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Uterine Stimulants

Uterine stimulants

Definition

Uterine stimulants (uterotonics) are medications that cause, or increase the frequency and intensity of, uterine contractions. These drugs are used to induce (start) or augment (stimulate) labor, facilitate uterine contractions following a miscarriage , induce abortion, or reduce hemorrhage following childbirth or abortion. The three uterotonics used most frequently are oxytocins, prostaglandins, and ergots. Depending upon the type of drug, uterotonics may be given intravenously (IV), intramuscularly (IM), as a vaginal gel or suppository, or in oral form.

Purpose

Uterine stimulants are used to induce, or begin, labor in certain circumstances when the mother has not begun labor naturally. These circumstances may include if the mother is post-dates, that is, gestation that is over 40 weeks—especially if tests indicate a decrease in amniotic fluid volume. They may be used in cases of premature rupture of the membranes, preeclampsia (elevated blood pressure in the late stage of pregnancy ), diabetes, and intra-uterine growth retardation (IUGR) when these conditions require delivery before labor has begun. They may be recommended if the expectant mother lives a great distance from the healthcare facility and there is concern for either her or her baby's safety if she were unable to reach the facility once labor begins. They are also used in the augmentation of existing contractions to increase strength and frequency when labor is not progressing well.

According to the American College of Obstetrics and Gynecology (ACOG), the 1990s saw an increase in the rate of induced labor—from 9% to 18%. In a May 31, 2001, statement, the ACOG reported that the increase in the cesarian rate seen over the same period of time was not due to the induction process but to other factors, such as the condition of the cervix at the time of induction and whether or not the pregnancy was the woman's first.

Oxytocin and prostaglandin (PG) are naturally occurring hormones used to induce labor. They are also available in synthetic form (Pitocin and Syntocinon are the synthetic counterparts of oxytocin). PG is also used to ripen the cervix prior to induction, which is sometimes sufficient to stimulate labor, and the woman needs no further medication for labor to progress. There are many forms of PGs, but those of greatest interest are PGE1, PGE2, and PGF2 alpha. Research is investigating which are the most effective for which process. For example, PGE2 in the form of dinoprostone (Cervidil and Prepidil) has proven superior to the PGF series in cervical ripening. Misoprostol (Cytotec), a synthetic PGE1, also is effective in cervical ripening and labor induction, while the PGF2 alpha analog, carboprost (Prostin 15-M, or Hemabate), is the preferred PG uterine stimulant. The ergots, which significantly increase uterine activity, have severe side effects in many women. Only one ergot, methylergonovine maleate (Methergine) is now used in the United States, and is used only to control postpartum hemorrhage (PPH).

Oxytocin is also used in a contraction stress test (CST). This is done prior to the onset of labor to evaluate the fetus's ability to handle uterine contractions. To avoid the possibility of exogenous (introduced) oxytocin putting the woman into labor, she may instead be asked to stimulate her nipples to cause the release of natural oxytocin. A negative, or normal, test is one in which there are three contractions in a 10-minute period, with no abnormal slowing of the fetal heart rate (FHR). False positives of the CST do occur, however. Also, the expectant mother should remain in the health care setting for about half an hour after a negative test to make sure the test did not stimulate labor.

If a woman has a miscarriage, oxytocin may be used to bring on contractions to assure that all the products of conception (POC) are expelled from the uterus. If the fetus died but was not expelled, prostaglandin (PGE2) may be used to ripen the cervix to facilitate a dilatation and evacuation, and/or to encourage more uterine contractions. In this case, prostaglandin may be used either in gel form or as a vaginal suppository.

In a routine delivery oxytocin may be ordered after the placenta has been delivered in order to increase uterine contractions and minimize bleeding. Oxytocin (Pitocin) also may be used to treat uterine hemorrhage. While hemorrhage occurs in about 4% of vaginal deliveries and 6% of cesarian deliveries, it accounts for about 35% of maternal deaths due to bleeding during pregnancy. The role of oxytocin is to bring on and strengthen uterine contractions. If the hemorrhage stems from the placental detachment site, contractions help to close off the blood vessels and thereby stop the excessive bleeding. Additional medications may be used, including PGF2 alpha (Hemabate), misoprostol (Cytotec), or the ergot methylergonovine (Methergine). If the uterus is contracted but bleeding continues, the cause may be retained placenta, genital tract laceration, or uterine rupture. Large clots that remain in the lower part of the uterus can inhibit the uterus from contracting, leading to uterine atony (lack of tone or tension), a leading cause of postpartum hemorrhage. Uterine contractions also help to expel large clots and placental fragments.

