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Coma is the severest form of impaired consciousness. Coma is a state of apparent sleep that does not respond to a stimulus of any type. Less severe disturbances of consciousness include stupor, which is a state of apparent sleep that will respond to vigorous physical stimulation, and somnolence, which is a state of apparent sleep that will respond to a verbal command. Confusion is often associated with impaired consciousness. An acute confessional state is known as a delirium. If a delirium manifests with thoughts that contain fixed false beliefs, then these are described as delusions. Delirium is usually reversible and can be either hyperactive or hypoactive. This distinction is important to the anesthesiologist as hyperactive delirium with delusions and hallucinations are more often secondary to medications, while hypoactive delirium is often secondary to an organic cause such as hypoglycemia, increased intracranial pressure, or infection. If a confusional state is of a chronic nature, it is considered dementia.
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Forty percent of comatose states are drug related, 25% are secondary anoxia often associated with cardiac arrest, 20% are related to stroke, and the last 15% are secondary to other causes, including head injury, shock, hypoglycemia, and hypothermia.
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Consciousness is described as having two elements: arousal and content. The scoring systems for coma assess arousal not content. Patients in a persistent vegetative state are unaware, but in contrast to coma, patients in a persistent vegetative state are wakeful. They are described as having a “wakeful unconscious state.”
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Level of consciousness can be evaluated using the Glasgow Coma Scale (GCS). The Glasgow Coma Scale is recommended for patients over 4 years old. Best motor, verbal, and eye opening are evaluated on a scale of 3–15 (Table 32-1). Eye opening, facial grimace to pain, and a purposeful withdrawal of a limb from a noxious stimulus indicate that consciousness is not sufficiently impaired and can be followed. If motor responses are symmetric to pain, especially with up going toes on Babinski exam, then a focal hemispheric lesion is likely. The GCS does not strictly follow the definition of coma; however, 90% of patients with a score equal or less than 8 will meet the strict definition of coma. The children’s coma score table can be used for children less than 4 years old (Table 32-2).
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