Oxytocin blood levels following different regimens of oxytocin administration in elective cesarean delivery

BACKGROUND: The use of oxytocin to prevent postpartum hemorrhage after elective cesarean delivery still remains empirical. The purpose of this study was to determine oxytocin serum levels following differents regimens of prophylactic oxytocin administration in pregnant women undergoing elective cesarean delivery. METHODS: 30 healthy pregnant patients were randomized to receive intravenous oxytocin, after clamping of the umbilical cord, into the following groups: G1 (n=9), 10 IU of oxytocin infused over 30 minutes (0.33 IU/min); G2 (n=11), 10 IU of oxytocin infused over 3 minutes and 45 seconds (2.67 IU/min) and G3 (n=10), 80 IU of oxytocin infused over 30 minutes (2.67 IU/min). Both patient and surgeon were blinded to the study group allocation. Uterine tone was assessed by palpation by the surgeon. Serum oxytocin concentration was determined by enzyme immunoassay (EIA) before anesthesia (T0) and at 5 (T5), 30 (T30) and 60 (T60) minutes following the start of oxytocin infusion. RESULTS: Serum oxytocin levels (mean ± standard error, ng/mL) were similar in the groups at T0 (0.062 ± 0.021, 0.039 ± 0.019 and 0.067 ± 0.041, respectively, P = 0.76), and T60 (0.648 ± 0.257, 0.356 ± 0.257 and 0.683 ± 0.257, respectively, P = 0.58). G3 presented higher serum oxytocin than G1 at T5 (3.651 ± 0.741 versus 0.709 ± 0.268, P = 0.01). At T30, serum oxytocin levels of G3 were higher than G1 (6.190 ± 1.195 versus 1.174 ± 0.375, P < 0.01) and also than G2 (6.190 ± 1.195 versus 0.411 ± 0.206, P < 0.01). Hemodynamic data were similar in all groups. Uterine tone was considered satisfactory in all intervals studied and no additional uterotonic agent was needed. CONCLUSION: We demonstrate serum oxytocin determinations by EIA in healthy pregnant women presented for elective cesarean delivery. Administering 80 IU in 30 min results in higher serum oxytocin levels at 5 and 30 min than the other two methods of oxytocin administration, but the concentrations did not differ at 60 min