Background and aim: Helicopter EMS (HEMS) is a well-established mode of rapid transportation for patients with need for time-sensitive interventions, especially in patients with significant traumatic injuries. Traditionally in the setting of trauma, HEMS is often considered appropriate when used for patients with "severe" injury as defined by Injury Severity Score (ISS) >15. This may be overly conservative, and patients with a lower ISS may benefit from HEMS-associated speed or care quality. Our objective was to perform a meta-analysis of trauma HEMS transports to evaluate for possible mortality benefit in injured cases defined by an ISS score >8, lower than the customary ISS cutoff of >15.
Methods: A broad search of the literature was performed including PubMed, EMBASE, SCOPUS, Cochrane Central Register of Controlled Trials, and Google Scholar from the years 1970 to 2022. The gray literature and reference lists of included publications were also examined. We included studies with the outcome of mortality in HEMS vs control in trauma transports from scene of injury for patients (adult or pediatric) with ISS > 8.
Results: Nine eligible studies were used in the final analysis: six in the primary analysis and three in sensitivity analysis due to patient overlap. All studies reported statistically significant survival benefit in HEMS compared to control group. The minimum survival odds ratio (OR) benefit observed was OR 1.15 (95% CI 1.06-1.25) and maximum was OR 2.04 (95% CI 1.18-3.57). Risk of bias tool (ROBINS-I) application yielded moderate to low risk of bias, mainly due to the observational nature of the studies included.
Conclusions: There was a statistically significant survival benefit in patients with ISS > 8 when HEMS was used over traditional ground ambulance transportation, although novel and more inclusive trauma triage criteria may be more appropriate in the future to guide HEMS utilization decision-making. Restricting HEMS to trauma patients with ISS >15 likely misses survival benefit that could be afforded to the subset of trauma patients with serious injury.