Pneumothorax Volume Expansion in Helicopter Emergency Medical Services Transport



      In accordance with Boyle's law (as barometric pressure decreases, gas volume increases), thoracostomy is often recommended for patients with pneumothoraces before helicopter EMS (HEMS) transport. We sought to characterize altitude-related volume changes in a pneumothorax model, aiming to improve clinical decisions for preflight thoracostomy in HEMS patients.


      This prospective study used 3 devices to measure air expansion at HEMS altitudes. The main device was an artificial pneumothorax model that mimicked a human pulmonary system with a 40 mL pneumothorax. In addition, volume changes were calculated in 2 spherical balloons (6 L and 25 L) by measuring equatorial circumferences. Measurements were recorded at 500-foot altitude increments from 1000 to 5000 feet above ground level.


      The 3 models exhibited volume increases of 12.7%–16.2% at 5000 feet compared to ground level. Univariate linear regression yielded similar increases, 1.27%–1.52%, in volume per 500-foot altitude increase for all 3 models. Bivariate indexed linear regression identified no association between volume increase and assessment model (P values .19 and .29). Locally weighted scatterplot smoothing (lowess) plots indicated linearity of the altitude-volume relationship.


      This study demonstrated predictable pneumothorax volume changes at typical HEMS altitudes. Increased understanding of altitude-related volume changes will aid decision making before transport.
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