A mixed methods systematic review of the impact of paediatric mental health liaison services on children and young people's mental and physical health, stakeholder experience, and service-level outcomes.

Children and young people (CYP) with physical and mental health needs commonly present to acute hospitals. Although evidence shows liaison services providing mental health assessment and intervention to adult acute hospitals users improve outcomes, there is no evidence review for Paediatric Mental Health Liaison (PMHL). A mixed-methods, integrative, systematic review, using Joanna Briggs Institute (JBI) guidance, was conducted to identify evidence for PMHL service impacts on stakeholder experience and health and service level outcomes in the acute hospital setting.Keyword searches of relevant databases including Medline and PsycINFO plus citation searching identified 10,111 records; 415 papers were eligible for full-text screening. 53 papers describing mental health services/interventions provided to CYP aged 0-25 in acute hospital settings and reporting data on health and service-level outcomes, or stakeholder experiences were included. Service description, outcomes, and stakeholder experience data were extracted from included papers. Quantitative findings were 'qualitized' and analysed thematically. Quality appraisal used JBI tools.Studies were mostly cross-sectional (n = 27) or quasi-experimental (n = 13), from the US (n = 28) or England (n = 11). Service descriptions ranged from multidisciplinary teams covering entire hospitals to single mental health professionals integrated into one physical health department. Presence of PMHL services improve length of stay and healthcare costs/utilization, but evidence has methodological limitations. Evidence for PMHL services' impact on health outcomes is also positive but weak. PMHL services are valued by physical healthcare staff and parents/carers, but CYP views were underrepresented. Further work needs to establish outcomes important to CYP and families.Prospero Registration Number: CRD42022383611.