Most research in this field has focused on finding oxytocin doses for initiating uterine contractions. Only limited data are available regarding the optimal rate of oxytocin infusion to maintain adequate uterine tone. This randomised, double blind study included 120 healthy term pregnant patients with uncomplicated, singleton pregnancy undergoing elective caesarean section under spinal anaesthesia. Following an initial 1 IU bolus, the patients received oxytocin infusion at 1.25 IU/hour (group 1.25), 2.5 IU/hour (group 2.5) or 5.0 IU/hour (group 5) for four hours. Uterine tone was assessed as adequate or inadequate at various intervals. If found inadequate, additional uterotonics were administered. Estimated blood loss was mean (standard deviation) 499 (172) ml, 454 (117) ml and 402 (151) ml in groups 1.25, 2.5 and 5, respectively (P value groups 1.25 versus 5 = 0.012). Oxytocin infusion at 5 IU/hour resulted in a significantly lower incidence of minor postpartum haemorrhage, defined as blood loss greater than 500 ml, than 1.25 IU/hour (P = 0.009). No patient had major/severe haemorrhage (>1000 ml blood loss). No significant difference was seen in haemoglobin levels (P = 0.677) and uterine tone. Fifteen, six and nine patients, respectively, required additional oxytocin (P = 0.151). The incidence of tachycardia (P = 0.726), hypotension (P = 0.321) and nausea/vomiting (P = 0.161) was comparable. To conclude, 5 IU/hour was more effective than 1.25 IU/hour in reducing total blood loss and the incidence of minor postpartum haemorrhage. Thus 5 IU/hour appears to be an optimal oxytocin infusion rate following 1 IU slow intravenous oxytocin injection for the maintenance of adequate uterine contraction in patients undergoing elective caesarean section under spinal anaesthesia.
Keywords: C-section; Oxytocin; blood loss; postpartum haemorrhage; uterotonic.