Impact of a New 9-1-1 Dispatch System on Call-Processing Times for Time-Critical Emergencies in the City of Los Angeles.

To determine the impact of a new emergency medical services (EMS) 9-1-1 dispatch system on call-processing times for field-confirmed time-critical emergencies. An interrupted time series study compared 9-1-1 calls for field-confirmed emergencies processed by Los Angeles Fire Department (LAFD)-telecommunicators using either the Medical Priority Dispatch System® (January 1 - September 30, 2014) or the new Los Angeles Tiered Dispatch System (January 1 - September 30, 2015). Prior to the study, authors identified seven categories of time-critical emergencies. Cases meeting inclusion criteria were systematically identified using LAFD electronic health records, and the elapsed time from call receipt to key events were obtained. The primary outcome was call-processing time (CPT), defined as time from 9-1-1 call receipt to when resources were dispatched. During the study period, 12,439 incidents met inclusion criteria: 6,208 using MPDS and 6,231 using LA-TDS. Among all unique time-critical incidents, the mean CPT was 16 seconds faster using LA-TDS (M = 68.5) compared to MPDS (M = 84.4; p < 0.001). CPT was significantly (p < 0.01) lower using LA-TDS for: cardiac arrests with attempted resuscitation, patients requiring ventilation support, seizures requiring prehospital benzodiazepines, gunshot wounds with hypotension, automobile vs. pedestrian accidents, and long falls. There was no difference in CPT for drownings requiring resuscitation (p = 0.60). The elapsed time to arrival of first responders on scene improved from 370.1 seconds using MPDS to 354.8 seconds using LA-TDS (p < 0.001). The new Los Angeles Tiered Dispatch System significantly improved 9-1-1 call-processing times and total response times for nearly all identified time-critical emergencies under study.