Clinical Syndromes

Neurologic syndromes after an episode of anoxia vary greatly, depending upon the length of anoxia. Patients successfully and promptly resuscitated from out-of-hospital CA are a minority (5-20%), but they generally have good neurologic outcomes and quality of life (8). Brief episodes of anoxia are generally well tolerated, although some patients may develop an amnestic syndrome with severe anterograde amnesia, presumably due to the vulnerability of hippocampal regions involved in memory (9). Longer episodes of anoxia may result in a watershed pattern of cerebral ischemia (10). These patients are typically in a coma for 12 hr or more. Watershed infarctions can cause quadriparesis, with weakness primarily in the proximal arm and leg, typically sparing the hands and feet ("man-in-the-barrel" syndrome). Finally, rare cases of spinal cord stroke occur due to hypotension, in the absence of cerebral injury (11). Plum et al. reported a series of patients who had delayed neurologic deterioration after they awoke from anoxic coma (12). Patients appeared to show good recovery, lasting one to several weeks, but then had recurrent neurologic deterioration, sometimes even to coma and death. Pathologically, the brain shows extensive demyelination, although the pathogenesis remains unclear.

Patients with more prolonged anoxia suffer diffuse cerebral injury, with variable recovery ranging from encephalopathy to persistent coma. Many of these patients develop seizures and/or myoclonus within the first 24 hr of CA. In one report, 17% of patients developed myoclonic status epilepticus, a condition associated with uniformly poor outcome (13 ).

Selective injury can occur to the large pyramidal cells of layers III and V of the cerebral cortex (laminar necrosis), while the brain stem and spinal cord are preserved (14). The clinical status of patients with this type of injury progresses to a vegetative state, in which the eyes are open but the patient lacks interaction and apparent awareness. Vegetative patients are considered to be in a "persistent" vegetative state if no change in status occurs for 1 month or more, and in a "permanent" vegetative state if no change occurs after 3 months (15). Although laminar necrosis is a common pathologic finding in vegetative patients, it is not the only one that can cause the condition (14,16). The chance of late recovery from a vegetative state is poor. A review of studies found that, after 1 year, 15% of patients in a vegetative state awakened, 32% remained vegetative, and 53% died (4,5). Among the 15% of patients who awakened (n = 25), only one had a good neurologic recovery.

Because of this poor prognosis, the ability to predict early on the patients who will die or remain vegetative and to distinguish them from patients who will eventually awaken and possibly have reasonable medical recovery is highly desirable. Such information would be of great value to families of patients trying to decide on continuing life-sustaining treatments.

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