Michael G. Shashaty and Paul N. Lanken

Definition

Altered mental status (also referred to as “a change in mental status [MS]” or “delta MS”) is a vague but commonly used term that is applied to both alterations in level of consciousness and alterations in cognitive function (cognition, attention, awareness). Level of consciousness can be quickly characterized according to the AVPU scale (Box 36.1). This simplification of the Glasgow Coma Scale is easy to remember and document. Additionally, the ordered continuum allows for tracking of changes in level of consciousness, whereas nonspecific terms such as stuporous or lethargic do not conform to a clear hierarchy. After establishing level of consciousness, cognitive function is assessed to further detail the nature of the disturbance. A commonly used alternative scale to follow level of sedation and agitation in ICU patients is the Richmond Agitation-Sedation Scale or RASS (which is described in more detail in Chapters 5 and 37).

Changes in mental status can arise by two mechanisms: (1) disruption of function in the brain stem reticular activating system or, more commonly, (2) through processes affecting both cerebral hemispheres. Severe dysfunction produces coma, defined as an unresponsive and unarousable state. Less severe dysfunction produces an acute confusional state in which the patient may be sleepy, disoriented, or inattentive but responds to some stimuli in a purposeful manner. The term delirium is more specific than just being confused or disoriented. Delirium is defined as an acute change or fluctuation in mental status combined with inattention and either an altered level of consciousness or disorganized thinking. Delirium is common in ICU patients, with an incidence of 50% or higher (see Chapter 37 for details about diagnosis and management of delirium).

An acute change in mental status is distinct from dementia, aphasia, or psychiatric decompensation. An acute confusional state lasts for hours to days; in contrast, dementia has a much longer time course and is associated with fewer fluctuations in attention and perception. Aphasia can be detected by careful examination of language function. Psychiatric conditions that can mimic an acute confusional state include schizophrenia, depression, mania, autism, and dissociative states. Seizures can also produce a confusional state during the period of actual epileptic discharge or for minutes to hours during the immediate postictal period. Because details of a patient’s baseline and medical history may not be immediately available, however, it is useful to consider dementia, aphasia, and psychiatric decompensation in the initial approach to mental status change.