J. B. Brown1, M. L. Gestring2, M. R. Rosengart1, A. B. Peitzman1, T. R. Billiar1, J. L. Sperry1 1University Of Pittsburgh,Department Of Surgery,Pittsburgh, PA, USA 2University Of Rochester,Department Of Surgery,Rochester, NY, USA
Introduction:
Helicopter transport (HT) following traumatic injury has been shown to improve survival; however the contibution of factors such as speed and crew resources are not clear. The study objective was to examine the impact of HT vs ground transport (GT) on survival across similar prehospital transport times (PHTT).
Methods:
Subjects >15 years undergoing HT or GT from the scene of injury in the National Trauma Databank (2007-2012) were included. Subjects were excluded if dead on arrival or missing PHTT. PHTT was stratified by 5min increments between 0 and 60mins. To account for differences between HT and GT groups, propensity score matching was used to estimate the probability of HT. Variables in the propensity-score included age, sex, prehospital vital signs, prehospital response and scene time, injury severity score, and mechanism of injury. 1:1 nearest neighbor matching was used to match HT and GT subjects on the probability of undergoing HT. Standardized differences were used to assess balance after matching. Conditional logistic regression was used to determine the association of HT vs GT with in-hospital survival across PHTT strata, controlling for ICU admission, emergent surgery, mechanical ventilation, and insurance status. False discovery rate correction was used for multiple comparisons. Transport distance was estimated from PHTT using national average HT and GT transport speeds.
Results:
156,010 pairs were matched, giving 312,020 subjects for analysis. The propensity score model had good discrimination (AUC=0.91). After matching, no variable in the propensity score had a standardized difference >0.2 with a 77% reduction in overall bias. HT subjects required ICU admission, emergent surgery, and mechanical ventilation more often than GT subjects (p<0.01). HT vs GT median prehospital response time (19min vs 19min) and scene time (14min vs 15min) were similar. Median PHTT in the HT group was 21min (IQR 16, 30) compared to 23min (IQR 15, 36) in the GT group (p<0.01). HT vs GT was independently associated with an increased odds of survival in a time window between 6 and 25mins (Fig). This corresponds to an estimated transport distance between 14.3 and 59.4mi for HT, and 3.3 and 13.8mi for GT. The survival benefit of HT peaked at a PHTT of 11-15min (OR 2.02; 95%CI 1.70-2.41, p<0.01).
Conclusion:
The survival benefit for HT in trauma at the population level is concentrated in a PHTT window between 6 and 25mins. These results highlight the importance of logistical considerations and the potential influence of crew resources on outcome for HT in trauma, with implications for trauma system design and planning. Further study of the interplay between transport time, distance, and survival for HT in trauma is warranted.
