I may speak alike to you and my own conscious heart. —Percy Bysshe Shelley (1792–1822)
I. EVALUATION OF CONSCIOUSNESS
A. Two definitions of consciousness: intuitive and operational
Intuitively, we define consciousness as the awareness of self and environment. Or, more introspectively, we define consciousness as the awareness of our sensorium.
Operationally, physicians determine consciousness by practical steps.
B. Operations that establish consciousness
Physicians customarily employ inspection, verbal stimuli, and, if necessary, pain to determine the patient’s (Pt’s) awareness of self and environment.
Inspection: Does the Pt appear to adapt appropriately to the ongoing visual, auditory, and tactile stimuli of the ordinary environment?
Verbal stimuli: Does the Pt respond appropriately to inquiries and requests?
Pain: Does the Pt respond appropriately to pain?
For proof of conscious awareness, the Pt must have a receptor and its sensory pathway intact enough to receive stimuli and deliver those stimuli to the cerebrum. Then the Pt must have a motor pathway, neuromuscular junction, and an effector intact enough to produce a volitional behavior, verbal or nonverbal, that depends on consciousness. The examiner (Ex) cannot determine consciousness by clinical tests in a curarized Pt on the intensive care unit, a Pt with severe Guillain–Barré syndrome (GBS), or a Pt with bilateral hemiplegia, who lacks an intact effector system. See, however, the locked-in syndrome, pages 500–501.
C. Pathologic alterations in the level of consciousness
Disease may alter consciousness by causing various stages of delirium or coma.
Delirium (acute confusional state): Delirium means an acute, transient confusional state characterized by global impairment of the sensorium. The Pt shows disorientation, amnesia, misperceptions, hallucinations, (often vivid) delusions, brief attention span, disconnected thoughts, irrational or incoherent mutterings, and abnormally decreased or increased psychomotor activity (agitation). Rating scales enable a quantitative assessment (Trzepacz et al, 2002). The sleep and wake periods fail. Any such state of excessive neuronal activity may eventually cause tremors and convulsions (Diagnostic and Statistical Manual of Mental Disorders, 4th ed., 1994; Lipowski, 1989; Victor and Ropper, 2001). The delirious Pts then return to their previous mental state, or delirium may precede coma. Demented Pts may have periods of superimposed delirium. In aged and demented persons, delirium occurs most commonly at night. The causes of delirium include intracranial hemorrhage, infection, sleep deprivation, various drugs or withdrawal from drugs, toxic or metabolic states, and fever. Withdrawal from alcohol or other depressant drugs causes withdrawal delirium (delirium tremens), the classic example of delirium with excitement and often seizures (Chapter 11).
Coma (from the Greek word Koma meaning deep sleep) is sustained pathologic unconsciousness resulting from dysfunction of the ascending reticular activating system (ARAS) in the brainstem tegmentum or both cerebral hemispheres. Comatose patients cannot be aroused and their eyes remain closed (The Multi-Society Task Force on PVS, 1994).