Risk factors, coma, and consequences of intensive care unit delirium

Objectives

To establish risk factors for the development of delirium in an ICU, to determine the effect of ICU delirium screened with the Intensive Care Delirium Checklist on mortality and ICU and hospital lengths of stay, and to clarify the comorbidity and clinical effect of coma on the incidence of delirium and on outcome.

Design and setting

Prospective study in a 16-bed university hospital medical/surgical ICU.

Patients

A total of 820 consecutive patients admitted to the ICU for more than 24 hours.

Interventions

Fifteen covariates, including medical history, severity of illness on admission (APACHE II), laboratory values, and medications were prospectively recorded for a total of 4707 patient-days (mean = 5.7 ± 7 days). All patients were screened a minimum of three times daily. Follow-up to hospital discharge was provided in all patients. Hospital length of stay, and hospital mortality, were compared between delirium and non-delirium patients. Comatose patients were arbitrarily separated into those whose coma was transient (< 5 days) or lasting (5 days or more).

Results

Hypertensive patients, smokers, and alcoholics were more likely to develop delirium (odds ratios of 1.68, 1.56, and 1.77, respectively). Delirium was independently associated with severity of illness on admission; each additional point on the APACHE score was associated with a 4% increase in risk of delirium. Coma, regardless of its duration, increased the incidence of delirium (51% and 54% for shorter and longer duration of coma, vs 20% in patients with no coma, P < 0.05). The development of delirium was not associated with benzodiazepine or opiate use. Patients who developed ICU delirium were more likely to die in hospital (47% compared with 37% in patients without delirium, P < 0.005), and had a significantly longer length of stay (18 days compared with 13 days, P < 0.005). Mortality was proportional to severity of illness on admission (APACHE), presence of diabetes, total length of hospital stay and delirium occurrence.

Conclusion

Delirium risk factors include tobacco and alcohol use, a history of hypertension, and preceding ICU coma but not ICU benzodiazepine or opiate use. Significant mortality and longer hospital stay are attributable to this morbid condition. Awareness of patients at risk may lead to better recognition and earlier intervention.