Participant retention in follow-up studies of intensive care unit survivors – A scoping review

Objective: To synthesize participant retention data and related reporting in studies evaluating post-hospital outcomes of survivors of critical illness after an intensive care unit (ICU) stay. Review method used: A synthesis of literature following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses Extension for Scoping Reviews checklist. Data sources: PubMed, EMBASE, PsycINFO, Cumulative Index of Nursing and Allied Health Literature, and the Cochrane Controlled Trials Registry. Hand searched reference lists and personal files of relevant narrative and systematic review articles. Review methods: Articles were screened by pairs of independent reviewers. Similarly, data were abstracted by pairs of data collectors, with conflicts resolved by consensus or by a third reviewer. Results: We included 243 publications, from 225 unique studies of 87,602 participants. Participant retention could not be calculated for any time-points in 13% of studies nor in 22% of all follow-up time-points. Retention ranged from 18–100%. When compared to follow-up before 1-month, retention at each later timepoint was not significantly different. Age and sex were not associated with retention and more recent studies had decreased retention (odds ratio: 0.94 [95% confidence interval: 0.92–0.96; p < 0.001]). Reporting of retention-related study methodology was inconsistent. Conclusion: Retention rate could not be calculated for 22% of study follow-up time-points, with retention at the remaining time-points generally being high (≥85%), but with high variability (18% – 100%). ICU survivorship research could be improved via: (i) more detailed guidance on reporting participant retention, and (ii) use of existing resources and best practices to facilitate better study design and to improve participant retention to preserve statistical power and reduce selection bias.