The association between air ambulance distribution and trauma mortality.

Objective: To determine whether increasing distance between helicopter ambulance airbase and either home residence or referring facility is associated with an increased risk of injury-related mortality.

Background: A dramatic increase in the absolute number and utilization of Helicopter Emergency Medical Services transports has occurred in the management of the critically injured patients. HEMS are resource intensive, and the most efficient geographic distribution of airbases necessary to improve patient outcomes is unknown.

Methods: We performed a retrospective analysis of 244,293 adult trauma patients who were treated at a designated trauma center (TC) in Pennsylvania during the period 1997 to 2007, using the Pennsylvania Trauma Outcomes Study data set. We performed a multivariate analysis, adjusting for differences in case mix, to determine whether airbase proximity to either residence or referring facility is associated with injury-related mortality.

Results: For patients residing distant (>20 miles) from a TC, increasing distance from an airbase is associated with an increased risk of death; for each mile, the risk of mortality increases by approximately 1% (adjusted odds ratio, 1.011; 95% confidence interval, 1.002-1.018; P = 0.02). There is no additional benefit to living close (<25 miles) to more than 1 airbase. However, most airbases are positioned near TC and other airbases. Despite the proliferation of helicopter ambulances, 18.1% of patients who did not live near a TC also did not live near airbase.

Conclusions: For individuals residing distant from a TC, proximity to 1 airbase is associated with reduced risk of death. No additional benefit is observed when airbases are positioned close to a TC or other airbases.