Precautions

It is important to establish a clear baseline of vital signs before a woman is given any medication to induce labor. Consistent reevaluation and documentation of vital signs allow for faster recognition of an abnormal change in a woman's condition. Also, a clear labor and delivery record will assist the postpartum nurse in monitoring for changes as well. Documentation includes time and dosage of any medications given, as well as any side effects that might occur. Proper documentation will help avoid the chance of medication doses being given too close together. An increasing pulse and a decreasing blood pressure signal a potential hemorrhage. When oxytocin is given IV, it must be diluted in IV fluid and never given as a straight IV. PGs should not be given if there is any question about fetal well-being, for example, an abnormal FHR tracing. The ergot, Methergine, should never be given via IV and never to a woman with hypertension .

Description

Oxytocin

Oxytocin's major functions are in labor and lactation . In vitro, production and secretion of oxytocin is stimulated by the pituitary gland . Just what happens to initiate labor remains a mystery, even although much research has focused on this area. The hormone estrogen appears to increase the number of oxytocin receptors as the gestation period increases. The degree to which uterine muscles are sensitive to oxytocin's action appears linked to the number of oxytocin receptors. Oxytocin levels increase as labor progresses, and the fetus also secretes oxytocin during labor, increasing the amount of circulating oxytocin.

In a normally progressing labor, contractions become more frequent, more intense, and last longer. In a dysfunctional labor, contractions may weaken, become further apart, or even stop. A prolonged labor puts the mother at risk of fatigue, which can increase the likeli-hood of a cesarian delivery or fetal distress. Oxytocin may be given to augment the labor. Some women may need only a very small amount in order to "jump start" labor once again. For others it may be necessary to continue the oxytocin in small increments. Oxytocin increases the strength, duration, and frequency of contractions, so care must be taken to prevent the contractions from becoming too strong or too frequent. If the mother has an infection , labor may not progress as usual. Oxytocin is less effective in such cases.

Naturally occurring oxytocin plays a role in breast-feeding by facilitating both milk ejection and the letdown reflex. When the neonate suckles at the breast, the nipple stimulation sends a message to the pituitary gland to release oxytocin. Oxytocin then causes the milk gland cells to constrict, pushing the milk forward towards the nipples. Breastfeeding immediately after delivery encourages oxytocin production and causes uterine contractions, helping the uterus to become firm and close off the blood vessels at the placental detachment site. This process limits the amount of blood lost after childbirth. Because the release of oxytocin is inhibited by fear, pain , embarrassment, and distraction, providing the new mother with a calm environment in which she can focus on her infant will facilitate breastfeeding and the production of oxytocin.

Prostaglandins

Prostaglandins play a major role in the stimulation of uterine contractions that begin the labor process. Research indicates that PGs also facilitate the mother's transition between phases of the labor process. Some PGs promote vasoconstriction while others promote vasodilation. One function of PGs is to promote cervical effacement and dilation during labor. Oxytocin plays a role in stimulating the release of PGs. Infection stimulates their release, also, which appears to be a factor in the initiation of up to 30% of cases of preterm labor . PGs serve a function in immunosuppression, but the exact mechanism is unclear. They also may be a major factor in regulating umbilical blood flow by keeping the ductus arteriosus open during fetal life.

Ergots

Ergots are produced by a fungus that forms primarily on rye grain. Because of its potentially harmful side effects, one form (Ergonovine, or Ergotrate) was taken off the market in 1993 and methylergonovine maleate (Methergine) is now the only form used, and is used only as a uterine stimulant to control PPH. (There is no evidence that Methergine used as a prophylactic decreases the risk of PPH.) Even so, because of the complications it can cause, and because its use is contraindicated in a large number of women, Methergine has been replaced by the PGs as the second-line uterotonic of choice.

Preparation

Before any procedure is begun or medication administered, it is important for the nurse to review the information with the pregnant woman to ensure she understands what will take place and the potential side effects of the medication. Any allergies to medication need to be reviewed, as well as any prior response the mother may have had to the medications. The mother may be anxious about induction or augmentation, fearing that the contractions will come too fast or that she will feel out of control of the process. The nurse needs to address her concerns, as well as those of her partner.

Aftercare

Close supervision of the mother during induction or cervical ripening must take place. The FHR and uterine contractions are usually monitored for an hour after induction. Frequent checks of vital signs alert the nurse to any potential complications.

