Delirium in the intensive care unit (ICU) represents an acute form of organ dysfunction, which manifests as a rapidly developing disturbance of both consciousness and cognition that tends to fluctuate throughout the course of a day.1 The American Psychiatric Association’s (APA) Diagnostic and Statistical Manual of Mental Disorders (DSM)-IV defines four key features of delirium: 1) Disturbance of consciousness with reduced awareness of the environment and impaired ability to focus, sustain or shift attention; 2) Altered cognition (e.g., impaired memory, language disturbance or disorientation) or the development of a perceptual disturbance (e.g., hallucinations, delusions, or illusions) that is not better accounted for by preexisting or evolving dementia; 3) Disturbance develops over a short period of time (hours to days) and tends to fluctuate during the course of the day; and 4) Evidence of an etiologic cause (i.e., delirium due to general medical condition, substance induced delirium, delirium due to multiple etiologies, or delirium not otherwise specified).1
Delirium is common in the ICU, affecting 60–80% of mechanically ventilated patients and 20–50% of non-mechanically ventilated patients.2–8 Its presence heralds both short- and long-term adverse outcomes. In the hospital, delirious patients are at increased risk for prolonged mechanical ventilation, catheter removal, self-extubation and need for physical restraints.3,9,10 In addition, delirium predisposes patients to longer hospital stays, with greater healthcare costs, increased risk of death during the hospitalization and increased odds of institutionalization following discharge.10–15 Even after hospital discharge, the amount of time a patient was delirious in the ICU predicts long-term cognitive impairment, physical disability and death up to a year later.12,16–20
Given the common occurrence of delirium and the adverse outcomes associated with its presence, preventing delirium in the ICU is a key piece to enhancing the quality of care in ICUs worldwide. But, before considering preventive strategies, one must first ask whether delirium in the ICU can be prevented from developing in the first place? Though some ICU patients develop delirium due to a single, preventable risk factor—and thus recognition and avoidance or minimization of this risk factor may effectively prevent the patient from developing delirium—delirium more often occurs when a vulnerable patient (i.e., having multiple predisposing risk factors) encounters a large insult or insults (i.e., develops a precipitating risk factor).21 Frequently the insult causing delirium is the critical illness leading to ICU admission, such that a large number of patients are delirious prior to arrival in the ICU. Indeed, delirium commonly occurs in conjunction with other acute organ failures such as respiratory failure, shock, and/or renal failure. By the time of ICU admission, the ‘horse is out of the barn’ for many patients, because the syndrome has already developed and therefore cannot be prevented. Even in these patients, though, “preventive” strategies may be of benefit via their effect on duration of delirium. Multiple studies have found that the number of days an ICU patient is delirious is associated with numerous adverse outcomes, including cognitive impairment, physical disability and death in the year following a critical illness.
Thus, we review herein strategies to prevent not only the development of delirium in critically ill patients but also to prevent the persistence of delirium in the ICU, which may be a more attainable goal. Many of these strategies are part of the recently described “ABCDE” approach to ICU care, which clinicians can use to address modifiable risk factors associated with delirium and improve outcomes for their patients.