Understanding implementation patterns of the FICUS family support intervention: a matrixed multiple case study across Swiss adult intensive care units

Abstract Background Variations in implementation success across sites are common when introducing complex health interventions; however, such variations are rarely examined systematically, particularly for family-focused interventions in intensive care units (ICUs). As part of a clinical trial, a nurse-led, multicomponent family support intervention (FSI) was implemented in eight Swiss ICUs using a tailored implementation approach. Understanding site-specific differences and contextual determinants that influence implementation success is essential to inform future scale-up and sustainability of the FSI across diverse ICU settings. Methods A Matrixed Multiple Case Study (MMCS) design was used to examine multilevel implementation determinants across ICUs with 228 ICU staff members. Implementation success was assessed using three global items from the Normalization Measure Development questionnaire (Global-NoMAD). Data were collected at four time points over an 25-month period (03/2022–04/2024). Prior to the implementation, a contextual analysis assessed baseline determinants (T0). During active implementation, a process evaluation examined implementation progress (T1–T2), followed by a summative evaluation to assess overall implementation success (T3). MMCS steps 1–4 were conducted retrospectively to define the research focus, identify key determinants, and prepare site-specific data, while steps 5–9 were applied prospectively to construct the cross-case matrix, compare implementation patterns and to identify contextual and phase-related configurations. Results Implementation success ranged from 60 to 80% on the Global-NoMAD scale (range: 0-100%) across ICUs. One ICU met the predefined threshold for high implementation success (≥ 75%), while the remaining seven achieved moderate success (56–74%). Implementation was facilitated by low culture stress, organizational readiness, adequate infrastructure and resources, motivated and skilled family nurses, high acceptability of the FSI, and external implementation support. In contrast, trial-related processes (e.g. recruiting family members) were consistently identified as barriers. No specific configurations of contextual determinants were identified that systematically explained differences in implementation success across ICUs. Conclusions Implementation success of the FSI across ICUs was moderate to high. Contextual determinants were largely similar across sites. No distinct determinant configurations explaining implementation success were identified, likely due to shared challenges, the small number of sites and the limited sample size.