Realist review protocol for understanding young people's experiences of engaging with police-mental health practitioner collaboration in emergency responses to mental health crises.

Background: Children and young people are facing increasing mental health challenges. Access to emergency mental health care for young people is under-researched and poorly understood. Police data indicates a rise in youth mental health emergency calls, but officers often feel unprepared to support young people in crisis. Mental health practitioners have the experience and training to provide helpful support to young people in crisis, although the availability of mental health services for young people can be limited during evenings and weekends, especially in rural areas. We know that children and young people can benefit when police and mental health services work together. However, we need to better understand the full range of impacts of joint responses for young people and their families and how these impacts are generated. Joint emergency response is a complex intervention, and a realist synthesis was chosen as it can make sense of such interventions. Therefore, this realist synthesis aims to develop a programme theory of the underlying generative mechanisms by which, and contexts within which, emergency responders collaborate and co-respond to support young people experiencing a mental health crisis.

Methods and analysis: We will follow five steps to undertake the realist review: (1) Define the review scope, (2) develop initial programme theories, (3) conduct an evidence search, (4) select and appraise evidence, and (5) extract and synthesise data. Embase, CINAHL, Social Policy and Practice, MEDLINE, PsycINFO, and AMED databases will be searched up to June 2024, supplementing searches with citation tracking, grey literature, relevant NHS England guidance, and practitioner interpretation workshops. Data selection will be based on relevance and richness. Data will be extracted and synthesised iteratively, and causal links between contexts, mechanisms, and outcomes will be illuminated in the process. The results will be conducted and reported according to the Realist and Meta-narrative Evidence Syntheses: Evolving Standards (RAMESES) quality and publication standards.

Collaboration and dissemination: Findings will be disseminated to the research community through conference presentations and a peer-reviewed journal article. We will work with healthcare and police organisations, as well as professional and expert-by-experience stakeholder groups, including commissioners, to develop a strategy for far-reaching dissemination with impact to share findings across a range of audiences.

Discussion: This study will develop a programme theory regarding how emergency responders collaborate to support young people experiencing mental health crises. Findings will inform future practices, aiming to improve collaborative responses and outcomes across youth contexts.

Systematic review registration: PROSPERO CRD42024542081.