Effect of new 9-1-1 system on efficiency of initial resource assignment.

Objective: To determine the impact of a new dispatch system on the efficiency of first resource assignment for critical EMS patients. Methods: In December 2014, the Los Angeles Fire Department (LAFD) implemented a new, internally-developed dispatch system. An interrupted time series study compared 9-1-1 incidents processed by LAFD-telecommunicators using either the Medical Priority Dispatch System® (MPDS, January 1 - September 30, 2014), or Los Angeles Tiered Dispatch System (LA-TDS, January 1 - September 30, 2015). All incidents were assigned a Dispatch Level of Service (DLOS), based on whether a basic life support (BLS) or advanced life support (ALS) resource was dispatched, and a Field-Recommended Level of Service (RLOS), a metric based on medical necessity, required scope of practice, number and intensity of interventions, and patient severity. DLOS options included BLS or ALS, whereas RLOS options included BLS, ALS1 and ALS2, with ALS2 cases having the greatest medical need. The primary outcome was critical under-triage rate, and secondary outcomes included rates of over-triage, total resource utilization and test characteristics of each dispatch system. Results: 563,188 incidents met inclusion criteria, including 271,604 using MPDS and 291,584 using LA-TDS. During the MPDS period, 96,561 (35.6%) incidents were initially dispatched with BLS resources (including 194 (0.071% ultimately found in the field to be high-acuity RLOS ALS2), and 175,043 were dispatched with ALS resources. During the LA-TDS period, 127,827 (43.8%) were dispatched as BLS (including 154 RLOS ALS2) and 163,798 were dispatched as ALS. For the primary outcome, the critical under-triage rate was 0.20% using MPDS and 0.12% using LA-TDS (Z 4.7, p < 0.0001, RR 0.61 CI 95% 0.50-0.76), and this improvement was primarily driven by improved triage of cardiac arrest. The over-triage rate using MPDS was 44%, which decreased to 33% using LA-TDS. LA-TDS was associated with significant improvements in specificity, positive predictive value and accuracy of initial resource assignment, and is projected to have saved over 23,000 EMS resource dispatches over the 9-month study period. Conclusion: The new Los Angeles Tiered Dispatch System significantly improved the efficiency of initial 9-1-1 resource assignments by decreasing both over-triage and critical under-triage, thus sending more appropriate resources to each 9-1-1 call.