Failure of two different doses of ondansetron to prevent maternal hypotension in spinal anesthesia with ropivacaine 0.75% for cesarean section; a randomized, double blind trial.

Abstract

Introduction: Ondansetron, a selective 5-hydroxytryptamine 3 (5-HT3) receptor antagonist, commonly used as an antiemetic has been proven in recent studies to be effective for the prevention of spinal-induced hypotension for elective cesarean section.   Methods: One hundred and thirty-eight healthy primigravida parturients scheduled for elective cesarean section were randomly assigned to three groups. Participants in the ONDA4, ONDA8, and CONTROL groups received 4 mg of ondansetron, 8 mg of ondansetron and normal saline respectively, 10 minutes before spinal anesthesia. Spinal anesthesia was performed at L3-L4 interspinous space, with 1.7 ml ropivacaine 0.75% and 15 mcg of fentanyl, via a 27 G pencil point needle. Blood pressure and heart rate were recorded upon arrival at the operating room, after preloading with 500 ml of 6% hydroxyethylstarch, at the time of spinal injection, and at one-minute intervals for 10 minutes thereafter. Blood pressure and heart rate values, total phenylephrine (mcg) or/and ephedrine (mg) doses, the incidence of maternal nausea/vomiting/shivering, umbilical artery pH and Apgar scores at 1 and 5 min were recorded. Time for the sensory block to reach T4 and regress to T7 dermatome, and the time for the motor block to reach Bromage scale 3 and to regress to Bromage scale 1, were also noted.     Results: There were no differences between groups in hemodynamic parameters or doses of vasoactive agents used, sensory or motor block characteristics, incidence of nausea/vomiting, umbilical artery pH or Apgar scores of the neonates.   Conclusion: Our results failed to demonstrate the significance of ondansetron in preventing maternal hypotension following spinal anesthesia for cesarian section.