Factors Influencing the Timeliness of Emergency Medical Service Response to Time Critical Emergencies

Objective: While emergency medical service (EMS) response times (ERT) remain a leading measure of system performance in many developed countries, relatively few studies have explored the factors associated with meeting benchmark performance for potentially time critical incidents. The purpose of this study was to identify system-level and patient-level factors associated with ERT, which are readily available at the time of ambulance dispatch. Methods: Between July 2009 and June 2014, we included data from 1,000,458 EMS responses to time critical “lights and sirens” incidents in Melbourne, Australia. The primary outcome measure was ERT, defined as the time from emergency call to the arrival of the first EMS team on scene. Quantile regression models were used to identify system-level and patient-level factors associated with 10-percentile intervals of ERT. Results: The median ERT was 10.6 minutes (IQR: 8.1–14.0), increasing from 9.6 minutes (IQR: 7.6–12.5) in 2009/10 to 11.0 minutes (IQR: 8.4–14.7) in 2013/14 (p < 0.001). System-level factors independently associated with the 90th percentile ERT were distance to scene, activation time, turnout time, case upgrade, hour of day, day of week, workload in the previous hour, ambulance skill set, priority zero case (e.g., suspected cardiac or respiratory arrest), and average hospital delay time in the previous hour. Patient-level factors such as age, gender, chief medical complaint, and severity of complaint were also significantly associated with ERT. Conclusions: System-level and patient-level factors available at the time of ambulance dispatch are useful predictors of ERT performance, which could be used to improve the timeliness of EMS response.