Cerebral hemodynamic measurements in acute versus chronic asphyxia

In most reports of asphyxia in newborn infants, the occurrence, duration, frequency of episodes, or severity of the asphyxic insult is usually not known, and yet abnormal neurologic outcomes have been observed. The fetus has several innate characteristics that allow compensatory response to lack of oxygen over a reasonable duration of time; however, these inherent capabilities differ among individuals. Therefore, for a given asphyxic insult, the aftermath may be intact survival, some neurologic sequelae, or death. In an asphyxiated infant, an abnormal cerebral blood velocity flow pattern, especially if consistent with vasoparalysis, probably signals that an asphyxic or ischemic neuronal insult has occurred; the integrity of the neurons and their function are dependent on an appropriate uptake of oxygen and nutrients in the presence of adequate perfusion. Hemodynamic changes associated with acute asphyxia are different from those observed in chronic asphyxia. Based on information from experimental studies, less severe but prolonged asphyxia is associated with severer brain injury than when an insult is brief but severe. Thus, when asphyxia or ischemia is suspected based on obstetric monitoring, the fetus should be delivered under appropriate optimal conditions and resuscitative measures initiated if indicated. If all of ACOG's criteria for defining asphyxia are met, it could be assumed that a severe acute asphyxic insult or a repetitive insult has occurred. In cases where the only findings are abnormally low Apgar score and pH, the insult is most probably acute and brief. Thus, survival is likely not associated with any neurologic abnormality. With a likelihood that asphyxia has occurred, available therapeutic intervention should be initiated early, in the first 48 to 72 hours of life, without waiting for neurologic complications or multiorgan system failure to develop.