Cerebral Hypothermia in the Management of Hypoxic-Ischemic Encephalopathy

After completing this article, readers should be able to: 1. Describe the phases of hypoxic-ischemic encephalopathy (HIE). 2. Describe the role of hypothermia in experimental HIE. 3. Delineate the optimal level of cooling of the brain for treating HIE. 4. Describe the process of selective head cooling. Moderate-to-severe hypoxic-ischemic encephalopathy (HIE) continues to be an important cause of acute neurologic injury at birth, occurring at a rate of approximately 1 to 2 per 1,000 term live births. The possibility that hypothermia might be able to alleviate asphyxial brain injury is a “dream revisited.” Hypothermia initially was used in the therapy of infants following perinatal asphyxia in 1959, but this report and subsequent studies did not include control groups of infants treated at normal temperatures. Thus, neither the safety nor the efficacy of therapeutic hypothermia was proven. Recent studies have examined systematically the parameters required for successful neuronal rescue, including the delay in initiating cooling after the insult, its duration, and the depth of cooling attained. Such studies have confirmed that brief hypothermia during resuscitation has modest (and often transient) benefits, but moderate prolonged hypothermia still may be protective when delayed by many hours after severe hypoxia-ischemia (HI). Based on this work, a series of small trials have examined the feasibility of both whole body cooling and head cooling with mild systemic hypothermia in the severely asphyxiated newborn. The effects of neuroprotective hypothermia in experimental models is understood most easily in relationship to the timing of neuronal loss after HI. Considerable evidence from both clinical and experimental studies in the term fetus, newborn, and adults suggests that injury to the brain is not a single event occurring at, or just after the insult. Rather, it is an evolving process that leads to cell death well after the initial insult. Several phases are defined by key …