Oxytocin

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:

• Initiation (induction) of labor, whenever the benefits of delivery exceed the risks of continuing intrauterine existence.

• Stimulation (augmentation) of labor, whenever labor abnormalities such as prolonged latent phase or arrest of the active phase occur.

• Control of postpartum hemorrhage or prophylaxis for such control, following delivery of the fetus and placenta.

• Providing enough contractions to assess fetal well-being in the context of a contraction stress test.

• Assistance of milk let-down in postpartum, breastfeeding women (This is an infrequent use.)

• 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:

• There is an unfavorable fetal position or presentation which is undeliverable without conversion prior to delivery

• Vaginal delivery is contraindicated (invasive cervical carcinoma, active genital herpes, total placenta previa or vasa previa)

• There is an obstetrical emergency where the risk-to-benefit ratio of maternal and fetal safety favors surgical intervention

In far forward military settings, a controlled infusion pump may not be available for delivery of oxytocin. In such cases, some low-tech approaches may be useful:

1. Nipple stimulation (rolling the nipple back and forth with thumb and forefinger) will cause of release of the mother's own oxytocin from her pituitary gland. This will have the effect of stimulating contractions. Stimulating both nipples will have about double the effect as stimulating one nipple. After about 15-20 minutes of nipple stimulation you will have released about as much natural oxytocin as is available. Nipple stimulation can be repeated at a later time, after the natural oxytocin supply has been replenished.

   1. While this technique can be effective, the biggest problem is overstimulation of the uterus because of too much oxytocin. Rather than achieving more frequent, longer contractions, you will end up with a single, 3-5 minute contraction that is threatening to the fetus and the integrity of the uterus.

   2. Start with stimulation of just one nipple. Have the mother perform this on herself. It usually takes 3-5 minutes of this before you will notice any effect on the uterus. If gentle nipple stimulation is not effective, increase the strength of the nipple massage. If there is still no result, you can try stimulating both nipples. Just make sure to give the uterus enough time to respond.
       

2. Amniotomy (artificial rupture of the bag of waters) can also be a  effective stimulus to labor. Amniotomy may be safely performed if the fetal head is sufficiently engaged in the maternal pelvis to keep the umbilical cord from slipping past it, creating a prolapsed cord situation.
    

3. Open drip oxytocin, largely abandoned in the United States 30 years ago for safety reasons, can still be effectively employed, if you are very careful with it.

   1. Put 10 units (1 amp) of oxytocin in 1 Liter of IV fluid (NS, LR, D5W, etc.) and mix it well.

   2. Piggyback the oxytocin solution into a mainline IV (of any type), running at 100-125 cc per hour.

   3. While monitoring the uterine contractions (with electronic fetal monitoring, if available, or with your hand on the mother's abdomen if EFM is not available), open the oxytocin IV just enough to allow 3 drops to enter the mainline.

   4. Wait a few minutes to assess the impact of these 3 drops.

   5. If there is no measurable impact after a few minutes, then allow several more drops to infuse. Keep you hand on the patient's abdomen so that you can monitor the contractions.

   6. Gradually increase the oxytocin flow rate until you achieve regular uterine contractions every 2.5 to 3 minutes, lasting about 60 seconds. While increasing the flow rate, allow several minutes after each change in rate to evaluate the impact on uterine contractions.

   7. If the contractions last longer than 60 seconds, slow or stop the oxytocin.

   8. If the contractions consistently occur more often than every 2 minutes, slow or stop the oxytocin.

   9. If the patient experiences uterine tetany (continuous contractions), stop the oxytocin.

   10. The fetal heart should be monitored during this time, preferably with EFM, but listening to the rate every 15 minutes can also be effective.

   11. Open drip oxytocin is considered more dangerous than when used with a controlled infusion pump because:

       1. It is easier for the oxytocin flow to increase suddenly, causing too many contractions and stresses on the uterus.

       2. There is greater risk of uterine rupture without the constant controlled flow of an infusion pump.

       3. In the end, so long as you monitor the patient and provide a reasonably controlled, steady but titratable delivery of dilute oxytocin, you will  be helpful to those who need oxytocin stimulation but were unfortunate enough to be in a location that does not have all of the safety features found in the Continental United States.