CHAPTER 82

#### INTRODUCTION

Patients in the intensive care unit (ICU) who experience delirium are exhibiting an under-recognized form of organ dysfunction. Delirium is extremely common in ICU patients as factors such as comorbidity, the acute critical illness itself, and iatrogenesis intersect to create a high-risk setting for delirium. This neurologic complication is often hazardous, being associated with death, prolonged hospital stays, and long-term cognitive impairment and institutionalization. Neurologic dysfunction compromises patients’ ability to be removed from mechanical ventilation or to fully recover and regain independence. Unfortunately, health care providers in the ICU are unaware of delirium in many circumstances, especially those in which the patient's delirium is manifesting predominantly as the hypoactive (quiet) subtype rather than the hyperactive (agitated) subtype. Despite being often overlooked clinically, ICU delirium has increasingly been the subject of research during the past decade, which has brought to light the scope of the problem in critically ill patients and provided clinicians with tools for routinely monitoring delirium at the bedside. This chapter reviews the definition and salient features of delirium, its primary risk factors, including drugs associated with the development of delirium, proposed pathophysiologic mechanisms, validated methods for bedside delirium assessment, and nonpharmacologic and pharmacologic strategies for delirium management.

#### DEFINITION AND TERMINOLOGY

The American Psychological Association's (APA) Diagnostic and Statistical Manual of Mental Disorders (DSM)-IV describes delirium as a disturbance in consciousness and cognition that develops over a short period of time (eg, hours to days) and tends to fluctuate during the course of the day.1 Specifically, there are four criteria required to diagnose delirium1:

1. Disturbance of consciousness, with reduced awareness of the environment and impaired ability to focus, sustain or shift attention.

2. Altered cognition (eg, memory impairment, disorientation, or language disturbance) or the development of a perceptual disturbance (eg, delusion, hallucination, or illusion) that is not better accounted for by preexisting or evolving dementia.

3. Disturbance develops over a short period of time (usually hours to days) and tends to fluctuate during the course of the day.

4. Evidence of an etiological cause, which the DSM-IV uses to classify delirium as Delirium Due to a General Medical Condition, Substance-Induced Delirium, Delirium Due to Multiple Etiologies, or Delirium Not Otherwise Specified.

Historically, two words were used to describe acutely confused patients. The Roman word delirium referred to an agitated and confused person (ie, hyperactive delirium). The Greek word lethargus was used to describe a quietly confused person (ie, hypoactive delirium). ICU patients commonly demonstrate both subtypes of delirium as they progress through different stages of their illness and therapy. In both subtypes, the patient's brain is not functioning normally. It therefore makes sense that the original derivation of delirium comes from the Latin word deliria, which literally means to “be out of your furrow.” For greater clarity and to avoid misuse of terms such as dementia and delirium, Table 82-1 lists basic definitions and ...

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