Chapter 026. Confusion and Delirium (Part 2)

EpidemiologyDelirium is a common disease, but its reported incidence has varied widely based on the criteria used to define the disorder. Estimates of delirium in hospitalized patients range from 14 to 56%, with higher rates reported for elderly patients and patients undergoing hip surgery. Older patients in the ICU have especially high rates of delirium ranging from 70 to 87%. The condition is not recognized in up to one-third of delirious inpatients, and the diagnosis is especially problematic in the ICU environment where cognitive dysfunction is often difficult to appreciate in the setting of serious systemic illness and sedation....
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Chapter 026. Confusion and Delirium (Part 2) Chapter 026. Confusion and Delirium (Part 2) Epidemiology Delirium is a common disease, but its reported incidence has varied widelybased on the criteria used to define the disorder. Estimates of delirium inhospitalized patients range from 14 to 56%, with higher rates reported for elderlypatients and patients undergoing hip surgery. Older patients in the ICU haveespecially high rates of delirium ranging from 70 to 87%. The condition is notrecognized in up to one-third of delirious inpatients, and the diagnosis is especiallyproblematic in the ICU environment where cognitive dysfunction is often difficultto appreciate in the setting of serious systemic illness and sedation. Delirium in theICU should be viewed as an important manifestation of organ dysfunction notunlike liver, kidney, or heart failure. Outside of the acute hospital setting, deliriumoccurs in nearly two-thirds of patients in nursing homes and in over 80% of thoseat the end of life. These estimates emphasize the remarkably high frequency of thiscognitive syndrome in older patients, a population expected to grow in theupcoming decade with the aging of the baby boom generation. In previous decades an episode of delirium was viewed as a transientcondition that carried a benign prognosis. Delirium has now been clearlyassociated with substantial morbidity and increased mortality, and is increasinglyrecognized as a sign of serious underlying illness. Recent estimates of in-hospitalmortality among delirious patients have ranged from 25 to 33%, a rate that issimilar to patients with sepsis. Patients with an in-hospital episode of deliriumhave a higher mortality in the months and years following their illness comparedwith age-matched nondelirious hospitalized patients. Delirious hospitalizedpatients have a longer length of stay, are more likely to be discharged to a nursinghome, and are more likely to experience subsequent episodes of delirium; as aresult, this condition has enormous economic implications. Pathogenesis The pathogenesis and anatomy of delirium are incompletely understood.The attentional deficit that serves as the neuropsychological hallmark of deliriumappears to have a diffuse localization with the brainstem, thalamus, prefrontalcortex, thalamus, and parietal lobes. Rarely, focal lesions such as ischemic strokeshave led to delirium in otherwise healthy persons; right parietal and medial dorsalthalamic lesions have been reported most commonly, stressing the relevance ofthese areas to delirium pathogenesis. In most cases, delirium results fromwidespread disturbances in cortical and subcortical regions, rather than a focalneuroanatomic cause. Electroencephalogram (EEG) data in persons with deliriumusually show symmetric slowing, a nonspecific finding supporting diffuse cerebraldysfunction. Deficiency of acetylcholine often plays a key role in delirium pathogenesis.Medications with anticholinergic properties can precipitate delirium in susceptibleindividuals, and therapies designed to boost cholinergic tone such ascholinesterase inhibitors have, in small trials, been shown to relieve symptoms ofdelirium. Dementia patients are susceptible to episodes of delirium, and those withAlzheimers pathology are known to have a chronic cholinergic deficiency statedue to degeneration of acetylcholine-producing neurons in the basal forebrain.Another common dementia associated with decreased acetylcholine levels,dementia with Lewy bodies, clinically mimics delirium in some patients. Otherneurotransmitters are also likely involved in this diffuse cerebral disorder. Forexample, increases in dopamine can also lead to delirium. Patients withParkinsons disease treated with dopaminergic medications can develop adelirious-like state that features visual hallucinations, fluctuations, and confusion.In contrast, reducing dopaminergic tone with dopamine antagonists such as typicaland atypical antipsychotic medications has long been recognized as effectivesymptomatic treatment in patients with delirium. Not all individuals exposed to the same insult will develop signs ofdelirium. A low dose of an anticholinergic medication may have no cognitiveeffects on a healthy young adult but may produce a florid delirium in an elderlyperson with known underlying dementia. However, an extremely high dose of the same anticholinergic medicationmay lead to delirium even in healthy young persons. This concept of deliriumdeveloping as the result of an insult in predisposed individuals is currently themost widely accepted pathogenic construct. Therefore, if a previously healthy individual with no known history ofcognitive illness develops delirium in the setting of ...