Air versus ground transport of the major trauma patient: a natural experiment.

Objectives: 1) To compare the outcomes of adult trauma patients transported to a level I trauma center by helicopter vs. ground ambulance. 2) To determine whether using a unique "natural experiment" design to obtain the ground comparison group will reduce potential confounders.

Methods: Outcomes in adult trauma patients transported to a tertiary care trauma center by air were compared with outcomes in a group of patients who were accepted by the online medical control physician for air transport, but whose air missions were aborted for aviation reasons (weather, maintenance, out on a mission); these patients were subsequently transported by ground ambulance instead. Outcomes were also analyzed for a third ground control group composed of all other adult trauma patients transported by ground during this time period. Data were collected by retrospective database review of trauma patients transferred between July 1, 1997, and June 30, 2003. Outcomes were measured by Trauma Injury Severity Score (TRISS) analysis. Z and W scores were calculated.

Results: Three hundred ninety-seven missions were flown by LifeFlight during the study period vs. 57 in the clinical accept-aviation abort ground transport group. The mean ages, gender distributions, mechanisms of injury, and Injury Severity Scores (ISSs) were similar in the two groups. Per 100 patients transported, 5.61 more lives were saved in the air group vs. the clinical accept-aviation abort ground transport group (Z = 3.37). As per TRISS analysis, this is relative to the expected mortality seen with a similar group in the Major Trauma Outcomes Study (MTOS). The Z score for the clinical accept-aviation abort ground transport group was 0.4. The 1,195 patients in the third all-other ground control group had a higher mean age, lower mean ISS, and worse outcomes according to TRISS analysis (W = -2.02).

Conclusions: This unique natural experiment led to better matched air vs. ground cohorts for comparison. As per TRISS analysis, air transport of the adult major trauma patient is associated with significantly improved survival as compared with ground transport.