What are indications for amniotomy? identify one (1) post-procedure intervention.

Amniotomy Hook

1.

The patient should attempt to relax in the recumbent position with feet together and hips externally rotated (i.e., frog-legged) or in stirrups. Observe universal blood and body fluid precautions when performing this procedure. Record the fetal heart rate before, during, and after amniotomy. Perform a cervical examination to confirm that the membranes are intact, the cervix is at least 3 cm dilated, and the head is well applied. The presence of an umbilical cord should be excluded.

Introduce the second and third digits (index and middle fingers) of the nondominant hand, palmar side up, into the vagina. Insert the fingertips past the cervical lip, into the uterus, and against the membranes. Make sure that the fingers are placed against the membranes rather than over a thin cervical lip.

Grasp the amniotomy hook with your dominant hand. Introduce the tip into the vagina and into a position between the two fingers on the nondominant hand already applied against the membranes (Fig. 148.3). The hook should be pointed downward (away from the membranes). Ask an assistant to apply fundal and suprapubic pressure to reduce the risk of cord prolapse. This maneuver may also increase the amount of fluid bulging between the membranes and the head. This bulge mimics a bag, hence the description of the mother’s “bag of water.” Avoid compressing the membranes too tightly against the infant’s head with the nondominant hand; this may make it more difficult to hook the bag.

Invert the hook upward (i.e., rotate it 180 degrees), apply pressure to the bag with the hook, and rupture the bag with a single motion of the sharp hook. If successful, amniotic fluid should run from the vagina. If no fluid is seen, repeat this step two or three times until fluid is noted to flow from the vagina. If these attempts are unsuccessful, and the bag is still palpable, relax the fingertips away from the membranes and move them slightly. This will allow you to hook the bag from a different direction. Make sure the fingers of your nondominant hand are against the membranes (and not the cervix) and again attempt to rupture the bag with a single motion of the hook. The bag may be quite slippery, so redirecting several times may be required before the amniotomy is successful. Apply varying amounts of pressure against the membranes with the nondominant hand with each attempt. If unsuccessful at this point, request a new hook because the hook may be defective. If there is little fluid palpable (no bag) at the beginning of the procedure, instead of rupturing the membranes or “breaking the bag of water” with the hook, the clinician should attempt to grasp and tear the membranes with the hook. If successful, even though fluid was not apparent as a bag before amniotomy, it may still run out of the vagina. Without a full bag, the sensation of performing amniotomy is quite different; the clinician may have the sensation of merely scratching the fetal scalp with the hook. As long as the clinician is sure that the presentation is vertex and only gentle attempts are made at hooking the bag, the risk of actually scratching or lacerating the infant’s scalp is small.

After successful amniotomy, remove the hook. Note the amount of fluid that drains. If very little fluid is seen, no prior ultrasonography was performed, and the membranes were previously thought to be intact, the diagnosis of oligohydramnios should be considered. If so, be prepared for additional resuscitative needs at delivery, especially in a growth-restricted fetus.

Maintain the fingers of the nondominant hand against the fetal head as fluid is allowed to leak out, noting the color of the fluid (clear or meconium stained). Be sure to confirm that the umbilical cord has not prolapsed.

Remove the fingers and observe the fetal monitor for any nonreassuring signs, such as fetal bradycardia or tachycardia. Prepare to respond (e.g., administer oxygen to the mother, roll her on her side, administer intravenous fluid) if an abnormal fetal heart rate persists.

Artificial Rupture of Membranes

Amniotomy, or artificial rupture of membranes (AROM), can be performed safely if the presenting part is well applied to the cervix. Numerous studies investigated this method as an adjunct to other methods such as oxytocin and prostaglandins, but only two compared the use of amniotomy alone with other methods. Late amniotomy seems to be safer and more effective than early amniotomy.25 A systematic review of studies on amniotomy alone did not find sufficient evidence to support this method.26 Risks include prolonged rupture of membranes with higher rates of infection and cord prolapse.

Amniotomy

The intact amnion serves as the vessel that contains the amniotic fluid and helps protect the uterine contents from the microbial flora of the vagina. The amniotic fluid provides mechanical protection for the fetus and umbilical cord and allows growth and movement.

