Oxytocin binds to a G-protein–coupled receptor. Activation triggers elevation of intracellular calcium that stimulates uterine smooth muscle contraction. Its function is regulated by:
Changes in receptor expression
Receptor internalization leading to oxytocin desensitization
Local changes in oxytocin concentration
The effects of oxytocin on vascular smooth muscles depend on types of vasculatures and vascular basal tones. While oxytocin induces uterine contractions, higher concentration of oxytocin relaxes the high-resistance vasculatures of skeleton muscles, liver, kidney, and spleen.1 Rapid injection of a large dose of oxytocin in severe hypovolemic patients with postpartum hemorrhage may result in worsening hypotension, myocardial ischemia, circulatory collapse, and even maternal death.2
Large total oxytocin doses should be avoided to minimize the antidiuretic effect. The patient on high dose of oxytocin for induction of labor for a prolong period could be at increased risk to develop severe hyponatremia or seizure.
DOSAGE AND ADMINISTRATION
Dosage and Administration3
Standardized oxytocin protocols have been shown to reduce the incidence of postpartum hemorrhage.4 Oxytocin should be given as a small initial dose after delivery, followed by a controlled infusion. Oxytocin dose requirements are higher for intrapartum cesarean deliveries.5 FDA mandates to use infusion pump for oxytocin administration (Fig. 4-1).
Administration of oxytocin for cesarean delivery.
A second-line medication (ergot or prostaglandins) should be considered EARLY if oxytocin fails to produce good uterine tone.
BT. Actions of vasopressin, oxytocin, and synthetic analogs on vascular smooth muscle. Fed Proc.
SM. Effect of the confidential enquiries into maternal deaths on the use of Syntocinon at caesarean section in the UK. Anaesthesia
et al. International consensus statement on the use of uterotonic agents during caesarean section. Anaesthesia
et al. A standardized oxytocin administration protocol after delivery to reduce the treatment of postpartum hemorrhage. Jt Comm J Qual Patient Safety. 2019;45:131–143.
CA. The ED90 of prophylactic oxytocin after delivery of the placenta during Cesarean delivery in laboring compared with nonlaboring women: an up-down sequential allocation dose-response study. Anesth Analg.