Aim Time based standards have been used as a key performance measure for EMS internationally but can lead to operational behaviours that are not clinically focussed. NHS England tested a new operational model (Dispatch on Disposition) allowing additional call triage time of up to 4 min before starting the response interval clock start.

Method A controlled before and after time series analysis of the intervention implemented in 6 of the 10 regional EMS services. We measured weekly trends in average resource allocation per call and a range of time measures for different call types for 1 year before and 7 months after implementation, and used time series regression models to compare changes between intervention and control sites adjusted for seasonality, call volumes and hours lost at hospital handover.

Results The proportion of emergency calls responded to within 8 min increased by 6.6% in the intervention group. The 95th percentile time from call connecting to EMS and a resource arriving on scene reduced by 9.45 and 166.6 s for life-threatening and emergency calls respectively. There was a statistically significant reduction in average resources allocated per incident of −0.1 for life-threatening calls, −0.06 for emergency and −0.12 for urgent in the intervention group – equivalent to an additional 10 243 whole resources available to respond per week in England. There was no change in service re-contact.

Conclusion Additional call triage time does not lead to a reduction in response time performance, improves efficiency of resource use and is safe for patients.

Conflict of interest None

Funding NHS England.