Delirium in the cardiovascular ICU: exploring modifiable risk factors

Abstract

Objective: Delirium, an acute organ dysfunction, is common among critically ill patients leading to significant morbidity and mortality; its epidemiology in a mixed cardiology and cardiac surgery ICU is not well established. We sought to determine the prevalence and risk factors for delirium among cardiac surgery ICU patients.

Design: Prospective observational study.

Setting: Twenty-seven-bed medical-surgical cardiac surgery ICU.

Patients: Two hundred consecutive patients with an expected cardiac surgery ICU length of stay >24 hrs.

Interventions: None.

Measurements: Baseline demographic data and daily assessments for delirium using the validated and reliable Confusion Assessment Method for the ICU were recorded, and quantitative tracking of delirium risk factors were conducted. Separate analyses studied the role of admission risk factors for occurrence of delirium during the cardiac surgery ICU stay and identified daily occurring risk factors for the development of delirium on a subsequent cardiac surgery ICU day.

Main results: Prevalence of delirium was 26%, similar among cardiology and cardiac surgical patients. Nearly all (92%) exhibited the hypoactive subtype of delirium. Benzodiazepine use at admission was independently predictive of a three-fold increased risk of delirium (odds ratio 3.1 [1, 9.4], p = 0.04) during the cardiac surgery ICU stay. Of the daily occurring risk factors, patients who received benzodiazepines (2.6 [1.2, 5.7], p = 0.02) or had restraints or devices that precluded mobilization (2.9 [1.3, 6.5], p < 0.01) were more likely to have delirium the following day. Hemodynamic status was not associated with delirium.

Conclusions: Delirium occurred in one in four patients in the cardiac surgery ICU and was predominately hypoactive in subtype. Chemical restraints via use of benzodiazepines or the use of physical restraints/restraining devices predisposed patients to a greater risk of delirium, pointing to areas of quality improvement that would be new to the vast majority of cardiac surgery ICUs.

Figures

Figure 1. A Two-Step Process of Delirium Assessment

Using the Richmond Agitation-Sedation Scale (RASS), the level of sedation and arousal is assessed (Step 1). If the patient can respond to verbal stimulation (RASS level ≥ −3), then delirium assessment with the Confusion Assessment Method for the Intensive Care Unit (CAM-ICU) is performed (Step 2).

Figure 2. Duration of Delirium in the Cardiovascular Intensive Care Unit

A histogram displaying the duration of delirium in CVICU patients. The X axis represents the days of delirium, and the Y axis the number of patients.