Background Ambulance services across the UK have recognised a clinical and operational problem with persistent high users of the 999 service, but there is a lack of evidence about what works in this setting and how. We aim to evaluate the effectiveness, safety and efficiency of multi-agency case management approaches to the care of people who frequently call the emergency ambulance service, and gain understanding of barriers and facilitators to implementation.

Methods We will carry out a mixed methods evaluation using anonymised linked routine data outcomes in a ‘natural experiment’ cohort design in four UK ambulance services, with one case management intervention site and one control site within each service. We will describe the epidemiology of ‘frequent calling’; assess the effects of case management on process, outcomes, safety and costs up to six months for 300 high users per service (n-1200); and examine the views of stakeholders, including patients, through qualitative methods. We will synthesise quantitative and qualitative findings, informed by a logic model describing predicted mechanisms of change.

Results We received confirmation of NIHR grant funding for this study in 2018 so do not yet have results to report.

Conclusions Telephone callers with sustained high needs represent a significant, high profile policy challenge to emergency ambulance services. Such callers may be indicative of gaps elsewhere in the health care system, which could be more effectively addressed by pro-active care. The STRETCHED study provides the opportunity to contribute to the currently sparse evidence base on interventions for this patient group.