The Out-of-Hospital Cardiac Arrest Outcomes (OHCAO) project is the UK’s national registry for out-of-hospital cardiac arrest. Led by the Warwick Clinical Trials Unit at Warwick Medical School and funded by the British Heart Foundation and Resuscitation Council UK, it is the most comprehensive source of data on cardiac arrest epidemiology and outcomes in the UK — and one of the most important tools we have for understanding why survival rates vary so dramatically between regions and services.
What Is OHCAO?
OHCAO is a prospective observational study collecting data on all out-of-hospital cardiac arrests attended by NHS ambulance services across the UK where resuscitation is attempted. It standardises how cardiac arrest data is collected and reported across services — aligning with international Utstein recommendations — and builds an anonymised research database that enables benchmarking, quality improvement, and academic research.
The registry collects data on system characteristics, EMS dispatch, patient characteristics, and process variables. Key outcome measures include return of spontaneous circulation (ROSC) and survival at 30 days and beyond. The data has revealed significant variation in survival rates between ambulance services — variation that cannot be explained by case mix alone — and has driven targeted quality improvement work across the NHS.
Why It Matters for Survivors
For cardiac arrest survivors and co-survivors, OHCAO represents something important: the systematic attempt to understand not just who survives, but why — and to use that understanding to save more lives and improve the care of those who do survive. Historically, cardiac arrest data was collected by ambulance services for audit purposes only, with no national picture and no ability to compare outcomes or share learning. OHCAO changed that.
The registry has published annual epidemiology reports since its establishment, covering survival rates, bystander CPR rates, defibrillation rates, and other key indicators across English ambulance services. In 2024 it published the first ever national data on paediatric out-of-hospital cardiac arrest — a landmark that will shape clinical practice and training for years to come.
SCA UK and OHCAO
SCA UK has a longstanding relationship with the Warwick Clinical Trials Unit. Our members represent a critical and often overlooked constituency in cardiac arrest research — the survivors themselves — and our contribution to OHCAO-linked work reflects our broader commitment to ensuring that the patient voice is embedded in research design, not added as an afterthought. This is the essence of Patient and Public Involvement and Engagement (PPIE), and it is work we take seriously.
Further Information
The OHCAO project website, including published epidemiology reports, research projects, and data sharing information, is available at warwick.ac.uk/ohcao.
See also our pages on Cardiac Arrest Research and Cardiac Arrest Registries for related resources.