Background

In the intensive care unit (ICU), inactivity is common, contributing to ICU-acquired weakness and poor outcomes. Actigraphy may be useful for measuring activity in the ICU.

Objectives

To use actigraphy to characterize inactivity and activity in critically ill patients.

Methods

This prospective observational study involved 48-h wrist actigraphy in medical ICU (MICU) patients, with activity data captured across 30-s epochs. Inactivity (zero-activity epochs) and activity (levels of non-zero activity) were summarized across key patient (e.g., age) and clinical (e.g., mechanical ventilation status) variables, and compared using multivariable regression.

Results

Overall, 189,595 30-s epochs were collected in 34 MICU patients. Zero-activity (inactivity) comprised 122,865 (65%) of epochs; these epochs were 24% and 13% more prevalent, respectively, in patients receiving mechanical ventilation (versus none, p < 0.001) and in the highest (versus lowest) organ failure score tertile (p = 0.03). Ambulatory (versus non-ambulatory) patients exhibited more non-zero activity (35 more movements per epoch, p < 0.001), while those in the highest (versus lowest) organ failure score tertile exhibited less activity (22 fewer movements per epoch, p = 0.03). Significant inactivity/activity differences were not observed when evaluated based on age, sedation, or restraint status.

Conclusions

Actigraphy demonstrated that MICU patients are profoundly inactive, including those who are young, non-sedated and non-restrained. Hence, ICU-specific, non-patient-related factors may contribute to inactivity, an issue requiring further investigation.

Circadian alignment of rest-activity rhythms is an essential biological process that may be vulnerable to misalignment in critically ill patients. We evaluated circadian rest-activity rhythms in critically ill patients and their association with baseline (e.g. age) and clinical (e.g. mechanical ventilation status) variables, along with intensive care unit light-dark cycles. Using wrist actigraphy, we collected 48-hr activity and light exposure data from critically ill patients in a tertiary care medical intensive care unit. We evaluated circadian rest-activity rhythms using COSINOR and non-parametric circadian rhythm analysis models, and stratified these data across baseline and clinical variables. We used linear regression to evaluate the association of circadian rest-activity and light-dark exposure rhythms. In COSINOR and non-parametric circadian rhythm analysis analyses, the 34 medical intensive care unit patients completing 48-hr actigraphy recordings exhibited mean MESOR (mean activity levels of a fitted curve) and amplitudes of 0.50 ± 0.32 and 0.20 ± 0.19 movements per 30-s epoch, with high interdaily variability. Patients who were older, mechanically ventilated, sedated, restrained and with higher organ failure scores tended to exhibit greater circadian rest-activity misalignment, with three of 34 (9%) patients exhibiting no circadian rhythmicity. Circadian light-dark exposure misalignment was observed as well and was associated with rest-activity misalignment (p = 0.03). Critically ill patients in our MICU experienced profound circadian rest-activity misalignment, with mostly weak or absent rhythms, along with circadian light-dark exposure misalignment. Potentially modifiable factors contributing to rest-activity misalignment (i.e. mechanical ventilation, restraints, low daytime light levels) highlight possible targets for future improvement efforts.