In the absence of intervention, the membranes generally rupture at the onset of labor or near full cervical dilation. If the membranes are intact, should they be artificially ruptured during the course of labor? If so, when? Because there is concern about infection once the membranes are ruptured, the performance of an amniotomy commits the mother to delivery. The traditional thought was that amniotomy should not be done early in the labor course. However, newer data suggest early amniotomy (i.e., amniotomy at cervical dilation less than 4 cm or soon after cervical ripening with Foley balloon) decreases the time to complete dilation and vaginal delivery, especially in nulliparous women, without an increase in adverse perinatal outcomes.17,18

Advantages of amniotomy during the first stage of labor are that (1) the ruptured membranes permit the placement of a fetal electrocardiographic electrode, which can provide more consistent information than external FHR monitoring; (2) the amniotic fluid can be inspected for the presence or absence of meconium; and (3) amniotomy shortens time to delivery.17,18 Disadvantages of amniotomy during the first stage of labor are that it may result in increased scalp edema (i.e., caput succedaneum, which has no clinical significance) and that there may be a greater likelihood of variable decelerations of the FHR. If there is a nonvertex presentation or the vertex is high in the pelvis and not well applied to the cervix, amniotomy is deferred to decrease the risk for prolapse of the umbilical cord.

B. Stage One Management

1.

Amniotomy

Amniotomy as an intervention has been evaluated in a Cochrane review22 and noted to decrease the incidence of dystocia (OR, 0.33; NNT = 9) and the use of oxytocin in labor (OR, 0.79; NNT = 25) but has also been associated with a near-statistical increase in the rate of cesarean delivery (OR, 1.26; NNH = 85). The decrease in dystocia was most pronounced in patients dilated 3 cm or more at the time of amniotomy.23 Although the incidence of cord prolapse has not been reported to be increased in the trials of amniotomy, it is reasonable to balance its benefit in decreasing oxytocin use and dystocia with the possible risk for increasing cesarean delivery rate in choosing to use this intervention.

Oxytocin augmentation

Table 15-1 compares current low-, intermediate-, and high-dose oxytocin protocols. The low- and high-dose protocols are those that the American College of Obstetricians and Gynecologists (ACOG) suggested in their technical bulletin24; the high-dose regimen is similar to the standard oxytocin protocol used at the National Maternity Hospital in Dublin. Two trials of low-versus high-dose oxytocin (Pitocin) support the benefit of a high dose in the setting of induction. In the larger study, Satin and co-workers25 show that high-dose oxytocin (Pitocin; starting dose 6 mU/min, increasing by 6 mU/min every 20 minutes) was associated with a 9% cesarean rate, a spontaneous delivery rate of 75%, and a forceps delivery rate of 12% in 944 patients. In the low-dose group of 732 patients, the cesarean rate was 12%, the spontaneous delivery rate was 68%, and the forceps delivery rate was 16%. Although another study by Xenakis and colleagues26 was smaller, it revealed a cesarean rate of 10.4% in the high-dose group (n = 154) and of 25.7% in the low-dose group (n = 156). Both studies showed slightly greater rates of hyperstimulation in the high-dose groups, but equivalent Apgar scores and NICU admission rates. Based on these data, high-dose Pitocin appears to offer advantages in the setting of augmentation of labor. Of note is that the ACOG also states that during augmentation with oxytocin, fetal well-being “should be assessed electronically or by auscultation and recorded every 15 minutes during the first stage of labor and every 5 minutes during the second stage of labor.”24

Fetal heart rate monitoring

As discussed in Chapter 14, Section E, use of continuous EFM in low-risk populations is associated with an increased incidence of dystocia and cesarean section. Unless there are specific indications for continuous monitoring, intermittent auscultation should be encouraged for all women in labor.

