Background: Although survival benefits have been shown at the population level, it remains unclear what drives the outcome benefits for helicopter emergency medical services (HEMS) in trauma. Although speed is often cited as the vital factor of HEMS, we hypothesized a survival benefit would exist in the absence of a time savings over ground emergency medical services (GEMS). The objective was to examine the association of survival with HEMS compared with GEMS transport across similar prehospital transport times.
Methods: We used a retrospective cohort of scene HEMS and GEMS transports in the National Trauma Databank (2007-2012). Propensity score matching was used to match HEMS and GEMS subjects on the likelihood of HEMS transport. Subjects were stratified by prehospital transport times in 5-minute increments. Conditional logistic regression determined the association of HEMS with survival across prehospital transport times strata controlling for confounders. Transport distance was estimated from prehospital transport times and average HEMS/GEMS transport speeds.
Results: There were 155,691 HEMS/GEMS pairs matched. HEMS had a survival benefit over GEMS for prehospital transport times between 6 and 30 minutes. This benefit ranged from a 46% increase in odds of survival between 26 and 30 minutes (adjusted odds ratio [AOR], 1.46; 95% CI, 1.11-1.93; P < .01) to an 80% increase in odds of survival between 16 and 20 minutes (AOR, 1.80; 95% CI, 1.51-2.14; P < .01). This prehospital transport times window corresponds to estimated transport distance between 14.3 and 71.3 miles for HEMS and 3.3 and 16.6 miles for GEMS.
Conclusion: When stratified by prehospital transport times, HEMS had a survival benefit concentrated in a window between 6 and 30 minutes. Because there was no time-savings advantage for HEMS, these findings may reflect care delivered by HEMS providers.
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