In Vitro Myometrial Contractions in Laboring and Non-laboring Women

In Vitro Myometrial Contractions in Laboring and Non-laboring Women: Oxytocin is Superior to Other Uterotonic Agents

The purpose of this study is to compare the ability of an isolated sample of uterine muscle tissue (in a tissue bath) to contract in the presence of various drugs. The drugs studied--uterotonics--are typically used to contract the uterus when a pregnant patient continues to bleed after delivery. Amongst common uterotonic drugs, namely oxytocin, ergonovine, prostaglandin F2alpha, and misoprostol, the most effective one to use is unknown. The investigators will be testing isolated uterine muscle samples to increasing concentrations of these four drugs in three patient populations: non-laboring, laboring without exogenous oxytocin augmentation, and laboring with oxytocin augmentation. Contractile measures will be measured and compared between all groups. The investigators hypothesize that oxytocin alone will have a weaker uterotonic effect in oxytocin-augmented laboring patients, and all four drugs will induce different patterns of contractions.

Postpartum hemorrhage (PPH) is a major cause of maternal mortality and morbidity. In 80% cases of PPH, the primary cause is failure of the uterus to contract after delivery of the baby, which then requires further treatment of the mother with uterotonic drugs (drugs used to contract uterus and thus prevent bleeding). Patients participating in this study will be asked to donate a very small sample of uterine tissue during Cesarean section, which will be tested in the laboratory for the ability to contract in response to the uterotonics oxytocin, ergonovine, prostaglandin F2alpha, and misoprostol. We will seek to better understand the effects of these drugs by comparing their contractile capability in isolated uterine tissue.

Uterine contraction, Dose response, Non-laboring, Laboring, Laboring with oxytocin augmentation, Oxytocin, Ergonovine, Prostaglandin F2alpha, Misoprostol

All samples will undergo dose response treatment (increasing concentrations) of one of the four uterotonic drugs: oxytocin, ergonovine, prostaglandin F2alpha, or misoprostol.

Oxytocin, 10-10mol/L to 10-5mol/L; solution made in double-distilled autoclaved water and then tested in physiological salt solution.

Ergonovine, 10-10mol/L to 10-5mol/L; solution made in double-distilled autoclaved water and then tested in physiological salt solution.

Prostaglandin F2alpha, 10-10mol/L to 10-5mol/L; solution made in double-distilled autoclaved water and then tested in physiological salt solution.

Misoprostol, 10-10mol/L to 10-5mol/L; solution made in double-distilled autoclaved water and then tested in physiological salt solution.

Inclusion Criteria: Gestational age 37-41 weeks Patients requiring primary or first repeat Cesarean section Cesarean section under spinal anesthesia Exclusion Criteria: Patients who require general anesthesia Patient who had previous myometrial surgery or more than one previous Cesarean section Patients with placental anomalies Patients with multiple pregnancy (twins, etc.)

Balki M, Erik-Soussi M, Kingdom J, Carvalho JC. Comparative efficacy of uterotonic agents: in vitro contractions in isolated myometrial strips of labouring and non-labouring women. Can J Anaesth. 2014 Sep;61(9):808-18. doi: 10.1007/s12630-014-0190-1. Epub 2014 Jun 7.