Serum oxytocin concentrations in elective caesarean delivery: a randomized comparison of three infusion regimens.

The aim of this study was to determine serum oxytocin concentrations following different regimens of prophylactic oxytocin administration in women undergoing elective caesarean delivery. Thirty healthy pregnant patients were randomized, after clamping of the umbilical cord, to receive intravenous oxytocin in one of the following groups: G1 (n=9), 10 IU of oxytocin infused over 30 min (0.33 IU/min); G2 (n=11), 10 IU of oxytocin infused over 3 min and 45 s (2.67 IU/min); and G3 (n=10), 80 IU of oxytocin infused over 30 min (2.67 IU/min). Both patient and surgeon were blinded to allocation. Uterine tone was assessed by surgical palpation. Serum oxytocin concentration was determined by enzyme immunoassay before anaesthesia (T0) and at 5 (T5), 30 (T30) and 60 (T60) min after the start of oxytocin infusion. Serum oxytocin concentrations (mean±standard error, ng/mL) were not significantly different in the groups at T0 (0.06±0.02, 0.04±0.02 and 0.07±0.04, respectively, P=0.76), and T60 (0.65±0.26, 0.36±0.26 and 0.69±0.26, respectively, P=0.58). G3 showed higher concentrations than G1 at T5 (3.65±0.74 versus 0.71±0.27, P=0.01) and at T30 (6.19±1.19 versus 1.17±0.37, P<0.01), and were higher than G2 at T30 (6.19±1.19 versus 0.41±0.2, P<0.01). Haemodynamic data and uterine tone were considered satisfactory and similar in all groups. No additional uterotonic agents were needed. Serum oxytocin measurements made using enzyme immunoassay in healthy pregnant women undergoing elective caesarean delivery showed that administration of 80 IU oxytocin over 30 min resulted in higher serum oxytocin levels after 5 and 30 min than the two other regimens. The concentrations did not differ between groups at 60 min.