Impaired Consciousness: General Considerations

How to Cite This Chapter: Oczkowski W, Zwolińska G, Jankowski M, Szułdrzyński K. Impaired Consciousness: General Considerations. McMaster Textbook of Internal Medicine. Kraków: Medycyna Praktyczna. Accessed December 06, 2022.
Last Updated: November 4, 2021
Last Reviewed: November 4, 2021
Chapter Information

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 1.3-1). 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 1.3-2). 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.



Table 1.3-1. Disturbances of consciousness

Descriptive term



Patients seem fully awake but their thoughts and actions are incoherent and chaotic; likely disoriented to time or place; exclude aphasia, which may mimic confusion


Sudden onset and fluctuating symptoms that feature inattention or easy distractibility and disorganized thinking, or fluctuations in consciousness from a hypervigilant state to lethargic

Lethargy (excessive drowsiness)

Patients wake in response to verbal stimuli, provide verbal responses, and make voluntary movements


Patients wake after a strong (vigorous, repeated) stimulation, show no or minimal response to verbal commands


No response even to strong pain stimuli; reflexive movements can occur

Table 1.3-2. Glasgow Coma Scale

Type of reaction



Eye opening



To verbal command


To pain stimuli


No response


Verbal response

Normal, patient is fully oriented


Responds but is disoriented


Uses inappropriate words


Inarticulate sounds


No response


Motor response

To verbal command


Can locate pain stimuli


Undirected and nonpurposeful movements of the limbs


Abnormal flexion posturing of arms, legs in extension (decorticate)


Abnormal extension posturing of arms, legs in extension (decerebrate)


No response


Adapted from Lancet. 1974;2(7872):81-4.

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