The impact of using time critical intervention-based dispatch thresholds on lowering lights and siren use to EMS 911...

Emergency Medical Services (EMS) has historically utilized lights and sirens (L&S) to respond to 911 incidents. L&S are used in 86% of scene responses nationally; however, time critical interventions (TCIs) occur in less than 7% of these incidents. Responses with L&S are associated with increased risk of crashes and injuries. Our objective was to determine the impact of TCI-based dispatch thresholds on L&S use, dispatch accuracy, and response times.

We performed a before-after retrospective evaluation of TCI-based dispatch methodology at a suburban EMS system. We categorized all EMS interventions as TCI or not, and we determined a TCI threshold above which we would use L&S. We then assigned response priorities to each call nature based on the proportion of TCIs within them. We compared historical results with those from the 6 months following implementation in terms of L&S use, dispatch accuracy, and response times.

There were 13,879 responses in the "before" group and 14,117 in the "after" group. The rate of L&S use decreased from 56.2% in the before group to 27.6% in the after group, while TCIs were performed in 6.9% of responses in the before group and 7.6% in the after group. Accuracy increased from 48.8% to 75.1% and median response time increased by 0.1 min from 8.3 to 8.4 min.

Using TCI-based dispatch thresholds, we decreased L&S use and increased accuracy with minimal increased response time. Our results support the use of this methodology to determine EMS response modes.