The prognostic importance of subsyndromal delirium is unknown.
To test whether duration of subsyndromal delirium is independently associated with institutionalization.
The Confusion Assessment Method for the Intensive Care Unit (CAM-ICU) was used twice daily to assess for subsyndromal delirium in patients with respiratory failure or shock. Delirium was considered present if the assessment was positive. Subsyndromal delirium was considered present if the assessment was negative but the patient exhibited any CAM-ICU features. Multivariable regression was used to determine the association between duration of subsyndromal delirium and institutionalization, adjusting for age, education, baseline cognition and disability, comorbidities, severity of illness, delirium, coma, sepsis, and doses of sedatives and opiates.
Subsyndromal delirium, lasting a median of 3 days, developed in 702 of 821 patients (86%). After adjusting for covariates, duration of subsyndromal delirium was an independent predictor of increased odds of institutionalization (P = .007). This association was greatest in patients with less delirium (P for interaction = .01). Specifically, of patients who were never delirious, those with 5 days of subsyndromal delirium (upper interquartile range [IQR]) were 4.2 times more likely to be institutionalized than those with 1.5 days of subsyndromal delirium (lower IQR).
Subsyndromal delirium occurred in most critically ill patients, and its duration was an independent predictor of institutionalization. Routine monitoring of all delirium symptoms may enable detection of full and subsyndromal forms of delirium.