Delirium Overview
We hope that this website will serve as a valuable resource for both medical and lay readers interested in learning about delirium in critically ill patients, neurological monitoring instruments for use in the hospital setting, newly recommended patient-oriented (goal-directed) sedation practices, and the under-recognized problem of long-term cognitive impairment following critical illness. In addition to overview narratives, the website provides many training materials and resources for well-validated neurological monitoring instruments including the Confusion Assessment Method for the ICU (CAM-ICU) and the Richmond Agitation-Sedation Scale (RASS), the CAM-ICU Training Manual PDF, frequently asked questions (FAQs) PDF, a printable Pocket Card for medical personnel use, instructional videos, and a list of links to selected references from the peer reviewed literature. We believe that increased awareness and monitoring of delirium and improvements in the delivery of potent psychoactive medications including analgesics and sedatives will lead to better care of critically ill patients and ultimately improve patient outcomes.
Terminology: Over 25 different terms have been used to describe the spectrum of cognitive impairment in the ICU including: ICU psychosis, ICU syndrome, acute confusional state, septic encephalopathy and acute brain failure. The Diagnostic and Statistical Manual of Mental Disorders (DSM IV) officially defines delirium as a disturbance of consciousness with inattention accompanied by a change in cognition or perceptual disturbance that develops over a short period of time (hours to days) and fluctuates over time.
The three motoric subtypes of delirium are hyperactive, hypoactive, and mixed. Medical and nursing literature often refers to patients with hyperactive delirium as having ICU psychosis. The neurology literature generally uses the term “delirium” to refer almost exclusively to hyperactive patients and “acute encephalopathy” as a synonym for hypoactive delirium. We recognize that patients in the ICU develop the spectrum of 3 delirious states (hyper, hypo, and mixed). For general purposes within this website, we will use the term “delirium” to indicate the spectrum of these states and will make distinctions between these motoric subtypes whenever possible with regard to etiology, clinical outcome, and treatment.
Etiology: Most patients with delirium in the ICU likely have multiple causes, though these causes are often very difficult to determine with clinical precision. In fact, in our past work, we have determined that on average, ICU patients have greater than 10 risk factors for delirium which places them at a very high risk for this complication. The exact pathophysiological mechanisms involved in the development and progression of delirium are a point of controversy. However, these mechanisms are thought to be related both to (a) anatomic deficits and (b) imbalances in the neurotransmitters which modulate the control of cognitive function, behavior and mood. We will elaborate very briefly on these two categories of mechanism.
(a) Anatomic Deficits: Higher cortical areas of the brain such as the prefrontal and non-dominant posterior parietal regions are implicated by CT/MRI or SPECT scans in delirium. Other regions touted as important in such studies include the anterior thalamus, basal ganglia, and the temporal-occipital cortex. A nice review of this work is found in Trzepacz P, Sem Clin Neuropsychiatry 2000;5: 132-48.
(b) Neurotransmitter Imbalance: Derangements in levels of serotonin, acetylcholine deficiency and dopamine excess (to name 3) are thought to contribute to delirium, but there are many other neurotransmitters that may be involved. Such derangements could be secondary to a number of causal factors that include reduction in cerebral metabolism, primary intracranial disease, systemic diseases, secondary infection of the brain, exogenous toxic agents, withdrawal from substances of abuse such as alcohol or sedative-hypnotics agents, hypoxemia and metabolic disturbances, and the administration of psychoactive medications such as benzodiazepines and narcotics. A recent study from our group (Pandharipande P et al, Anesthesiology. 2006;104:21-26) documented, for example, that three important risk factors for transitioning to delirium were patient age (FIGURE 2), severity of illness (FIGURE 3), and the administered dose of the sedative lorazepam (FIGURE 1). It is important to emphasize that these data should not indicate a need to avoid lorazepam, as it has an important role in the management of ICU patients, and it is also true that other sedative and analgesic medications are deliriogenic as well. We would emphasize, however, that avoiding the use of any more of these medications than is absolutely necessary is likely an area of focus that may reduce either the onset or duration of delirium. This is a point of ongoing study in the medical field.
Prevalence and Clinical Relevance: Critically ill patients are at great risk for the development of delirium in the ICU. With more than 8 out of 10 ventilated patients experiencing delirium, this is one of the most frequent forms of organ dysfunction experienced by critically ill patients. Despite this prevalence, delirium (usually in the hypoactive state) remains unrecognized in 66% to 84% of patients whether they be in the ICU, hospital ward, or emergency department. Delirium in the non-ICU setting has repeatedly been associated with prolonged hospital stay, medical complications that can increase mortality, greater dependency of care on discharge, and higher nursing home disposition rates. In medical and coronary ICU patients, delirium has been reported to be an independent predictor of prolonged ICU and hospital lengths of stay, as well as a higher 6 month mortality rates. Importantly these findings were present even after adjusting for age, gender, race and severity of illness. Delirium may also predispose ICU survivors to prolonged neuropsychological deficits.
Delirium Monitoring: The Confusion Assessment Method for the ICU (CAM-ICU) is a valid and reliable serial assessment tool for monitoring delirium in both ventilated and nonventilated ICU patients. The CAM-ICU is easy to use and takes less than 2 minutes to complete. (For more information see the links to the left) Inattention, which can be readily assessed using the CAM-ICU, is the hallmark and pivotal feature of delirium. Remember, delirium is an acquired brain disorder, and should be thought of as a form of organ dysfunction much like low-grade shock or hypoxemia are considered organ dysfunction for the cardiovascular or pulmonary systems. Inattention is a core symptom by which to recognize this form of organ dysfunction in an arousable patient.
Vanderbilt University Medical Center
Veterans Affairs TN Valley Geriatric Research Education and Clinical Center (GRECC)