can also abolish pleural sliding without any free air in the pleural space, so the finding should always be interpreted in clinical context. A posterior or loculated pneumothorax may go undetected through the standard anterior window, especially in the supine patient, and extensive subcutaneous emphysema can completely prevent obtaining an adequate acoustic window. As with abdominal FAST, the method is operator-dependent, and the learning curve to reliably recognize the lung point, the barcode sign, and small effusions requires supervised training.

In an unstable polytrauma patient, waiting for a formal chest X-ray — often technically limited by supine positioning and the urgency of the scenario — can cost precious minutes. eFAST, performed at the bedside in just a few extra minutes beyond traditional FAST, allows clinically significant pneumothorax and hemothorax to be identified nearly in real time, guiding decisions such as thoracostomy, chest tube placement, or prioritizing transport for CT. Today, mastering its ultrasound signs — bat sign, lung sliding, seashore/barcode sign, lung point — is considered part of the standard initial assessment of the trauma patient in many international protocols.