Introduction An increasing number of teenagers and young adults (TYA) with chronic conditions and complex needs are transitioning from paediatric to adult services, including admission to intensive care units (ICUs). As these services are often ill-equipped to care for TYA, there is a risk of compromised care. Despite recent guidelines from the UK Paediatric Critical Care and Intensive Care Societies highlighting the importance and urgency of improving ICU transition, current recommendations are not evidence-based and established pathways for ICU transition remain limited.

Methods and analysis This mixed-methods research study aims to generate evidence to underpin national policy on transition from paediatric to adult ICUs that will improve clinical care and patient experience. To do this, we will: (1) link and analyse UK national data (years 2017–2024) on paediatric and adult ICU admissions, hospital inpatient, outpatient and emergency care visits and survival status, to determine the clinical characteristics and healthcare resource utilisation from teenage years to early adulthood of people admitted to an ICU as a young person (admission aged 14 and 15), and how these relate to ICU admissions after age 16; (2) conduct semistructured interviews, online forums and surveys with TYA patients, carers and health professionals to understand their experience of transition in ICU services; and (3) synthesise these strands of evidence and use a structured process of stakeholder engagement to propose potential targeted improvements as appropriate.

Ethics and dissemination This study was approved by the East of England - Cambridge South Research Ethics Committee on 1 August 2024 (research ethics committee number 24/EE/0108), and the Health Research Authority Confidentiality Advisory Group (CAG) on 7 October 2024 (CAG number 24/CAG/0068). Study results will be actively disseminated through peer-reviewed journals, conference presentations and accessible lay texts and graphic summaries for the use of charities and patients including those with learning disabilities and neurodevelopmental disorders.