• J B Sartain, J J Barry, P W Howat, D I McCormack, and M Bryant.
• Department of Anaesthesia, Intensive Care and Perioperative Medicine, Cairns Base Hospital, The Esplanade, Cairns, QLD 4870, Australia. james_sartain@health.qld.gov.au
• Br J Anaesth. 2008 Dec 1;101(6):822-6.

BackgroundThe optimal dose of oxytocin at Caesarean section is unclear. Oxytocin may cause adverse cardiovascular effects, including tachycardia and hypotension, whereas an inadequate dose can result in increased uterine bleeding. We compared the effects of two doses of oxytocin in a randomized double-blind trial.MethodsEighty patients undergoing elective Caesarean section received an i.v. bolus of either 2 or 5 units (u) of oxytocin after delivery, followed by an oxytocin infusion of 10 u h(-1). All received combined spinal-epidural anaesthesia with arterial pressure maintained by a phenylephrine infusion. We compared changes in heart rate (HR), mean arterial pressure (MAP), blood loss, uterine tone, the need for additional uterotonic drugs, and emetic symptoms.ResultsThere was a greater increase in mean (sd) HR in patients who received 5 u of oxytocin [32 (17) beats min(-1)] than in those who received 2 u [24 (13) beats min(-1)] (P=0.015). There was a larger decrease in MAP in patients who received 5 u [13 (15) mm Hg] than in those who received 2 u [6 (10) mm Hg] (P=0.030). The frequency of nausea and antiemetic use was higher after 5 u (32.5%) than 2 u (5%) (P=0.003). There were no differences in blood loss, uterine tone, or requests for additional uterotonic drugs (17.5% in both groups).ConclusionsIn elective Caesarean section, a 2 u bolus of oxytocin results in less haemodynamic change than 5 u, with less nausea and no difference in the need for additional uterotonics.

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