The plight of Terry Schiavo, the young woman at the center of the much-publicized legal battle in Florida, illustrates the devastation of the chronic vegetative state following anoxic injury (one that deprives the brain of oxygen). Adults who suffer cardiac arrest and oxygen deprivation to the brain leading to a persistent vegetative state that lasts beyond three months have essentially no statistical chance of further recovery. This grim prognosis rests on a convergence of evidence from studying outcomes in large numbers of patients; in addition, it is supported by evidence of diffuse neuronal damage in the cerebral cortex and other higher brain regions in such an injury. Measurement of patients’ brain activity further demonstrates the loss of cerebral function, with the resting metabolic activity in chronic vegetative states following anoxic injuries averaging less than half the level in normal brains. Structural imaging studies in such cases typically reveal widespread neuron loss and cerebral atrophy similar in extent to that observed in the end-stages of Alzheimer’s disease. Brain electrical activity is grossly disturbed, if evident at all.
Patients in this state may live for years, occasionally smiling, shedding a tear, or briefly appearing to fix their gaze on something. These reflex behaviors in the chronic phase of PVS do not reflect awareness or the potential for further recovery. Many of these facial displays are organized by intrinsic circuits of the brainstem and do not depend on the integrity of higher centers of the brain, including the cortex and thalamus, which are overwhelmingly damaged in patients who chronically remain in a vegetative state. In rare instances, islands of cerebral activity do remain on levels higher than the brainstem, producing fragments of behavior that are not responses to anything in the environment. The presence of these fragmentary behaviors, unfortunately, does not improve the prognosis or suggest greater potential for recovery in patients remaining in vegetative states beyond the three-month period following an anoxic injury. Thus, each patient’s examination should be considered in the overall context of the history of their illness, along with the results of structural brain imaging and studies of function.
To the untrained observer, the simple appearance of wakefulness is difficult to dissociate from an inference of awareness, especially if this appearance is accompanied by brief, out-of-context, reflexive behaviors that also can be misinterpreted. This emotionally charged situation dictates extraordinarily careful and repeated efforts to reduce the uncertainty in making the diagnosis. In the Schiavo case, many qualified experts have testified that repeated examinations of the patient have revealed a vegetative state, that structural imaging has confirmed the neuron loss and widespread atrophy, and that repeated testing has documented the absence of brain electrical activity. In the aggregate, this evidence is as unequivocal, and lacking in reasons for hope, as any obtainable in these circumstances.