Oxytocin is a naturally-occurring hormone that stimulates the smooth muscle of the uterus to contract. It is most effective at term when the uterine muscle is most sensitive, but it can have stimulatory effects even early in pregnancy. Oxytocin is used to induce labor, to stimulate pre-existing labor, and as a uterotonic agent to reduce postpartum bleeding.
During labor, the usual effects of administering oxytocin are to make the contractions stronger, more frequent, and of longer duration. Of these, the most desirable for labor is the increased frequency. If too much oxytocin is given, the contractions may occur so frequently that there is too little time for utero-placental resupply of oxygen and removal of carbon dioxide. If needed to stimulate labor and not enough oxytocin is given, then the abnormal labor may continue. The dosage of oxytocin must be titrated to just the right amount...not too much and not too little.
To aid in achieving just the right dose, a dilute solution of oxytocin is often administered by a controlled infusion pump. The precise amount of oxytocin delivered is less important than the consistency of dosing. As some uteruses are very sensitive to even small doses, a small dose is initiated, and then gradually increased until the desired effect is achieved (contractions every 2 1/2 to 3 minutes, lasting close to 60 seconds, with peak strength of at least 60 mm Hg.). Although usually given intravenously, other forms of administration may be appropriate in some clinical circumstances.
If the contractions are too frequent (>10 contractions in 20 minutes), or the uterus fails to completely relax between contractions, then the oxytocian infusion rate is adjusted downward. As labor progresses, this is often the case, and many patients will receive oxytocin for much of their labor only to have it turned off at the end of labor because they no longer need it. If overstimulation of the uterus occurs, not only can this adversely affect fetal oxygen exchange through the placenta, but uterine rupture can occur.
Following delivery of the baby and placenta, oxytocin is commonly given in moderate doses to control uterine bleeding. In this case, overstimulation of the uterus is not a concern.
Oxytocin can have other, non-obstetrical effects. The most important of these is an anti-diuretic-hormone-like effect, sometimes seen after prolonged administration of relatively high doses of oxytocin and large volumes of crystalloid.
Oxytocin is indicated for the:
Oxytocin is usually not given in the presence of known cephalopelvic dysproportion, fetal distress, or other conditions in which the increase in frequency, strength and duration of contractions is ill-advised. It is also not usually given when:
Amniotomy is sometimes performed in conjunction with oxytocin administration to stimulate uterine contractions.
OB-GYN 101: Introductory
Obstetrics & Gynecology
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