Outcomes after helicopter versus ground emergency medical services for major trauma--propensity score and instrumental variable analyses: a retrospective nationwide cohort study.
BACKGROUND
Because of a lack of randomized controlled trials and the methodological weakness of currently available observational studies, the benefits of helicopter emergency medical services (HEMS) over ground emergency medical services (GEMS) for major trauma patients remain uncertain. The aim of this retrospective nationwide cohort study was to compare the mortality of adults with serious traumatic injuries who were transported by HEMS and GEMS, and to analyze the effects of HEMS in various subpopulations.


METHODS
Using the Japan Trauma Data Bank, we evaluated all adult patients who had an injury severity score ≥ 16 transported by HEMS or GEMS during the daytime between 2004 and 2014. We compared in-hospital mortality between patients transported by HEMS and GEMS using propensity score matching, inverse probability of treatment weighting and instrumental variable analyses to adjust for measured and unmeasured confounding factors.


RESULTS
Eligible patients (n = 21,286) from 192 hospitals included 4128 transported by HEMS and 17,158 transported by GEMS. In the propensity score-matched model, there was a significant difference in the in-hospital mortality between HEMS and GEMS groups (22.2 vs. 24.5%, risk difference -2.3% [95% confidence interval, -4.2 to -0.5]; number needed to treat, 43 [95% confidence interval, 24 to 220]). The inverse probability of treatment weighting (20.8% vs. 23.9%; risk difference, -3.9% [95% confidence interval, -5.7 to -2.1]; number needed to treat, 26 [95% confidence interval, 17 to 48]) and instrumental variable analyses showed similar results (risk difference, -6.5% [95% confidence interval, -9.2 to -3.8]; number needed to treat, 15 [95% confidence interval, 11 to 27]). HEMS transport was significantly associated with lower in-hospital mortality after falls, compression injuries, severe chest injuries, extremity (including pelvic) injuries, and traumatic arrest on arrival to the emergency department.


CONCLUSIONS
HEMS was associated with a significantly lower mortality than GEMS in adult patients with major traumatic injuries after adjusting for measured and unmeasured confounders.
['Tsuchiya|Asuka|A|', 'Tsutsumi|Yusuke|Y|', 'Yasunaga|Hideo|H|']
D000293:Adolescent D000328:Adult D000368:Aged D000369:Aged, 80 and over D017732:Air Ambulances D000401:Aircraft D016208:Databases, Factual D004632:Emergency Medical Services D005260:Female D005500:Follow-Up Studies D017052:Hospital Mortality D006801:Humans D015601:Injury Severity Score D007564:Japan D008297:Male D008875:Middle Aged D009104:Multiple Trauma D012189:Retrospective Studies D014193:Trauma Centers D055815:Young Adult
Ground emergency medical service Instrumental variable Helicopter emergency medical service Trauma Mortality Japan Trauma Data Bank Propensity score