Distribution of survival times after injury

Introduction: The distribution of survival times after injury has been described as “trimodal”, but several studies have not confirmed this. Methods: We constructed histograms for declared survival times (ts)<=50 minutes from the 2004-2007 Fatality Analysis Reporting System (FARS, for traffic crashes) and National Violent Death Reporting System (NVDRS, for homicides). EMS response times (tr) were also obtained when available. We estimated statistical models where death times were interval-censored on the range (tr, ts) for hospital cases and (0, tr) for non-hospital cases. For validation, we obtained ts, tr, and prehospital times (tp) for decedents in the 2008 National Trauma Data Bank (NTDB) with ts<=50. We approximated times until circulatory arrest (ta) as tr for patients pulseless at the injury scene, tp for others pulseless at hospital admission, and ts for the rest. For any declared ts in NTDB, we calculated mean ta, and applied this estimate to hospital deaths in FARS or NVDRS. Results: FARS and NVDRS deaths were most frequent in the first few minutes. Both showed a second peak at 35-40 minutes after injury, corresponding to peaks in hospital deaths. Third peaks were not seen. The distributions of estimated ta did not show second peaks, and were similar to interval-censored estimates of ts. Conclusions: Temporary increases in frequency of survival times at 35-40 minutes are primarily artifacts created because declaration of death in hospitals is delayed until resuscitative attempts have ceased. Interval censoring methods are therefore useful for analysis of injury survival times.