Monitoring the progress of labor

Most authorities consider active-phase labor arrest to occur when the cervix has not dilated despite 2 hours of active labor. This 2-hour “magic number” may indeed need revision, based on a study of active-phase labor arrest. Rouse and colleagues27 treated 542 women diagnosed with arrest (cervix at least 4 cm dilated with less than 1 cm of change in 2 hours) with oxytocin using a goal of obtaining at least 200 Montevideo units for at least 4 hours before considering cesarean delivery. Ninety-seven percent of parous women and 88% of nulliparas delivered vaginally (overall vaginal delivery rate, 92%). In this population, the cesarean section rate would have been 26% if all patients had been operatively delivered when active-phase arrest was diagnosed. Based on the use of the 4-hour protocol, the overall cesarean section rate was 8%. In this population, the epidural rate was 96% in nulliparas and 89% in primiparas; patients were delivered by cesarean for failure to progress after the 4 hours of oxytocin, for nonvertex presentation, or for nonreassuring fetal heart tones.27

Amniotomy

Artificial rupture of membranes may be used as a labor induction method, particularly when a cervix is favorable. Data are lacking to allow any recommendations about amnionotomy alone as a method for labor induction, especially in the setting of an unfavorable cervix. However, there are data regarding amniotomy timing during labor induction when other agents such as oxytocin are already being used. A randomized trial by Macones and colleagues found that early amniotomy (defined as <4 cm) in nulliparous women undergoing induction resulted in a shortened time to delivery, decreasing it by approximately 2 hours. It also increased the proportion of women who delivered within 24 hours (68 % vs. 56%). There was no increase noted in complications with early amniotomy.112

Artificial Rupture of Membranes

Artificial rupture of the membranes (AROM), amniotomy, is performed when the cervix is partially dilated and effaced, and with the fetus in a vertex presentation with the head well applied to the cervix to avoid prolapse of the umbilical cord (or other presenting part). Fetal monitoring accompanies the procedure, as does evaluation of the color of the amniotic fluid to detect for the presence of meconium staining—a possible indication of fetal distress. A Cochrane review identified two trials comprising 50 and 260 women, respectively, that were considered eligible for inclusion in the review of amniotomy alone for labor induction. Conclusions were unable to be drawn on the use of amniotomy alone vs. no intervention, nor amniotomy alone vs. oxytocin alone. When compared with single-dose application of vaginal prostaglandins in women with a favorable cervix in a single center trial, a higher rate of oxytocin augmentation was required in the amniotomy alone group (44% compared with 15%). Combined use of amniotomy and intravenous oxytocin is more effective than amniotomy alone. Limited data suggest that the efficacy of oxytocin plus amniotomy is similar to that of prostaglandins alone.14 Amniotomy is associated with an increase in caesarean section rate. With regard to neonatal outcomes, fewer babies are born with Apgar scores of less than seven, but no statistically or clinically significant differences have been observed in other measures of neonatal morbidity, such as umbilical artery acid-base disturbances and admission to intensive care units.15 Risks of amniotomy include intrauterine infection, umbilical cord prolapse, and disruption of an occult placenta previa or vasa previa with subsequent maternal hemorrhage. Serious complications, however, are rare.12

Overview

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Amniotic fluid going to central circulation

There are three necessary conditions:

Amniotomy (breach in the barrier between the intact fetal membranes that isolate amniotic fluid from the maternal circulation)

Laceration of endocervical or uterine vessels

Traditionally it was thought that a pressure gradient (intrauterine pressure > CVP or uterine venous pressure) was needed, but the presence of an electrochemical gradient can provide the means for mediators of AFE to inflict damage

Immunological factors may also be involved as complement activation may play a role in the pathophysiology of AFE

ICD9-CM: 673.1

Oxytocin

Oxytocin is the most common induction agent used worldwide. It is used alone, in combination with amniotomy, or following cervical ripening with other pharmacological or nonpharmacological methods. Oxytocin is a synthetic analog of the natural labor hormone by the same name. It binds to oxytocin receptors in the uterine myometrium, increases intracellular calcium, and stimulates uterine contractions. A Cochrane review of more than 61 studies concluded that it is safe and effective.38 A black box warning placed on the drug by the FDA states that oxytocin is not to be used for elective labor induction.

Clinical Presentation

Before the wide use of transvaginal ultrasound (US), the classic presentation of vasa previa included either spontaneous vessel rupture or rupture at amniotomy with vaginal bleeding causing fetal shock or death.6 If a vasa previa has not been diagnosed or suspected prenatally, it should be considered when vaginal bleeding occurs after membrane rupture and results in fetal heart rate abnormalities, particularly a sinusoidal pattern.7

With the common use of transvaginal US, it is more often diagnosed during the middle of the second trimester. These cases may resolve over time, allowing for vaginal delivery at term.