Delirium and its motoric subtypes: a study of 614 critically ill patients.

OBJECTIVES: To describe the motoric subtypes of delirium in critically ill patients and compare patients aged 65 and older with a younger cohort.
DESIGN: Prospective cohort study.
SETTING: The medical intensive care unit (MICU) of a tertiary care academic medical center. PARTICIPANTS: Six hundred fourteen MICU patients admitted during a process improvement initiative to monitor levels of sedation and delirium. MEASUREMENTS: MICU nursing staff assessed delirium and level of consciousness in all MICU patients at least once per 12-hour shift using the Confusion Assessment Method for the Intensive Care Unit and the Richmond Agitation-Sedation Scale. Delirium episodes were categorized as hypoactive, hyperactive, and mixed type.
RESULTS: Delirium was detected in 112 of 156 (71.8%) subjects aged 65 and older and 263 of 458 (57.4%) subjects younger than 65. Mixed type was most common (54.9%), followed by hypoactive delirium (43.5%) and purely hyperactive delirium (1.6%). Patients aged 65 and older experienced hypoactive delirium at a greater rate than younger patients (41.0% vs 21.6%, P<.001) and never experienced hyperactive delirium. Older age was strongly and independently associated with hypoactive delirium (adjusted odds ratio=3.0, 95% confidence interval=1.7-5.3), compared with no delirium in a model that adjusted for other important determinants of delirium including severity of illness, sedative medication use, and ventilation status.
CONCLUSION: Older age is a strong predictor of hypoactive delirium in MICU patients, and this motoric subtype of delirium may be missed in the absence of active monitoring.