- The neuroanatomy of coma can be divided into three major categories: diffuse brain dysfunction or bithalamic injury, primary brain stem disorders, and secondary brain stem compression from supratentorial and infratentorial mass lesions.
- Most cases of coma are due to metabolic disorders or exogenous drug intoxication.
- Patient evaluation must follow an orderly sequence, beginning with vital signs, general physical examination, and neurologic examination.
- The most important single sign distinguishing toxic-metabolic coma from primary brain disease is the presence of pupillary light responses.
- The neurologic examination of the patient in coma is brief and focuses on (1) level of consciousness, (2) pupils, (3) eye movements, (4) motor responses, and (5) respiratory pattern.
- Computed tomographic (CT) scanning of the brain is the most valuable acute test to rule out structural causes of coma.
- Hypoxic-ischemic encephalopathy after cardiopulmonary arrest or shock states may be ameliorated by aggressive measures to increase cerebral blood flow after resuscitation.
- Serial neurologic examination over the first 72 hours is most helpful to determine the prognosis for patients with atraumatic coma; for anoxic brain injury, failure to recover pupillary responses or corneal reflexes in the first 24 hours is a poor prognostic sign.
- As therapies aimed at cerebral resuscitation and preservation following acute injury are developed and proved efficacious, prior guidelines for determining prognosis will require redefinition and reconfirmation.
- The Uniform Determination of Death Act states that “an individual who has sustained either (1) irreversible cessation of circulatory and respiratory functions, or (2) irreversible cessation of all functions of the entire brain, including the brain stem, is dead."
- The determination of death by brain criteria is based on clinical examination, and in most cases does not require confirmatory tests. However, the cause of coma must be known, and the cause must be sufficient to explain irreversible cessation of whole brain function.
Consciousness is a difficult term to define, and even more complicating is the fact that many different meanings and classification systems exist for the various states of decreased level of consciousness, such as drowsiness, stupor, and coma. For practical reasons, however, in the evaluation of consciousness most clinicians give greater weight to the patient's responses and behavior than to what the patient says. Hence, consciousness can be defined in its simplest form as the patient's awareness of self and environment and the responsiveness to his or her needs and external stimulation. The level of consciousness used in clinical practice refers to the state of arousal and should be separated from the content of consciousness, which describes various forms of cognitive behaviors and thinking. An awake person is fully responsive (alert) to stimuli and is able to specify an awareness of self and environment.
Impaired consciousness is generally categorized by the level of responsiveness to external and internal stimuli (Table 67-1). Drowsiness (“lethargy") is a state of reduced physical and mental activity and a drowsy person can often not sustain wakefulness without external stimulation. It is similar in ...