19.2 Medical Interventions During Labor

Role of Oxytocin in Uterine Contractions

The physiologic influences on uterine contractions are multifactorial. Research has yet to determine the exact biochemical substances that initiate labor; however, once labor is initiated, maternal oxytocin is released in pulses, causing the involuntary activation of uterine smooth muscle fibers. While most patients have adequate contractions that allow for the progression of labor, some may have contractions that are inadequate. In these cases, labor augmentation with intravenous oxytocin is used. The nurse titrates the oxytocin to induce adequate contractions for progression of labor while allowing for uterine relaxation between contractions and fetal oxygenation.

Oxytocin binds to receptors in the uterine muscle to stimulate contractions. The response to oxytocin depends on many factors (Uvnäs-Moberg, 2023). If a pregnancy is not yet considered term, the uterus has fewer oxytocin receptors and does not respond to intravenous oxytocin in the same way as a term uterus. Other factors affecting oxytocin response are individual biological differences, length of labor, cervical status, and preexisting uterine activity.

Insufficient Contraction Frequency and Strength

Adequate contraction patterns are defined as uterine contractions with enough duration, strength, and frequency to cause progressive cervical dilation and fetal descent (Rosen & Yogev, 2023). Insufficient contraction patterns lead to insufficient cervical dilation, fetal descent, and labor dystocia. The frequency of uterine contractions is determined by measuring the minutes from the beginning of one contraction to the beginning of the next contraction. Coupling or tripling of contractions can occur and is most often associated with dysfunctional labor, cephalopelvic disproportion, or the occiput posterior position. Figure 19.7 shows a monitor tracing that indicates uterine contraction coupling. The nurse can estimate uterine contraction strength using palpation or can calculate exact uterine contraction strength in Montevideo units using an intrauterine pressure catheter. The nurse uses these techniques to help determine adequacy of the contractions. For a full discussion of Montevideo units, see Chapter 16 Electronic Fetal and Uterine Contraction Monitoring.

Figure 19.7 Coupling of Uterine Contractions Uterine contraction coupling is seen with an occiput posterior presentation, labor dystocia, or cephalopelvic disproportion. This type of contraction pattern can be inadequate for labor progression. (attribution: Copyright Rice University, OpenStax, under CC BY 4.0 license)

Uterine Tachysystole

More than five contractions occurring in 10 minutes averaged over 30 minutes is called uterine tachysystole. Uterine tachysystole does not allow enough time between contractions for placental perfusion and fetal reoxygenation. If allowed to continue, this can lead to fetal hypoxia or uterine rupture. Figure 19.8 illustrates uterine tachysystole on a fetal monitor tracing. The typical uterine contraction pattern is three to five contractions in 10 minutes. Common causes of tachysystole are administration of cervical ripening and inductive medications. Other causes can be maternal dehydration, preeclampsia, placental abruption, and chorioamnionitis (Leathersich et al., 2018). Additionally, partial placental abruption allows blood to seep into the uterine muscle, causing uterine irritability and eventual tachysystole (Sukumaran et al., 2021). Uterine tachysystole can lead to fetal hypoxia because of the diminished blood flow while the uterus is contracting.

Figure 19.8 Uterine Tachysystole The monitor tracing shows contractions with little rest between them and rising uterine baseline. (attribution: Copyright Rice University, OpenStax, under CC BY 4.0 license)

Clinical Safety and Procedures (QSEN)

Management of Uterine Tachysystole

Uterine tachysystole is defined as more than five contractions in 10 minutes averaged over 30 minutes. When administering oxytocin for induction or augmentation of labor, uterine tachysystole is a risk factor. The following interventions should be used when uterine tachysystole is diagnosed.

For uterine tachysystole with nonreassuring fetal heart rate pattern:

1. Discontinue oxytocin.
2. Turn laboring patient to lateral position.
3. Administer 500 mL intravenous (IV) bolus (unless contraindicated).
4. Administer 0.25 mg terbutaline subcutaneously (SQ) (when ordered).

For uterine tachysystole with reassuring fetal heart rate pattern:

1. Reposition laboring patient (left or right lateral position).
2. Administer 500 mL IV bolus (unless fluid restricted).
3. If uterine activity does not return to the expected normal pattern within 10 minutes, follow institution protocol for decreasing or discontinuing intravenous oxytocin.
4. Have terbutaline 0.25 mg SQ readily available.

(Lyndon & Wisner, 2022)

Augmentation of Labor

The enhancement of uterine contractions that have failed to cause cervical dilation, effacement, or fetal descent is called labor augmentation. Amniotomy is often used to augment labor. The fetal head must be engaged in the pelvis prior to an amniotomy to reduce the risk of a prolapsed cord. ACOG (2019c) found that amniotomy alone during normal, spontaneous labor did not decrease the time to delivery or affect the incidence of cesarean birth. When amniotomy was performed for labor augmentation in combination with oxytocin administration, labor was shown to be expedited by 1 to 1.5 hours. Oxytocin alone is another method of labor augmentation. The nurse starts oxytocin and increases or decreases the rate according to the uterine contraction pattern, fetal tolerability to the contractions, and health-care provider orders. Table 19.2 lists the indications and contraindications for augmentation of labor.

