Consciousness is usually described as having two components:
arousal and awareness. Many terms are used to describe the continuum
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. The comatose patient appears
asleep and does not respond to 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. 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.
The neurologic examination includes assessment of level of consciousness,
brainstem reflexes, and motor activity. The Glasgow Coma Scale
(GCS) (Table 36–1) was designed
to assess level of consciousness in patients with head injury. A patient
with a GCS of 8 or lower is generally considered to be comatose.
Brainstem reflexes, including pupillary response to light, corneal
reflexes, oculocephalic reflex (doll’s eyes), vestibuloocular
reflex (cold calorics), breathing patterns, and cough and gag reflexes,
are further used to accurately describe the level of consciousness
and localize the level of brainstem dysfunction. Motor responses
may be described as spontaneous or induced by noxious stimuli, purposeful
or nonpurposeful, unilateral or bilateral, and upper or lower extremity.
The patient may display withdrawal from a stimulus, abnormal flexion
(decorticate rigidity), abnormal extension (decerebrate rigidity),
or absence of motor activity.
Table 36–1. Glasgow Coma Scale. |Favorite Table|Download (.pdf)
Table 36–1. Glasgow Coma Scale.
|Best motor response:|
|Abnormal flexion posturing||3|
The differential diagnosis of altered states of consciousness is
broad (Table 36–2), and while the
etiology may be obvious, as in trauma, a history, physical examination, laboratory
studies, and imaging studies may be required to establish a diagnosis.
Metabolic etiologies (eg, sodium or glucose abnormalities) and pharmacologic
causes (eg, sedatives or illicit drugs) should be excluded. Onset
and progression of symptoms may provide important clues; for example, neoplasms
often present with a progressive course, while vascular occlusions
often present with abrupt changes. Associated symptoms and conditions
such as recent fevers or a history of diabetes may also aid in diagnosis.
Table 36–2. Etiology of Altered State of Consciousness.