Maternal Hemodynamics After Oxytocin Bolus Compared With Infusion in the Third Stage of Labor: A Randomized Controlled Trial

Abstract

To assess the effects of oxytocin bolus or infusion on maternal hemodynamics in the third stage of labor. In a randomized, double-blind, double-dummy fashion, 99 women received an intravenous oxytocin bolus (10 IU push) and 102 women received an infusion (10 IU in 500 mL saline at 125 mL/h) at delivery of the anterior shoulder. Mean arterial pressure and heart rate were measured every minute for 10 minutes, then every 5 minutes for the next 20 minutes. These serial measurements were analyzed using a 2-factor analysis of variance for repeated measures. Serial mean arterial pressure measures varied significantly between groups (interaction effect, P = .002). Mean arterial pressure (+/- standard deviation) nadirs were reached after 10 minutes, 80.9 (+/- 11.0) mm Hg in the bolus group compared with 77.0 (+/- 12.1) mm Hg in the dilute infusion group. The mean difference (95% confidence interval) between groups was 4.0 (0.7-7.2) mm Hg. Serial heart rate measures also varied between groups (interaction effect, P < .001). Mean heart rate (+/- standard deviation) peaked 1 minute after the oxytocin infusion, 115 (+/- 27) beats per minute (bpm) in the bolus group compared with 109 (+/- 21) bpm in the dilute infusion group. The mean difference (95% confidence interval) between groups was 6.6 bpm (-0.1 to 13.3). The dilute oxytocin infusion group experienced a greater mean estimated blood loss (423.7 mL compared with 358.1 mL, P = .029, t test), increased use of additional oxytocics (35.3% compared with 22.2%, P = .044, Fisher exact test) and a greater drop in hemoglobin (admission minus postpartum) (17.4g/L compared with 11.4g/L, P = .002, t test) compared with the oxytocin bolus group. Bolus oxytocin of 10 IU is not associated with adverse hemodynamic responses and can safely be administered to women with intravenous access in the third stage of labor for postpartum hemorrhage prophylaxis. I.