Impaired Consciousness: General Considerations

Definition and EtiologyTop

Consciousness may be described as a state of being aware of self and aware of and responsive to one's surroundings. The level of consciousness depends on the activity of the reticular activating system (RAS) of the brain stem and cerebral cortex. Loss of consciousness may be caused by any pathologic state that interferes with the function of the RAS (eg, brainstem stroke), both cerebral cortices (eg, encephalitis), or both the RAS and cortices (eg, cardiac syncope). Between normal consciousness and complete loss of consciousness, states of partially preserved consciousness with limited ability to respond to external stimuli can be identified (Table 1). Also see Loss of Consciousness.

Diagnosis and TreatmentTop

Determination of the level of consciousness may be very difficult, for instance, in patients with aphasia, depression, or those treated with muscle relaxants. In such situations the neurologic assessment may be limited and interpretation of signs may not be accurate. Responses to the following stimuli are of diagnostic and prognostic importance in the assessment of a patient with a decreased level of consciousness: eye opening, verbal response, and motor response to pain stimuli. The Glasgow Coma Scale is most often used (Table 2). In the assessment take into account the best response. Repeat the examination periodically and monitor the dynamics of changes in the level of consciousness. A more detailed neurologic examination assessing brainstem functions (eg, pupillary function, extraocular movements, gag response) and cortical brain functions (eg, visual fields, language function) may identify the brain localization and possible etiology of the decreased level of consciousness.

Management: see Loss of Consciousness.

TablesTop