Evaluating the implementation and impact of a new model of care for integrating children and young people's acute mental healthcare in a paediatric setting: a protocol for a realist, mixed-methods approach.

INTRODUCTION: The mental health of children and young people in the UK has been declining and has continued to worsen throughout the pandemic, leading to an increase in mental health-related emergencies. In response, the Best for You programme was developed as a new service designed to integrate mental healthcare for children and young people between acute hospital and community services. The programme is comprised of four new services: a rapid assessment young people's centre with dual-trained staff, a co-located day service offering family-based care,a digital hub, designed to integrate with the fourth element of the model, namely community support and mental health services. This evaluation protocol aims to assess the development, implementation and outcomes of the Best for You programme and develops a scalable model that could be implemented in other parts of the National Health Service (NHS). METHODS AND ANALYSIS: This mixed-methods realist evaluation aims to delineate the components of the system to assess their interdependent relationships within a wider context. Data collection will include interviews, participant observations, focus groups and the collection of local quantitative healthcare data. The research will be conducted across four phases. Phase 1-captures the development of the underlying programme theory. Phase 2-a process evaluation testing the programme theory. Phase 3- an outcome and economic evaluation. Phase 4-consolidation of learning from phases 1-3 to identify barriers, facilitators and wider contextual factors that have shaped implementation drawing on the Consolidated Framework for Implementation Research. ETHICS AND DISSEMINATION: Ethical approval for the evaluation was received from the NHS local ethics committee. Embedded within the evaluation is a formative review to feedback and share learning with stakeholders to scale-up the programme. Findings from this study will be disseminated in peer-reviewed journals as well as presentations to be useful to service user organisations and networks.