Case vignette
59yo M BIBA as a modified trauma after bicycle accident.
HR 110, BP 120/80, RR 22, SpO2 92% on RA, T 36.5
Primary survey: airway intact, breath sounds diminished on left, circulation intact
Secondary: L chest ecchymosis and crepitus, facial trauma. eFAST performed during secondary. Views from the anterior/superior L chest are shown.
What do you see?
Tr4 US1: no movement at pleural interface (lack of lung slide)
Tr4 US2: leading edge sign (pleural interface sliding in and out of view with inspiration)
What do you do next?
Identifying a traumatic pneumothorax, you note the patient is symptomatic and recommend a pigtail chest tube to the trauma team. You perform this at bedside, and the patient is taken to the CT scanner for further assessment.
Teaching points.
Ultrasound is highly sensitive for pneumothorax. The linear probe usually works best given higher frequency and better resolution at lower depth. (Both phased array and even curvilinear, for example in morbidly obese patients, can also be used.) The anterior/superior mid-clavicular chest is most sensitive (air rises!). Assess for pleural lung slide (sometimes described as "ants marching on a log"). No movement of the pleural interface is concerning for pneumothorax. Equivocal cases can be informed by using M-mode to assess motion over time. This is where the classic "sandy beach" vs "bar code" signs are seen.
Note that while US is sensitive for pneumothorax, absent lung slide alone is not specific. False positives can occur with apnea (no ventilation), splinting, blebs/bullae, adhesions (such as post VATS/pleurodesis), or chest tubes. With blebs/bullae, lung slide will be intact, but comet tails will never be present (as the lung parenchyma is gone).
The leading edge sign, however, IS very specific for pneumothorax. This occurs when the viscero-parietal pleural interface (the "ants marching on a log") slides into and out of view with inspiration.
Obtain a CXR and compare to prior imaging when possible/if there is uncertainty. In more complex (but sufficiently stable) patients, CT can be considered.
Note: in stable patients without substantial symptoms, a CXR should also be obtained before chest tube to assess pneumothorax size. Not all traumatic pneumothoraces require thoracostomy. In stable trauma patients without concurrent hemothorax and not on ventilation, recent literature suggests smaller pneumothoraces may be managed with observation alone. The proposed size cut off is 35mm (measured using the radial distance between the parietal and visceral pleura, perpendicular to the chest wall, at the largest air pocket). See the below reference.
Sources: Eddine, Boyle, Dodgion et al. Observing pneumothoraces: the 35-millimeter rule is safe for both blunt and penetrating chest trauma. J Trauma Acute Care Surg. 2018. 86(4):557-64.
Residents: Dr. Hannah Wolfer
Traumatic Pneumothorax
May 2018