Cerebral protection means prevention of cerebral neuronal damage. Severe brain damage extinguishes the very "human" functions such as speech, consciousness, intellectual capacity, and emotional integrity. Many pathologic conditions may inflict
injuries to the brain, therefore the protection and salvage of cerebral neuronal function must be the top priorities in the care of
critically ill patients. Brain tissue has unusually high energy requirements, its stores of energy metabolites are small and, as a result, the brain is totally dependent on a continuous supply of substrates and
oxygen, via the circulation. In complete global
ischemia (
cardiac arrest) reperfusion is characterized by an immediate
reactive hyperemia followed within 20-30 min by a delayed hypoperfusion state. It has been postulated that the latter contributes to the ultimate neurologic outcome. In focal
ischemia (
stroke) the primary focus of
necrosis is encircled by an area (ischemic penumbra) that is underperfused and contains neurotoxic substances such as
free radicals,
prostaglandins,
calcium, and excitatory
neurotransmitters. The variety of therapeutic effort that have addressed the question of protecting the brain reflects their limited success. 1)
Barbiturates. After an initial enthusiastic endorsement by many clinicians and years of vigorous controversy, it can now be unequivocally stated that there is no place for
barbiturate therapy following
resuscitation from
cardiac arrest. One presumed explanation for this negative statement is that cerebral metabolic suppression by
barbiturates (and other
anesthetics) is impossible in the absence of an active EEG. Conversely, in the event of incomplete
ischemia EEG activity in usually present (albeit altered) and metabolic suppression and hence possibly protection can be induced with
barbiturates. Indeed, most of the animal studies led to a number of recommendations for
barbiturate therapy in man for incomplete
ischemia. 2)
Isoflurane. From a cerebral metabolic standpoint, exposure to
isoflurane at concentration of 2 MAC is credited with providing the same potential for protection as high dose
barbiturate (isoelectric EEG). A possible major difference between
barbiturates and
isoflurane is the modest cerebral vasodilation induced by the latter while
barbiturates are associated with decreased CBF. This suggests that in focal
ischemia isoflurane may elicit an intracerebral steal. 3)
Calcium entry blockers. Some
calcium entry blockers with the distinctive feature of acting preferably on cerebral as opposed to systemic vascular smooth muscles may exert beneficial effects during or after
brain ischemia. Two such drugs which have shown promise are
nimodipine and
lidoflazine. In animal and human studies
nimodipine has been reported to improve the neurologic outcome of both the
cerebral vasospasm and the postischemic hypoperfusion state.(ABSTRACT TRUNCATED AT 400 WORDS)