Discussion
In this study, we sought to investigate the effect of transport times on trauma outcomes and if there were any differences between air and ground ambulances. Although it may appear intuitive that HEMS would lead to better patient outcomes when compared with GA, the topic has been hotly debated. Some studies show improved patient outcomes with shorter transport times.8–10 Kotwal et al investigate prehospital time in trauma patients on the battlefield between 2001 and 2014 and found an association between shorter prehospital transport time and decreased mortality, despite a simultaneous increase in ISS over the years as warfare injuries evolved.10 Other studies suggest that extended transport time does not lead to poorer outcomes.11–13 Newgard et al assessed the “Golden Hour” in EMS and found that shorter prehospital times were associated with no survival benefit among injured adults, a finding that persisted across many subgroups, including level of first responding EMS provider, mode of transport, country, age, injury type, and more severe physiologic derangement.11 Brown et al investigated prehospital time in trauma patients between GA and HEMS transport and found that HEMS only increased survival between 6 and 30 min of prehospital transport time, whereas transport time less than 5 min and greater than 30 min was not impacted by transport type.12 Our results indicate that trauma patients transported by HEMS were 57.0% less likely to die than those transported by GA after adjusting analysis for confounders.
The faster the ambulance is able to reach the trauma victim, the quicker medical treatment may be initiated. The short time period immediately after traumatic injuries may be the most deciding factor of mortality, especially in patients with wounds that need immediate care, such as rapid exsanguination. It has been shown that proximity to an airbase, and therefore a shorter dispatch time, is associated with reduced mortality in trauma patients.14 Since helicopters are often capable of arriving to the scene before a ground vehicle, it seems probable that this is one of the major factors responsible for the reduced mortality with HEMS. However, it should be noted that we do not have data for on-scene arrival times and therefore must limit our speculation.
In the HEMS cohort, we observed a 58.4% longer total prehospital time compared with the GA cohort. This is likely due to helicopters having to travel greater distances and rescuing more severely injured patients. Trauma patients who are more seriously wounded may require additional interventions or advanced life-saving procedures that increase total prehospital time. For example, the patient may need immediate intubation or extrication from a vehicle. Every effort should be made to minimize the time required to transport the patient back to the hospital.
Two noteworthy demographic differences between HEMS and GA populations were observed. There was a significantly greater proportion of whites and men in the helicopter group compared with the GA group. This may be related to HEMS being utilized more frequently in rural areas.
The findings in our study confirm our hypothesis that air transportation of trauma victims is associated with better patient outcomes. This is an expected finding since HEMS travel much faster than GA (and thus can arrive and provide care faster than GA) and contain better trained medical professionals. Despite these advantages, helicopters are unlikely to replace ground-based transport due to their exorbitant cost and inability to provide care in highly dense cities. Deeper investigation of this topic should seek to further refine our understanding of the differences between ground and air emergency transportation so that we can maximize patient outcomes while minimizing superfluous spending.
Limitations
There are some limitations to our study. First, these results stem from a center with a large proportion of rural transfers in a wide geographic area and is not generalizable to densely populated urban settings. Second, this study used the NTDB database which does not have data on prehospital deaths; thus, deaths occurring before access to EMS are not captured. Third, this study is a retrospective analysis using the NTDB. Some data (such as extrication times, specific life-saving interventions, and ongoing cardiopulmonary resuscitation in transport) would have enhanced our study but were unavailable in the NTDB. Fourth, the HEMS cohort demographic may not be representative of the general population. Fifth, we were limited to using ISS and trauma severity indexes to categorize injuries; more specific information regarding injury pattern (eg, blunt vs penetrating trauma) may help elucidate more specific findings. Sixth, we recognize that in both HEMS and GA cohorts, the mean total prehospital time was beyond the “Golden Hour”. This finding may be influenced by a difference in penetrating and blunt injuries, but a subset analysis investigating this disparity was beyond the scope of this study.