The goal of augmentation with intravenous oxytocin is to produce uterine contractions that are strong and frequent enough to cause cervical change while also allowing for sufficient fetal oxygenation. Oxytocin is administered using an infusion pump and infused in milliunits per minute. Typically, oxytocin infusion begins at 1 to 2 milliunits per minute and increases 1 to 2 milliunits per minute every 15 to 30 minutes until an adequate contraction pattern is obtained. The typical time for the uterus to respond to the initiation of the infusion is 3 to 5 minutes. When an oxytocin infusion is stopped, the amount of oxytocin in the plasma rapidly declines due to the drug’s 3- to 5-minute half-life (U.S. Food and Drug Administration (USFDA), n.d.). The maximum dose of oxytocin is usually determined by hospital protocols or individual health-care providers. The nurse discontinues the oxytocin infusion in the presence of tachysystole, nonreassuring fetal heart rate pattern, and suspected uterine abruption or rupture, and notifies the health-care provider immediately.

Adverse effects of oxytocin use include fetal distress, water intoxication, and, in rare situations, uterine rupture and urinary retention. Fetal distress occurs when contraction frequency does not allow for adequate fetal recovery and oxygenation. Water intoxication can occur because oxytocin has an antidiuretic action. Uterine rupture is rare in an unscarred uterus. The uterus that has been scarred from a cesarean birth or myomectomy is at higher risk of rupture with oxytocin use.

Induction of Labor

The stimulation of uterine contractions prior to the spontaneous onset of labor is induction of labor. When determining the appropriateness of labor induction, the benefits to the pregnant person or fetus must outweigh the risk of continuing the pregnancy. Table 19.3 reviews the criteria, indications, and contraindications of labor induction.

Prior to labor induction, the cervix is evaluated to determine if it is ready for labor. This is called a “ripe” or “favorable” cervix. The Bishop score is a tool used to determine if the cervix is favorable. Table 19.4 presents the components of the Bishop score. The higher the Bishop score, the more favorable the cervix. A labor induction is more successful with a higher Bishop score. If the score is low, the nurse anticipates using a cervical ripening agent to prepare the cervix for labor (Kuba et al., 2023).

Cervical ripening agents can be prostaglandins inserted near the cervix, oral prostaglandins, or mechanical devices such as a Foley or double balloon catheter that manually softens and dilates the cervix. These ripening agents are used prior to induction medications. Misoprostol (Cytotec) and dinoprostone (Cervidil) absorb systemically. If tachysystole occurs, dinoprostone can be removed from the vagina. Misoprostol cannot be removed from the patient’s system; therefore, a tocolytic can be administered if tachysystole occurs.

When the health-care provider inserts a Foley catheter for mechanical cervical ripening, a catheter with a 25- to 50-milliliter balloon is inserted through the cervical canal. The balloon is inflated with sterile saline or water. The balloon puts pressure on the internal cervical os. The balloon is usually in place for 8 to 12 hours. When using a double balloon catheter with two balloons, the catheter is inserted through the cervical canal. The balloon at the internal cervical os is inflated with 30 to 60 milliliters of sterile saline or water. The balloon at the outer cervical os is then inflated. The catheter remains in place between 12 and 24 hours. The role of the nurse is to educate the laboring person and assist the health-care provider during insertion. Figure 19.9 shows these two mechanical cervical ripening agents.

Figure 19.9 Foley Catheter and Double Balloon Catheter for Mechanical Cervical Ripening (a) The Foley catheter is inserted into the cervical canal, and the bulb is inflated with normal saline or sterile water. (b) The double balloon catheter is inserted into the cervical canal with one bulb inflated on the internal cervical os and the other inflated on the external cervical os. (attribution: Copyright Rice University, OpenStax, under CC BY 4.0 license)

Oxytocin is the most commonly used medication for labor induction. When oxytocin is administered for the induction of labor, the nurse prepares the pregnant person by explaining the purpose of oxytocin use.

• Oxytocin is mixed in different combinations. The nurse must be aware of the amount of oxytocin per milliliter of fluid.
• Oxytocin is infused via a pump.
• Starting dose is usually 0.5 to 2 milliunits/minute.
• The dose is increased according to institution protocol, most frequently by 1 to 2 milliunits/minute every 30 minutes until an adequate contraction pattern is obtained.
• The maximum oxytocin dose is usually determined by the health-care provider or hospital protocol.

Amnioinfusion

The process of replacing amniotic fluid by adding fluid back to the uterus is amnioinfusion. The technique is done through the port on the intrauterine pressure catheter. A bag of normal saline or lactated Ringer solution is connected to the catheter port and infused as a bolus or at a continuous rate. Indications for amnioinfusion are umbilical cord compression. The extra fluid allows more space for the umbilical cord and can relieve cord compression. Prelabor rupture of membranes can cause umbilical cord compression or malposition of the fetal head.

Amnioinfusion can help lower the risk for cesarean birth or vacuum or forceps use; can dilute meconium; and can improve Apgar scores (Narbhavi et al., 2020). Amnioinfusion is contraindicated during fetal distress, active genital herpes infection, placenta previa, placental abruption, or fetal malpresentation. Complications can occur during amnioinfusion. The most common complications are chorioamnionitis, umbilical cord prolapse, prolonged labor, and perforated uterus. The nurse will monitor the pressure of the uterus during the amnioinfusion to avoid overdistention.