Update on Definitions, Interpretation, and Research Guidelines

Umbilical cord blood gas and acid-base assessment are themost objective determinations of the fetal metabolic condition at the momentof birth. Moderate and severe newborn encephalopathy, respiratory compli-cations, and composite complication scores increase with an umbilicalarterial base deficit of 12–16 mmol/L. Moderate or severe newborn compli-cations occur in 10% of neonates who have this level of acidemia and therate increases to 40% in neonates who have an umbilical arterial base deficitgreater than 16 mmol/L at birth. Immediately after the delivery of the neonate,a segment of umbilical cord should be double-clamped, divided, and placedon the delivery table. Physicians should attempt to obtain venous and arte-rial cord blood samples in circumstances of cesarean delivery for fetal com-promise, low 5-minute Apgar score, severe growth restriction, abnormal fetalheart rate tracing, maternal thyroid disease, intrapartum fever, or multifetalgestation. Laboratory research demonstrates a complex relationship between fetal(antepartum and intrapartum) asphyxia, newborn asphyxia, and possibleresulting brain damage. The degree, duration, and nature of the asphyxicinsult are modulated by the quality of the cardiovascular compensatoryresponse. A task force set up by the World Federation of Neurology Groupdefined asphyxia as a condition of impaired blood gas exchange, leading, ifit persists, to progressive hypoxemia and hypercapnia (1). This is a precisedefinition of asphyxia as it may affect the fetus and neonate. In the AmericanCollege of Obstetricians and Gynecologists’ Task Force on NeonatalEncephalopathy and Cerebral Palsy report, asphyxia is defined as: . . . [a] clinical situation of damaging acidemia, hypoxia, and metabolic acidosis. This definition, although traditional, is not specific to cause. A more complete definition of birth asphyxia includes a requirement for a recognizable sentinel event capable of interrupting oxygen supply to the fetus or infant. This definition fails to include conditions that are not readily recognized clinically, such as occult abruption, but is probably correct in a majority of cases. (2) Asphyxia may occur in a transient fashion that, although of physiologicinterest, has no pathologic sequelae. Significant fetal exposure to asphyxiaFOR CLASSROOM USE ONLY