Skip to Main Content

We have a new app!

Take the Access library with you wherever you go—easy access to books, videos, images, podcasts, personalized features, and more.

Download the Access App here: iOS and Android


Alterations of consciousness and the related conditions of delirium, acute confusional state, and acute encephalopathy are among the most common mental disorders encountered in either surgical or medical patients. The prevalence of altered mental status in hospitalized patients is high, with reported rates up to 50%. These conditions are associated with increased mortality rates ranging from 10% to 65%, and excess annual health care expenditures in the billions. Given the high incidence of altered mental states, at least a basic understanding of the pathophysiology, diagnosis, and management of common etiologies is warranted for all medical practitioners.


Consciousness is generally defined as the subjective experience of the environment and the self. It is comprised of two components: arousal, which is the state of wakefulness, and awareness, which is the state of phenomenal perception. This distinction is useful, since the two processes are dissociable. For example, a vegetative state is characterized by a patient that is awake (ie, the cortex is aroused), but not necessarily aware.

Arousal is generated by activity of the ascending reticular activating system, which is composed of neurons within the central mesencephalic brainstem, the lateral hypothalamus, and portions of the thalamus. Widespread projections of these nuclei synapse on neurons in the cerebral cortex and generate an arousal response. Arousal responses define the level of consciousness (eg, being awake vs. asleep vs. comatose). Awareness is thought to be generated through networks involving the thalamus and association cortices of the frontal, parietal, temporal, and occipital lobes. Processes related to awareness define the content of consciousness (eg, seeing a blue circle vs. a red triangle).

Many terms are used to describe the levels of consciousness ranging from alert to comatose. The alert patient is awake and immediately responsive to all stimuli. Stupor is a condition in which the patient is less alert but still responds with stimulation. An obtunded patient appears to be asleep much of the time but still responds to noxious stimuli. A vegetative state is a state of arousal without awareness in which the patient may open his or her eyes, track objects, chew, and swallow, but not respond to auditory stimuli or appear to sense pain (although pain processing is now known to occur in the vegetative state). The comatose patient appears asleep and does not respond to stimuli. Often, terms used to describe states of consciousness lack consistent definitions, and a clear description of a patient’s state of arousal and awareness results in more precise communication.


In general, altered states of consciousness can arise from physiologic, pharmacologic, and pathologic causes. Before addressing pathologic causes (which can have structural or nonstructural etiologies), physiologic perturbations such as hypoglycemia, hypoxia, hypercarbia, hyponatremia, and hypothermia should be addressed. Pharmacologic etiologies, such as acute intoxication, overdose, and residual anesthesia ...

Pop-up div Successfully Displayed

This div only appears when the trigger link is hovered over. Otherwise it is hidden from view.