Effects of intravenous infusion rate of oxytocin on thoracic epidural pressure in parturients undregoing elective cesarean section

Abstract

The effects of intravenous oxytocin on thoracic epidural pressure during cesarean section were studied in 90 parturients (American Society of Anesthesiologists physical atatus class I or II) after obtaining informed consent. The subjects were randomized to either a control (control group; n=30), bolus (bolus group; n=30) or drip treatment group (drip group; n=30). The subjects were anesthetized with 11 approximately 12 mg of intrathecal isobaric bupivacaine (0.5%). An epidural catheter placed at Th 11/12 was connected to a pressure transducer to continuously monitor thoracic epidural pressure. Ten units of oxytocin were administered over 30 seconds in the bolus group and over 5 minutes in the drip group after fetus delivery. We analyzed epidural pressure, mean blood pressure, and heart rate, until 5 minutes after fetus delivery. Epidural pressures in both bolus and drip groups increased after fetus delivery compared with control group (P<0.0001). Epidural pressure immediately after placental delivery in the bolus group was higher than in the control group (p<0.0001) and epidural pressure at 5 minutes after fetus delivery in the drip group was higher than in the control group (p=0.0452). There were no significant differences in changes in blood pressure and heart rate among the three groups. We concluded that the increase in epidural pressure with intravenous administration of oxytocin 10 units over 5 minutes was lower than with intravenous administration of oxytocin 10 units over 30 seconds after fetus delivery.