Associations Between Inactivity and Cognitive Function in Older Intensive Care Unit Survivors

Critically ill older adults are profoundly inactive while in the intensive care unit (ICU), and this inactivity persists after discharge from the ICU. Older ICU survivors who were mechanically ventilated are at high risk for post-ICU cognitive impairment.

The present study examined the relationship between the ratio of daytime to nighttime activity and executive function in older ICU survivors.

This was a secondary analysis of pooled data from 2 primary studies of older adults who were functionally independent prior to hospitalization, mechanically ventilated while in ICU, and within 24 to 48 hours post-ICU discharge. Actigraphy recorded daytime activity (mean activity counts per minute, 6 am to 9:59 pm) and nighttime activity (mean activity counts per minute, 10 pm to 5:59 am). A daytime-to-nighttime activity ratio was calculated by dividing daytime activity by nighttime activity. The NIH Toolbox Dimensional Change Card Sort Test assessed cognitive flexibility (DCCST: fully corrected T score). Multivariate regression examined the association between the daytime-to-nighttime activity ratio and DCCST scores, adjusting for 2 covariates (age in years and NIH Toolbox Grip Strength fully corrected T score).

The mean daytime-to-nighttime activity ratio was 2.10 ± 1.17 (interquartile range, 1.42). Ratios for 6 participants (13.6%) were less than 1, revealing higher activity during nighttime hours rather than daytime hours. Higher daytime-to-nighttime ratios were associated with better DCCST scores (β = .364, P = .005).

The proportion of daytime activity versus nighttime activity was considerably low, indicating severe alterations in the rest/activity cycle. Higher daytime-to-nighttime activity ratios were associated with better executive function scores, suggesting that assessment of daytime activity could identify at-risk older ICU survivors during the early post-ICU transition period. Promotion of daytime activity and nighttime sleep may accelerate recovery and improve cognitive function.