Some idea of the dimensions of the problem of coma can be obtained from published statistics. Eighty years ago, in two large municipal hospitals, it was estimated that 3 percent of all admissions to the emergency wards were for diseases that had caused coma. Alcoholism, cerebral trauma, and cerebrovascular diseases were the most common, accounting for 82 percent of the comatose patients admitted to the Boston City Hospital (Solomon and Aring). Epilepsy, drug intoxication, diabetes, and severe infections were the other major causes for admission. It is perhaps surprising to learn that contemporary figures from large city hospitals differ only slightly, with intoxication, stroke, and cranial trauma standing as the “big three” of coma-producing conditions. For example, in the series collected by Plum and Posner (Table 16-1) a majority was the result of exogenous (drug overdose) and endogenous (metabolic) intoxications and hypoxia, 25 percent of cases proved to have cerebrovascular disease, and intracranial masses—such as tumors, abscesses, and hemorrhages—made up about one-third of cases. Subarachnoid hemorrhage, meningitis, and encephalitis accounted for another 5 percent. Common in some series, although obvious and often transient, is coma that follows seizures or resuscitation from cardiac arrest.
The terms consciousness, confusion, stupor, unconsciousness, and coma have been endowed with so many different meanings that it is almost impossible to avoid ambiguity in their usage. They are not strictly medical terms but are also literary, philosophic, and psychologic ones. The word consciousness is the most ambiguous of all. William James remarked that everyone knows what consciousness is until they attempt to define it. To the psychologist, consciousness denotes a state of continuous awareness of one’s self and environment, essentially self-consciousness. Knowledge of self includes all “feelings, attitudes and emotions, impulses, volitions, and the active or striving aspects of conduct”; in short, a near continuous self-awareness of a person’s mental functioning, particularly of cognitive processes. These can be judged only by the individual’s verbal account of his introspections and indirectly, by his actions.
Physicians, aspiring to be more practical and objective, give greater credence to the patient’s behavior and reactions to stimuli than to what the patient reports. In this way the term consciousness is used in its broadest operational meaning—namely, the state of awareness of self and environment, and normal responsiveness to external stimulation and inner need.
This narrow definition has an advantage in that unconsciousness has the opposite meaning: a state of unawareness of self and environment or a suspension of those mental activities by which people are made aware of themselves and their environment, coupled with an overtly observable diminished responsiveness to environmental stimuli. The last of these qualities, arousal, or the level of consciousness, refers to the appearance of being awake as displayed by the facial muscles, eye opening, fixity of gaze, and body posture, that is, wakefulness.
A distinction is made in medicine between the level of consciousness and the content of consciousness, the latter reflecting the quality and coherence of thought and behavior. For neurological purposes, the loss of normal arousal is the dramatic aspect of disordered consciousness and the one identified by laypersons and physicians as being the central feature of coma. However, the state of confusion, or delirium is more ubiquitous and caused by a large variety endogenous and exogenous disorders, and the bizarre and illogical qualities of psychosis are a component of the study of psychiatric disease.