Circadian health after critical COVID-19 illness: a 24-month follow-up study

Abstract

A substantial proportion of critical illness survivors experience circadian disruptions following intensive care unit (ICU) discharge. However, the long-term circadian function in these patients remains poorly understood. This study aimed to characterize the circadian health of ICU survivors over a 24 month follow-up. Patients admitted to the ICU due to SARS-CoV-2 infection were recruited, and rest–activity rhythms (7-day actigraphy), mental health (Hospital Anxiety and Depression Scale), quality of life (12-item Short Form Survey), and respiratory function (spirometry) were assessed at short-term follow-up and at 24 months. The main analysis included 52 patients (65.4% male) with a mean (SD) age of 59.2 (8.27) years. The cohort showed a mean (95% CI) increase in circadian function index (CFI) of 0.06 (0.03–0.09). Participants were categorized into two groups: those without and those with a clinically meaningful improvement, defined as a ≥ 10% increase in CFI. Improvements in CFI correlated with changes in DLCO (rrm = 0.31; 0.04–0.54) and FEV 1 (0.43; 0.17–0.63). Longer duration of invasive mechanical ventilation was associated with lower CFI at 24 months (effect size = –0.338; –0.637 to –0.038). These findings indicate that while some survivors show circadian recovery over 24 months, others exhibit persistent alterations, supporting circadian-focused strategies in post-ICU rehabilitation.