Gaining insight into study cohorts: challenges of follow-up research post intensive care

Van Gemert and colleagues recently published research titled “Getting valuable and valid insights in the life after ICU (…)”, in which they aimed to assess the external validity of their follow-up cohort of ICU survivors, the MONITOR-ICU [1]. The so-called MONITOR-ICU is a well-regarded multicenter consortium of six hospitals collecting patient-reported outcome measures (PROMs) for longitudinal follow-up studies of ICU survivors. Compared to a national insurance registry cohort of ICU admissions, substantial differences were observed in ICU mortality risk scores, the proportion of patients mechanically ventilated at admission, and the ICU (as well as hospital) length of stay of their follow-up ­cohort, although these differences were less pronounced in a ­homogeneous subgroup of cardiothoracic patients. Van Gemert and colleagues concluded that selection bias likely persists in participants of their follow-up cohort relative to the broader group of ICU admissions nationwide. They therefore caution that the findings may not be universally applicable, and lessons drawn from this study should be interpreted with this in mind. The question remains what the clinical implications are given the complexity of this follow-up research field.