Effect of a High-Rate Versus a Low-Rate Oxytocin Infusion for Maintaining Uterine Contractility During Elective Cesarean Delivery: A Prospective Randomized Clinical Trial

Abstract

Introduction Oxytocin is routinely used as prophylaxis against uterine atony. During elective cesarean delivery (CD), an oxytocin bolus is used to initiate adequate uterine tone, followed by an oxytocin infusion to maintain uterine contractility. However, it is unclear whether oxytocin maintenance infusion rate influences total estimated blood loss (EBL). Methods We performed a prospective, randomized, double-blind trial in 51 women undergoing elective CD. Women were randomized to receive an oxytocin maintenance infusion of 2.5 u/hr or 15 u/hr. All women received an oxytocin 1 u bolus to initiate adequate uterine tone. The primary outcome was EBL. EBL values between groups were compared using a Mann-Whitney U test; P<0.05 as statistically significant. The median EBL difference with 95% confidence intervals (CI) was also calculated. Secondary outcomes included: adequacy of uterine tone, use of additional uterotonics, and oxytocin related side-effects, including hypotension. Results Of 51 women, 24 received a low rate infusion and 27 received a high rate infusion. Median [interquartile range] EBL values in the low rate and high rate groups were: 634 [340 – 886] ml vs. 512 [405 – 740] ml, respectively; P=0.7). The median difference in EBL between groups was 22 ml; 95% CI=−158 – 236 ml. The rate of postpartum hemorrhage did not differ between groups (low rate group: 4/24 (16.7%) vs. high rate group: 4/26 (15.4%)). There were no between-group differences over time (first 20 min after commencing infusion) in the incidence of adequate uterine tone (P=0.72) or hypotension (P=0.32). Conclusion Among women undergoing elective CD receiving an oxytocin maintenance infusion, EBL and uterine tone did not differ between women receiving 2.5 u/hr oxytocin to those receiving 15 u/hr oxytocin. Our findings suggest that efficacy can be obtained with a low oxytocin maintenance infusion rate, however dose-finding studies are needed to determine the infusion rate that optimizes drug efficacy whilst minimizing side effects.

The ED50 and ED95 of oxytocin infusion rate for maintaining uterine tone during elective caesarean delivery: a dose-finding study

“…After clamping of the umbilical cord and delivery of the infant, all parturients were given an i.v. bolus of oxytocin 1 IU over 15 s as previously recommended [6], after which the oxytocin infusion previously prepared according to the randomization scheme was initiated at 50 ml h − 1 .…”

“…Secondary outcomes included estimated blood loss (EBL), hemoglobin (Hb) and haematocrit (HCT) levels (at time of PACU discharge and on postoperative day 1), proportion of participants requiring administration of supplemental oxytocin boluses or alternative uterotonic agents, and side effects (hypotension, bradycardia, tachycardia [defined as HR ≥120 beats min − 1 ], nausea, vomiting, flushing, chest pain, or dyspnea). Postpartum hemorrhage (PPH), defined as EBL > 1000 ml [6], and the need for perioperative blood transfusion were also noted. EBL was estimated using the following formula [4, 9]: EBL (mL) = [(preoperative HCT - postoperative HCT)/preoperative HCT] × (weight in kilograms) × 85.…”

Intrapartum oxytocin: time to focus on longer term consequences?

“…However, their advice to administer a repeat dose (of 3 IU) as early as two minutes after delivery if uterine tone is inadequate, would probably result in many patients receiving 6 IU (often unnecessarily) in the first three minutes, rendering this a relatively moot point. They do not provide evidence to support their choice of a 2‐min assessment and we could only find three studies from the dose‐finding literature that provide data on assessments this early after oxytocin administration and none strongly support it. The expert consensus statement advises lower ‘maintenance’ infusion rates after an initial bolus: 2.5–7.5 IU.h −1 and 7.5–15 IU.h −1 , in elective and intrapartum caesarean delivery, respectively.…”

<p>The Median Effective Dose of Oxytocin Needed to Prevent Uterine Atony During Cesarean Delivery in Elderly Parturients</p>

“…10 We chose to study the ED 50 of oxytocin by bolus because 1) this mode of administration, rather than an infusion, is common in China and 2) very low doses are required by infusion after an initial bolus. 21 Bobrowski et al have performed a retrospective review of antepartum and delivery data of 9556 singleton pregnancies of women aged 20 to 29 or ≥35 years who delivered over 8 years, and found the elderly gravidas had the greatest age-related increases in oxytocin use (1.7times). 22 Similarly, in the current study, parturients in the old group had a higher initial bolus dose of oxytocin, total oxytocin requirements, and estimated blood loss than those in the young group.…”

“… 10 We chose to study the ED 50 of oxytocin by bolus because 1) this mode of administration, rather than an infusion, is common in China and 2) very low doses are required by infusion after an initial bolus. 21 …”