Oxytocin is the hormone most commonly administered to women on labor and delivery. It is used for induction of labor, augmentation of labor, and to reduce the risk of postpartum hemorrhage. Licensed independent prescribers, including physicians and nurse midwives, order oxytocin, and licensed professional nurses execute the order by administering the hormone. Optimal management of oxytocin infusion requires effective interprofessional communication and collaboration. During labor it is common for disagreements to arise between the professionals ordering and the professionals administering oxytocin. The disagreements are usually caused by differing perspectives on the appropriate oxytocin dose. Standardized protocols and checklists reduce practice variation and improve patient safety.
Oxytocin hormone
Oxytocin is a cyclic nonapeptide synthesized in the hypothalamus and secreted into the circulation from axonal terminals in the posterior pituitary. In the myometrium, oxytocin activates a membrane G protein-coupled receptor, increasing phospholipase C and intracellular calcium. Following several intracellular chemical cascades, oxytocin stimulation results in myosin and actin filaments sliding over each other initiating shortening of the smooth muscle cell. Myometrial smooth muscle cells are connected by gap junctions, facilitating the coordinated contraction of the uterus.1
Oxytocin pulse frequency and uterine oxytocin receptor concentration both increase during pregnancy and labor, facilitating the birth process. Oxytocin pulse frequency increases from 2.4 pulses per hour before labor to 13.4 pulses per hour in the second stage.2 In addition, uterine oxytocin receptor concentration increases 12-fold from the early second trimester of pregnancy to term.3
Oxytocin has a half-life of approximately 10 to 15 minutes. Many pharmacologists believe that for a given dose of a drug, it takes 4 to 5 half-lives for a stabilized circulating concentration to be achieved. Therefore, during an oxytocin infusion, when the dose is increased it may take 40 to 50 minutes to achieve a new higher, stabile circulating concentration.4
Low-dose vs high-dose oxytocin protocols
Oxytocin is often used in a premixed solution of 30 units of oxytocin in 500 mL of lactated Ringer’s solution. With this mixture, an infusion of 1 mL/hour results in the administration of 1 mU of oxytocin per minute (1 mU/min). There is no national consensus on an optimal oxytocin infusion regimen for induction or augmentation of labor. A commonly used low-dose regimen is an initial dose of 1 to 2 mU/min, with a dose increase of 1 to 2 mU/min every 30 to 40 minutes until regular uterine contractions occur every 2 to 3 minutes.5 An example of a high-dose oxytocin regimen is an initial dose of 6 mU/min with an increase of 3 to 6 mU/min every 30 to 40 minutes (induction of labor).6
A randomized trial reported that, compared with a low-dose oxytocin regimen, a high-dose regimen increased the risk of tachysystole without a significant change in cesarean birth rate.7 A Cochrane review concluded that, compared with low-dose regimens, high-dose oxytocin regimens were more likely to be associated with tachysystole.8 Based on these reports, I would suggest avoiding the use of a high-dose oxytocin regimen. Experts have reported that an oxytocin dose of approximately 6 mU/min achieves a circulating oxytocin concentration similar to that observed in normal spontaneous labor.9
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