AIM: The aim of the study was to evaluate intervention fidelity of nurses' delivery of the RAPIT recovery program for postintensive care patients.

BACKGROUND: Interventions addressing patient problems after intensive care lack description of the process of delivery and the evidence of their effectiveness. This is needed to understand how these interventions work.

DESIGN: Multistage intervention framework in a mixed-methods design. Intervention fidelity strategies were assessed for intervention design, training, delivery, receipt, and enactment with quantitative and qualitative methods inspired by the Medical Research Council and the National Institutes of Health Fidelity Framework.

METHODS: Data collection was embedded in a multicenter randomized controlled trial to explore intervention fidelity of a recovery program (December 2012-February 2017). Ten Danish intensive care units participated in the RAPIT-trial including 386 patients and 27 nurses. Quantitative data covered training and delivery. Qualitative data explored design, quality of delivery, receipt, and enactment seen from nurses' and patients' perspectives. Data were analysed statistically and by systematic deductive-inductive thematic analysis.

FINDINGS: A framework for participatory enactment of a complex intervention was developed and demonstrated delivery with high consistent fidelity across sites. Low delivery doses and variations were related to the program, patient, provider nurses and context.

CONCLUSION: Our study provides insight into the process of intervention fidelity of a nurse-led postintensive care recovery program and potentially enables professionals to understand key factors in cross-site implementation. Although we demonstrate consistent delivery and variations suggest that some patients may benefit more than others.