Background: Because of a lack of randomized controlled trials and the methodological weakness of currently available\nobservational studies, the benefits of helicopter emergency medical services (HEMS) over ground emergency medical\nservices (GEMS) for major trauma patients remain uncertain. The aim of this retrospective nationwide cohort study was\nto compare the mortality of adults with serious traumatic injuries who were transported by HEMS and GEMS, and to\nanalyze the effects of HEMS in various subpopulations.\nMethods: Using the Japan Trauma Data Bank, we evaluated all adult patients who had an injury severity score ââ?°Â¥ 16\ntransported by HEMS or GEMS during the daytime between 2004 and 2014. We compared in-hospital mortality between\npatients transported by HEMS and GEMS using propensity score matching, inverse probability of treatment\nweighting and instrumental variable analyses to adjust for measured and unmeasured confounding factors.\nResults: Eligible patients (n = 21,286) from 192 hospitals included 4128 transported by HEMS and 17,158 transported by\nGEMS. In the propensity score-matched model, there was a significant difference in the in-hospital mortality between\nHEMS and GEMS groups (22.2 vs. 24.5%, risk difference âË?â??2.3% [95% confidence interval, âË?â??4.2 to âË?â??0.5]; number needed to\ntreat, 43 [95% confidence interval, 24 to 220]). The inverse probability of treatment weighting (20.8% vs. 23.9%;\nrisk difference, âË?â??3.9% [95% confidence interval, âË?â??5.7 to âË?â??2.1]; number needed to treat, 26 [95% confidence\ninterval, 17 to 48]) and instrumental variable analyses showed similar results (risk difference, âË?â??6.5% [95% confidence\ninterval, âË?â??9.2 to âË?â??3.8]; number needed to treat, 15 [95% confidence interval, 11 to 27]). HEMS transport was significantly\nassociated with lower in-hospital mortality after falls, compression injuries, severe chest injuries, extremity (including\npelvic) injuries, and traumatic arrest on arrival to the emergency department.\nConclusions: HEMS was associated with a significantly lower mortality than GEMS in adult patients with major traumatic\ninjuries after adjusting for measured and unmeasured confounders.
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