Estimating the effect of emergency care on early survival after traffic crashes

•Disparities in crash survival may be partly due to differences in EMS quality and response times.•Survival analysis can consider EMS effects as time-varying covariates.•Survival analysis is complicated by uncertainty in determining exact time of death.•Analytic difficulties can be managed using interval censoring and an imputation method.•Rural/urban survival disparity appears mostly unrelated to EMS quality or response times.

IntroductionTraffic crash mortality is higher in rural areas, but it is unclear whether this is due to greater injury severity, time delays, or Emergency Medical Services (EMS) deficiencies.MethodsData from 2002–2003 were combined from the Fatality Analysis Reporting System (FARS) and an “expanded version” of the National Automotive Sampling System (NASS) Crashworthiness Data System (CDS). Weighted Cox and Weibull models for survival time (tSURV) were estimated, with time-varying covariates (TVC) having constant effects for specified time intervals following EMS arrival time (tEMS) and hospital arrival time (tHOS). The Weibull model was repeated with tSURV interval-censored to reflect uncertainty about the exact time of death, using an imputation method to accommodate interval censoring along with TVC.ResultsFARS contained records for 92,718 persons with fatal or incapacitating injuries, and NASS/CDS contained 5517 (weighted population of 642,716) with incapacitating injuries. All models associated mortality with increasing age, male sex, belt nonuse, higher speeds, and vehicle rollover. The interval-censored model associated EMS intervention with a beneficial effect until tEMS + 30 min, but not thereafter; hospital intervention was associated with a strongly beneficial effect that increased with time. Rural location was associated with a higher baseline hazard; a 50% reduction in rural prehospital time would theoretically reduce 4-h mortality by about 7%.ConclusionRural/urban disparity in crash mortality is mostly independent of time delays and EMS effects. However, survival models with TVC support clinical intuition of a “golden hour” in EMS care, and the importance of timely transport to a hospital.