Emergency medical transport of trauma patients: A comparison of helicopter and ground ambulances

Emergency medical transport of trauma patients from the scene of injury is an integral part of any trauma system. The use of helicopter emergency medical services (HEMS) has been scrutinized because of high costs, unclear effectiveness, and an increase in deadly crashes. Previous studies evaluating the impact of HEMS transport on trauma mortality vary widely with respect to locale, patient population, methodology, and in their findings. Between-group differences among covariates that both influence the decision to use ground or HEMS transport and are related to mortality will confound the association of mode of transport and mortality. Using a case-control design and multivariable logistic regression, pre-hospital factors that influence the decision to use ground or HEMS transport were identified. Using the factors associated with the mode of transport, a propensity score was developed which was subsequently used in a Cox proportional hazards analysis of two-week mortality and mode of transport. The propensity score represented the conditional probability that a patient would be transported by HEMS and acted as a composite confounding variable or balancing score in the model of mortality. Adjusted for the propensity score, injury severity, revised trauma score, and distance from the trauma center, patients transported by HEMS had a 32% lower risk of mortality within two-weeks of arrival at the trauma center. However, numerous patients transported by HEMS had low injury severity and normal vital signs suggesting further improvements in triage and guidelines for HEMS use are needed.