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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.
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Oxytocin is indicated for the:
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Initiation (induction) of labor, whenever the benefits of delivery
exceed the risks of continuing intrauterine existence.
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Stimulation (augmentation) of labor, whenever labor abnormalities such
as prolonged latent phase or arrest of the active phase occur.
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Control of postpartum hemorrhage or prophylaxis for such control,
following delivery of the fetus and placenta.
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Providing enough contractions to assess fetal well-being in the context
of a contraction stress test.
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Assistance of milk let-down in postpartum, breastfeeding women (This is
an infrequent use.)
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To help complete an incomplete abortion, or control bleeding following a
complete abortion.
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:
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There is an unfavorable
fetal position or presentation which is undeliverable without conversion
prior to delivery
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Vaginal delivery is
contraindicated (invasive cervical carcinoma, active genital herpes, total
placenta previa or vasa previa)
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There is an obstetrical
emergency where the risk-to-benefit ratio of maternal and fetal safety
favors surgical intervention
Amniotomy is
sometimes performed in conjunction with oxytocin administration to stimulate
uterine contractions. |
