A New Model for Evaluating the Impact of Major System Changes on Emergency Air Medical Scene Responses in a Regional EMS System

Hypothesis: Centralized dispatch data can provide useful information regarding the impact of major air medical system changes in a regional emergency medical services (EMS) system. Methods: Prospective evaluation of helicopter dispatch data from a centralized EMS dispatch agency. During the study period, four alterations in the total number of helicopters available to the system occurred (1, 2, 3, 2, 3). Statistical analysis consisted of Chi-Square with Yates’ correction and comparison of sample proportions with p<. 05 considered significant. Results A total of 667 helicopter dispatches occurred during the 20-month study period from April 1989 through November 1990. Helicopters Dispatches Days of Patients Cancellation Available Per Day Utilization Per Day Rate 1 0.66 39% 0.30 55% 2 0.96 50% 0.43 56% 3 1.50 ‘74% 0.74 51% p-value <.01 <.01 <.01 0.474 Conclusion: Changes in dispatch patterns could result either from increased availability or alterations in the dispatchers’ “threshold” for use based upon a perceived lessening of the need to save a “scarce” resource. Had the second possibility played a significant role, the rate of cancellation by ground personnel after arrival at the scene would be expected to have increased. Since this did not OCCUI, it is likely that the increased use actually was a result of increased availability. In systems that dispatch helicopters prior to arrival of ground personnel, this method of evaluation may provide a useful model for analyzing the impact of major system alterations.