Labor, oxytocin

Oxytocin is a peptide hormone secreted by the posterior pituitary that elicits milk ejection in lactating women. It may contribute to the initiation of labor. Oxytocin is released during sexual orgasm. 

Oxytocin is frequently given to induce and maintain labor after the cervix has ripened naturally or with the aid of misoprostol. For induction of labor, oxytocin should be administered intravenously via an infusion pump with appropriate fetal and maternal monitoring. An initial infusion rate of 1 mU/min is increased every 15-30 minutes until a physiologic contraction pattern is established. The maximum infusion rate is 20 mU/min. For postpartum uterine bleeding, 10-40 units is added to 1 L of 5% dextrose, and the infusion rate is titrated to control uterine atony. Alternatively, 10 units can be given intramuscularly after delivery of the placenta. To induce milk let-down, one puff is sprayed into each nostril in the sitting position 2-3 minutes before nursing. 

Two cysteine residues may form a disulfide bridge within a single peptide chain, making a ring. Figure 24-9 shows the structure of human oxytocin, a peptide hormone that causes contraction of uterine smooth muscle and induces labor. Oxytocin is a nonapeptide with two cysteine residues (at positions 1 and 6) linking part of the molecule... 

Oxytocin is contraindicated in patients with known hypersensitivity to the drug, cephalopelvic disproportion, unfavorable fetal position or presentation, in obstetric emergencies, situations of fetal distress when delivery is not imminent, severe toxemia (preeclampsia, eclampsia), hypertonic uterus, during pregnancy (intranasal administration), when there is total placenta previa, or to induce labor when vaginal delivery is contraindicated. Oxytocin is not expected to be a risk to the fetus when administered as indicated. When oxytocin is administered with vasopressors, severe hypertension may occur. 

Before starting an IV infusion of oxytocin for the induction of labor, the nurse obtains an obstetric history (parity, gravidity, previous obstetric problems, type of labor, stillbirths, abortions, live birth infant abnormalities)... 

Hyperstimulation of the uterus during labor may lead to uterine Many with marked impairment of the uteroplacental blood flow, uterine rupture, cervical rupture, amniotic fluid embolism, and trauma to the infant. Overstimulation of the uterus is dangerousto both the fetusand the mother and may occur even when the drug is administered properly in a uterus that is hypersensitive to oxytocin. 

OXYTOCIN The patient receiving oxytocin to induce labor may have concern over the use of the drug to produce contractions. When given to induce or stimulate contractions, oxytocin may only be given intravenously (IV). The nurse explains the purpose of the IV infusion and the expected results to the patient. Because the patient receiving oxytocin must be closely supervised, the nurse spends time with the patient and offers encouragement and reassurance to help reduce anxiety. 

Judith Watson, aged 28 years, is admitted to the obstetric unit and is to receive oxytocin to induce labor. This is her first child, and she is extremely anxious. Analyze what information would be necessary for her to receive from the nurse before the administration of oxytocin. What assessments would be important for the nurse to make during treatment with oxytocin ... 

The posterior pituitary is innervated by direct nervous stimulation from the hypothalamus, resulting in the release of specific hormones. The hypothalamus synthesizes two hormones, oxytocin and vasopressin. These hormones are stored in and released from the posterior pituitary lobe. Oxytocin exerts two actions (1) it promotes uterine contractions during labor, and (2) it contracts the smooth muscles in the breast to stimulate the release of milk from the mammary gland during lactation. Vasopressin is an antidiuretic hormone (ADH) essential for proper fluid and electrolyte balance in the body. Specifically, vasopressin increases the permeability of the distal convoluted tubules and collecting ducts of the nephrons to water. This causes the kidney to excrete less water in the urine. Consequently, the urine becomes more concentrated as water is conserved. 

Oxytocin is the most commonly used agent for labor induction after cervical ripening. 

