Intensive care unit delirium is an independent predictor of longer hospital stay: a prospective analysis of 261 non-ventilated patients

Abstract

Introduction: Delirium occurs in most ventilated patients and is independently associated with more deaths, longer stay, and higher cost. Guidelines recommend monitoring of delirium in all intensive care unit (ICU) patients, though few data exist in non-ventilated patients. The study objective was to determine the relationship between delirium and outcomes among non-ventilated ICU patients.

Method: A prospective cohort investigation of 261 consecutively admitted medical ICU patients not requiring invasive mechanical ventilation during hospitalization at a tertiary-care, university-based hospital between February 2002 and January 2003. ICU nursing staff assessed delirium and level of consciousness at least twice per day using the Confusion Assessment Method for the ICU (CAM-ICU) and Richmond Agitation-Sedation Scale (RASS). Cox regression with time-varying covariates was used to determine the independent relationship between delirium and clinical outcomes.

Results: Of 261 patients, 125 (48%) experienced at least one episode of delirium. Patients who experienced delirium were older (mean +/- SD: 56 +/- 18 versus 49 +/- 17 years; p = 0.002) and more severely ill as measured by Acute Physiology and Chronic Health Evaluation II (APACHE II) scores (median 15, interquartile range (IQR) 10-21 versus 11, IQR 6-16; p < 0.001) compared to their non-delirious counterparts. Patients who experienced delirium had a 29% greater risk of remaining in the ICU on any given day (compared to patients who never developed delirium) even after adjusting for age, gender, race, Charlson co-morbidity score, APACHE II score, and coma (hazard ratio (HR) 1.29; 95% confidence interval (CI) 0.98-1.69, p = 0.07). Similarly, patients who experienced delirium had a 41% greater risk of remaining in the hospital after adjusting for the same covariates (HR 1.41; 95% CI 1.05-1.89, p = 0.023). Hospital mortality was higher among patients who developed delirium (24/125, 19%) versus patients who never developed delirium (8/135, 6%), p = 0.002; however, time to in-hospital death was not significant the adjusted (HR 1.27; 95% CI 0.55-2.98, p = 0.58).

Conclusion: Delirium occurred in nearly half of the non-ventilated ICU patients in this cohort. Even after adjustment for relevant covariates, delirium was found to be an independent predictor of longer hospital stay.

Figure 1

Delirium versus ICU length of stay. This Kaplan-Meier plot shows the relationship between delirium and length of stay in the ICU by classification of Ever Delirium versus Never Delirium (p = 0.004, univariate analysis).

Figure 2

Delirium versus hospital length of stay. This Kaplan-Meier plot shows the relationship between delirium and hospital length of stay by classification of Ever Delirium versus Never Delirium (p < 0.001, univariate analysis).

Figure 3

Delirium versus in-hospital mortality. This Kaplan-Meier plot shows the relationship between delirium and in-hospital mortality by classification of Ever Delirium versus Never Delirium (p = 0.11, univariate analysis).