A 26-Year-Old Man Who Has Been in a Motor Vehicle Collision

Sara W. Nelson, MD; Daniel M. Lindberg, MD

Disclosures

August 31, 2016

The epidemiology of traumatic pneumothoraces has not been well characterized. In the United States, trauma is the leading cause of death in persons younger than 45 years and accounts for approximately 150,000 deaths annually.[1] The overall mortality for thoracic trauma is 10%, and chest injuries cause approximately 1 in 4 trauma deaths in North America.[2] Pneumothorax is a serious complication of thoracic trauma and has been described in 1 in 5 patients that survive major trauma.[3] Of note, in one study, 12% of patients with asymptomatic chest stab wounds had a delayed pneumothorax or hemothorax.[4]

Although pneumothoraces in stable patients can be confirmed radiographically, a tension pneumothorax that causes hemodynamic compromise should be diagnosed clinically, and treatment should never be delayed in favor of diagnostic imaging. A chest radiograph may reveal a linear shadow of visceral pleura, without lateral lung markings. An upright chest radiograph is more sensitive than a supine radiograph, as air tends to accumulate at the lung apex. In recumbent patients, air often accumulates in the anterior portion of the inferior chest and manifests radiographically as a "deep sulcus." If a pneumothorax without tension physiology is suspected but not seen on the initial upright chest radiography, a repeat film during exhalation may reveal it.

Increasingly, ultrasound is being used as a rapid bedside modality for diagnosing pneumothoraces; the literature suggests that chest ultrasonography by an emergency department physician is sufficient to rule out or rule in a pneumothorax.[5,6,7,8] CT scanning is more sensitive and specific than chest radiography or ultrasonography for the evaluation of small pneumothoraces and hemothoraces.

Occult pneumothoraces may be present in 2%-55% of trauma patients, although the clinical significance of occult pneumothoraces in patients who are not mechanically ventilated under positive pressure is unclear.[9] Making the diagnosis of hemothorax may be more challenging. A minimum of 200-300 mL of blood is needed in the pleural space for blunting of the costophrenic angle to be visible on an upright chest radiograph. Blood is more difficult to appreciate on a supine radiograph because it will typically layer posteriorly, and ever larger volumes (up to 1000 mL) of blood may produce only a mild diffuse radiodensity.

Lateral chest films may help differentiate hemothoraces from pulmonary contusions, and ultrasonography may also be useful for detecting fluid above the diaphragm. As with pneumothoraces, CT scanning is the most sensitive modality for diagnosing hemothoraces, although patients with massive hemothoraces may be too unstable for the scan.

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