Fetal blood flow during intrathecal anaesthesia for elective caesarean section.

Fetal aortic and umbilical blood flows were studied in 15 mothers before and during spinal (intrathecal) anaesthesia for elective Caesarean section, using a method combining real-time ultrasonography and a pulsed Doppler technique. Spinal anaesthesia with 0.5% bupivacaine hydrochloride 2.5 ml in 8% glucose monohydrate solution was administered after preloading with 2 litre of lactated Ringer's solution. Simultaneously with the subarachnoid injection, an infusion i.v. of ephedrine 50 mg in 500 ml normal saline was initiated. Maternal heart rate and systolic arterial pressure remained stable during the spinal anaesthesia, but diastolic arterial pressure decreased (P less than 0.05). Fetal heart rate increased (P less than 0.05) 30 min after the introduction of the spinal anaesthesia, but blood flows in the fetal descending aorta and umbilical vein were unaffected. The pulsatility index of the fetal blood velocity decreased (P less than 0.05) both in the fetal aorta and in the umbilical artery 30 min after induction of the spinal anaesthesia, indicating a possible decrease in the placental vascular resistance. We conclude that, when normotension is maintained in the mother with a preload infusion and an infusion of ephedrine, spinal anaesthesia for Caesarean section has no harmful effect on the fetal circulation.