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Pneumothorax volume expansion in helicopter emergency medical services transport
Derek Knotts1, Annette O Arthur, Peyton Holder
1Department of Emergency Medicine, University of Oklahoma School of Community Medicine and Hillcrest Medical Center, Tulsa, OK 74104, USA.
Objective:
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.
Methods:
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.
Results:
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.
Conclusion:
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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