The IV or IM administration of parenteral narcotics (meperidine, morphine, fentanyl) is commonly used to treat the pain associated with labor. Compared to epidural analgesia, parenteral opioids are associated with lower rates of oxytocin augmentation, shorter stages of labor, and fewer instrumental deliveries. 

Oxytocin, a hormone composed of nine amino acids, which induces labor by stimulating contraction of uterine muscles... 

Myometrial stimulants. The neurohypophyseal hormone oxytocin (p. 242) is given parenterally (or by the nasal or buccal route) before, during, or after labor in order to prompt uterine contractions or to enhance them. Certain prostaglandins or analogues of them (p. 

Extensive medicinal chemistry optimization of potency, selectivity pharmacokinetic, and pharmacodynamic properties finally led to potent, selective, and orally bioavailable GSK-221149A, which is synthesized as shown on Scheme 17 [35, 37, 38]. Peptidic oxytocin receptor antagonists are currently used to treat preterm labor, the main reason for infant death. The peptide derivatives by their nature are not orally bioavailable but must be administered i.v. Surprisingly, the peptide derivatives are less potent and less selective against several related receptors than GSK-221149A with half the molecular weight [39]. 

Leach CA, Liddle J, Peace S, Philp J, Smith lED, Terrell LR, Zhang J (2006) Preparation of l,6-disubstituted-(3R,6R)-3-(2,3-dihydro-lH-inden-2-yl)-2,5-piperazinedione derivatives as oxytocin receptor antagonists for the treatment of pre-term labor, dysmenorrhea and endometriosis. PCT Int Appl WO 2006067462 Al 20060629... 

Oxytocin is used for the induction of labor, or augmentation of labor in selected patients with uterine dysfunction, and to prevent or control bleeding after birth or abortion. Demoxytocin, a synthetic oxytocin has similar activities as oxytocin. 

Oxytocin also stimulates contraction of uterine smooth muscle in late phases of pregnancy. See Chapter 62 for a full discussion of the use of oxytocin in labor and delivery. 

Release of oxytocin at this stage of parturition promotes prostaglandin production, particularly of the E and F series, within the decidua these prostaglandins are powerful myometrial stimulants and thus further enhance uterine contractions. The prostaglandin concentration in maternal serum and amniotic fluid increases with the progression of labor. 

Oxytocin is generally considered to be the drug of choice for inducing labor at term. In combination with amniotomy, oxytocin is highly successful in inducing and augmenting labor. When given oxytocin, approximately 80% of patients with documented labor disor-... 

Oxytocin may be given by intravenous infusion (e.g., labor induction), intramuscular injection (e.g., control of postpartum bleeding), or as a nasal spray (e.g., to promote milk ejection). 

Because dinoprostone produces cervical ripening along with stimulation of the uterus, it has been used as an alternative to oxytocin for the induction of labor. Preparations of dinoprostone can be placed in either the cervix or the posterior fornix. Prepidil is a formulation and delivery system of dinoprostone that delivers a dose of 0.5 mg into the cervix, while Cervidil consists of the drug embedded in a plastic matrix. The matrix is designed to deliver a dose of 0.3 mg per hour for 12 hours. 

Intravenous use of ethanol, while once widely employed to inhibit premature labor, is now of historical interest only. Ethanol inhibits oxytocin release from the pituitary and thus indirectly decreases myometrial contractility. Today, pz-adrenomimetics and magnesium sulfate have replaced ethanol for parenteral tocolysis. 

With the increasing evidence that oxytocin is important in human labor, investigators are studying oxytocin antagonists for the treatment of preterm labor. Atosiban is an analogue of oxytocin that is modified at positions 1, 2, 4, and 8. It is a competitive inhibitor of oxytocin binding. Early studies have demonstrated that this drug does decrease and stop uterine contractions. Atosiban is not available for use in the United States. 

B. Indications and use Oxytocin is widely used for induction and augmentation of labor. It is also indicated for the control of postpartum uterine bleeding and as adjunctive therapy in the management... 

---