Abstract
Cleared For Takeoff: The Effects of Hypobaric Conditions on Traumatic Pneumothoraces
Current guidelines from the Aerospace Medical Association recommend not traveling on commercial flights after a traumatic pneumothorax (tPTX) until 2 weeks after full radiographic resolution of the tPTX; however, this recommendation is largely based on expert opinion and case studies. According to Boyle’s Law, there could be a 30% increase in the size of the pneumothorax during flight, possibly resulting in hypoxia, respiratory distress, and tension pneumothorax. It has been theorized that after a tPTX, patients are less tolerant of hypoxia at high altitudes and could possibly reopen a previously closed bronchopulmonary fistula.
This prospective observational study was performed at a level 1 trauma center in Salt Lake City, Utah. Twenty patients who had a unilateral tPTX treated with either a chest tube or high-flow oxygen were enrolled in the study. The study consisted of 2 phases. Phase 1 simulated typical cabin pressures for domestic flights by placing study subjects in a hypobaric chamber simulated at approximately 8400 feet (barometric pressure of 554 mm Hg). Phase 2 exposed study subjects to a simulated altitude of 12 650 feet (471 mm Hg) to mimic the typical change in pressure for a domestic flight, while also compensating for Salt Lake City’s higher starting elevation at 4200 feet. During the study, vital signs were closely monitored, and symptoms were assessed every 10 minutes during the simulated flight. Chest radiograph was obtained on hospital admission, before entering the hypobaric chamber, while at “altitude,” and 4 hours after the completion of the study.
Of the 20 patients enrolled in the study, the average injury severity score was 12.7, 80% were male, and 14 patients had a chest tube placed during initial management that was removed before the simulated flight. Although there was radiographic evidence of increased size of the tPTX (phase 1, 122%; phase 2, 171%), follow-up radiographs 4 hours after flight demonstrated a return to baseline tPTX size. Half the study subjects required supplemental oxygen in phase 1 to maintain oxygen saturations greater than 88%; however, the investigators note this population had associated injuries such as rib fractures or pulmonary contusions. All phase 2 study subjects were required to use supplemental oxygen owing to physiologic hypoxia at 12 650 feet. For all study subjects in both phases, there was no reported change in symptoms, no development of a tension pneumothorax, and no required procedural intervention. Limitations of the study include a small sample size, a simulated flight experience, and a higher baseline elevation in Salt Lake City, Utah. The investigators conclude that although there is a small increase in the size of tPTX in a simulated flight, it did not produce significant clinical adverse effects; however, supplement oxygen should be considered for patients with concomitant injuries. Finally, the investigators believe that current air travel recommendations after tPTX should be reconsidered, and future studies are needed.
(J Trauma Acute Care Surg. 2014;77:729–733). S Majercik, TW White, DH Van Boerum, et al.
Prepared by Wendy Hanna, MD, University of Utah Emergency Medicine Resident, Salt Lake City, UT, USA.