[Effect of epidural anesthesia on the fetus and the neonate]

The placental transfer of local anaesthetics (LA) depends on maternal factors (LA dosage, degree of protein binding, blood pH), placental factors (surface of placental exchange, placenta thickness) and fetal factors (maternal-fetal gradient of pH, fetal hepatic metabolism of the LA, redistribution of the cardiac output in case of fetal hypoxia). The assessment of effects of LA and epidural anaesthesia (EA) on the fetus is based on the monitoring of the fetal heart rate and the measurement of the fetal pH allowing to rapidly detect an acute fetal distress. Apgar score, analysis of blood gases in the umbilical artery and neurobehavioral tests (such as Brazelton test (NBAS). Early Neonatal Neurobehavioral Scale (ENNS) and Neurologic and Adaptative Capacity Score (NACS) allow an evaluation of the drugs effects on the neonate. Direct effects of LA: although a diminution of variability of the fetal heart rate has been reported little after the beginning of an EA using lidocaine, no significant modification of the fetal heart rate after EA using bupivacaine or lidocaine with epinephrine has been shown. Fetal neurological toxicity is rare and there are very little alterations of neurobehavioral scores after EA. Indirects effects on the uteroplacental blood flow (UBF): in high concentration, LA entail a vasoconstriction of uterine arteries but the main feared effect is maternal arterial hypotension that impedes directly the uteroplacental blood flow: fetal consequences depend on the importance and duration of the UBF decrease, the preliminary state of the utero-placental circulation and haemodynamic adaptative capacities of the fetus: when the former are exceeded, fetal hypoxia occurs and myocardial and brain oxygenation can be rapidly impaired if the haemodynamic state is not corrected.(ABSTRACT TRUNCATED AT 250 WORDS)