Process Evaluation of an Ambulance-Delivered Early Intensive Blood Pressure-Lowering Stroke Trial: Design, Rationale, and Reflection.

Introduction: The fourth INTEnsive ambulance-delivered blood pressure Reduction in hyper-ACute stroke Trial (INTERACT4) is a large-scale, multicenter, prospective, randomized, open-label, blinded endpoint assessment trial, initiated in an ambulance in China, aiming at evaluating the effectiveness and safety of prehospital blood pressure (BP) lowering in patients with suspected acute stroke and elevated BP. A prespecified process evaluation is intended to explore the implementation of the trial intervention, provide support to interpret the trial outcomes and put forward suggestions to scale up the intervention in broader settings in the future.

Methods: This process evaluation is a mixed-methods design, and follows the Normalization Process Theory (NPT) and the UK Medical Research Council (UK MRC) guidance. Fidelity, reach, acceptability, appropriateness, adoption, sustainability, and relevant contextual factors and mechanisms affecting the implementation of prehospital early intensive BP-lowering treatment will be analyzed. Semi-structured interviews with ambulance staff, ward and emergency department clinicians, and nurses are undertaken to explore perceptions of the intervention, contextual factors, and potential suggestions for future implementation in practice. Data from observational records, surveys, conventional monitoring data, on-site records, and case report forms will be analyzed to understand background care and context.

Conclusion: The process evaluation of INTERACT4 will provide insights for the implementation of prehospital early intensive BP-lowering intervention in different health systems and help better explain the trial results for further scale up.