The incidence of delirium in psychiatric inpatient units

To estimate prospectively the incidence of delirium in psychiatric inpatients and to identify risk factors for delirium in this population.

The subjects were nondelirious patients newly admitted to the Calgary General Hospital. The Delirium Symptom Interview (DSI), the Confusion Assessment Method (CAM), and the Mini-Mental State Examination (MMSE) were used to identify incident cases of delirium. In order to evaluate the potential impact of selection bias, we conducted a supplementary analysis using record linkage to an electronic administrative data base with coverage of the target population.

Of 420 admissions to the hospital, 401 subjects provided informed consent and were not delirious at the time of admission. There were 9 incident cases of delirium. The cumulative incidence rate was, therefore, 2.14 per 100 admissions. The record linkage analysis did not uncover evidence of selection bias. Delirium was associated with a significantly increased length of stay in hospital.

Delirium is an uncommon incident event in the psychiatric inpatient population. The incidence rate reported here may be useful as a benchmark for the identification of excessive rates in other inpatient settings. Since delirium is sometimes related to modifiable therapeutic factors, an excessive rate should prompt a search for its causes.