Complications

Oxytocin

The effect of IV oxytocin is rapid following administration. The individual response to oxytocin can vary considerably and administration is usually increased slowly and incrementally. Hyperstimulation of the uterus, which can result from oxytocin augmentation, can place the fetus at risk for asphyxia. Hyperstimulation is defined as more than five contractions in 10 minutes, contractions lasting longer than 60 seconds, and increased uterine tonus either with or without significant decrease in FHR. Uterine rupture has also been linked to oxytocin administration, particularly for periods longer than four hours. Oxytocin has a small antidiuretic effect that is usually dose related and that can lead to water intoxication (hyponatremia). Onset occurs gradually and may go unnoticed. Signs may include reduced urine output, confusion, nausea, convulsions, and coma . Mothers receiving oxytocin need to have their blood pressure monitored closely, as both hypotension and hypertension can occur, and—although the subject remains controversial—evidence suggests oxytocin increases the incidence of neonatal jaundice . Although oxytocin may put women with a classical cesarian section scar from a prior delivery at increased risk of uterine rupture, contraindications to the use of the drug are virtually the same as contraindications for labor. Other side effects of oxytocin include nausea, vomiting, cardiac arrhythmias, and fetal bradycardia. When used judiciously oxytocin is a very effective medication for the progression of labor.

Prostaglandins

Significant systemic side effects are associated with the use of PGs. These include headache, nausea, diarrhea , tachycardia, vomiting, chills, fever , sweating, hypertension, and hypotension. There is also increased incidence of uterine hyperstimulation and potential for uterine rupture. PGF2 alpha (carboprost—Prostin 15-M or Hemabate) can cause hypotension, pulmonary edema , and—in women with asthma—intense bronchospasms. Because it stimulates the production of steroids, carboprost may be contraindicated in women with adrenal gland disease. When used for abortion it may result in sufficient blood loss to cause anemia, necessitating a transfusion. Medical problems (or history) of diabetes, epilepsy, heart or blood vessel disease, jaundice , kidney disease, or liver disease should be brought to the attention of the health care practitioner before the use of carboprost. Also, in rare instances, ophthalmic pressure has increased in women with glaucoma with the use of this PG.

Ergots

Ergots have an alpha adrenergic action with a vasoconstricive effect. They can cause hypertension, cardiovascular changes, cyanosis , muscle pain, tingling, other symptoms associated with decreased blood circulation, and severe uterine cramping. The health care professional should be well aware of other medications being taken by the patient; the presence or history of medical problems such as angina, hypertension, stroke, infection, kidney and liver disease, and Raynaud's phenomenon may be contraindications to the use of this drug.


KEY TERMS


Atony —In uterine atony, the uterus fails to contract after delivery, remaining relaxed. This flaccid condition can lead to hemorrhage, and puts the mother at risk of shock and death.

Augment —Drugs to augment labor are given after labor has begun, but fails to progress, or when the contractions have slowed down and are weak or ineffective, prolonging labor unnecessarily.

Hemorrhage —The loss of an excessive amount of blood in a short period of time. After childbirth, a loss of more than 500 mL over a 24-hour period is considered postpartal hemorrhage. The blood loss may be sudden and swift, or slow and continuous.

Induce, induction —To begin or start.

Post-dates —Gestation longer than approximately 40 weeks. Up to 42 weeks may still be still considered normal.


Results

Anticipated outcomes for uterine stimulants are either to prepare the cervix for childbirth, induce or stimulate uterine contractions to produce a safe delivery of a newborn, encourage a complete spontaneous or induced abortion, eliminate blood clots or other POC debris from the uterus, and decrease or stop hemorrhage following childbirth or abortion. Normal results would meet these outcomes without significant side effects—either for the mother or, in the case of childbirth, the infant.

Heath care team roles

Nurses play a major role in preparing the patient for, and administering, uterine stimulants and monitoring the patient and fetus during the labor process. Because the choice of drug, its form of administration, and its side effects varies, knowledge of uterine physiology is an important aspect of caring for women and their fetuses undergoing treatment with these drugs. Nurses must be aware of potential complications and side effects, as well as dosing requirements, criteria assessment, and contraindications to these drugs. They should take a complete medical history of the patient, including prescription and over-the-counter medications, illnesses, and disease. In most instances a gynecologist or other qualified physician will perform the actual delivery, although this may occasionally be facilitated by a midwife. A pediatrician or family health care practitioner will examine the newborn infant and administer treatment if required. The nurse can be an important source of information and comfort to women facing induction of labor or abortion, and to new mothers facing the initial responsibility of parenthood.

Resources

BOOKS

Creasy, Robert K., and Robert Resnik. Maternal-Fetal Medicine, 4th ed. Philadelphia: W. B. Saunders Company, 1999.

Rakel, Robert A. Conn's Current Therapy 2000. Philadelphia: W.B. Saunders Company, 2000.

Scott, James. Danforth's Obstetrics and Gynecology 8th ed. Philadelphia: Lippincott Williams & Wilkins, 1999.

OTHER

American College of Obstetricians and Gynecologists (ACOG). 409 12th St. SW, PO Box 96920, Washington, DC 20090-6920. <http://www.acog.com>.

Esther Csapo Rastegari, R.N., B.S.N., Ed. M.

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