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Guidance to help you assess fetal heart rate tracings.

The majority of women in labor in the United States undergo continuous intrapartum fetal heart rate monitoring. However, the pervasive use of electronic fetal monitoring in obstetric practice has been challenging because of a lack of standardized nomenclature for heart rate assessment and clear guidance about how to interpret and manage various types of tracings.

The issue of nomenclature was a main focus of a 2008 workshop sponsored by the American College of Obstetricians and Gynecologists (ACOG), the Eunice Kennedy Shriver National Institute of Child Health and Human Development, and the Society for Maternal-Fetal Medicine. Workshop participants, myself included, reaffirmed nomenclature for baseline fetal heart rate (FHR) and FHR variability, accelerations, and decelerations. We also recommended new terminology and nomenclature for the description of uterine contractions. We were driven by the need to "speak the same language"--that is, to agree on definitions, lessen ambiguity and allow for a more evidence-based approach to the management of fetal compromise during labor.

In this light, the workshop also recommended adoption of a three-tier system for categorizing FHR patterns. Under this system, Category I FHR tracings are normal and not associated with fetal acidemia. Category II FHR tracings are indeterminate, and Category III FHR tracings are abnormal, or predictive of abnormal fetal acid-based status (Obstet. Gynecol. 2008;112:661-6).

The recommended adoption of this three-tiered classification system was a significant outcome of the workshop and a useful first step in bringing more clarity and meaning to challenges of electronic fetal monitoring.

There was a problem, however: There are very few tracings that do not fall into Category II. Indeed, a growing number of studies have fraction of all FHR tracings indicated that a significant encountered in clinical care--as many as 85% of tracings, it is believed--are of an "indeterminate" nature. Thus, a major task after the 2008 workshop became one of digging more deeply into the Category II tracings to give practicing physicians more meaningful guidance on how to manage this diverse spectrum of abnormal FHR patterns.

The AGOG Practice Bulletin issued in 2010 on Management of Intrapartum Fetal Heart Rate Tracings" (No. 116) delves into the challenging issue of Category II FHR tracings. It essentially addresses the question, how does one manage the woman who has variable decelerations?

Variable Decelerations

Although intermittent variable decelerations (those that occur with less than 50% of contractions) most often do not require any treatment and are associated with normal perinatal outcomes, recurrent variable decelerations (those occurring with 50% or more of contractions) can be more indicative of impending fetal acidemia.

The evidence is fairly strong that recurrent variable decelerations result from umbilical cord compression. Changing maternal position is a good first step to alleviate some of that compression. Amnioinfusion, that is, the infusion of a solution into the uterine cavity to cushion the umbilical cord--also may be used in managing umbilical cord compression.

A meta-analysis reviewed and reprinted this year in the Cochrane Database of Systematic Reviews concluded that the use of amnioinfusion for "potential or suspected umbilical cord compression" may reduce the occurrence of variable FHR decelerations, improve short-term measures of neonatal outcome, reduce maternal postpartum endometritis, and lower the rate of cesarean delivery (Cochrane Database Syst. Rev. 2012 Jan. 18;1:CD000013).

One important overarching principle is that in FHR tracings with recurrent variable decelerations--as in other types of Category II tracings--the presence of FHR accelerations (either spontaneous or induced) or FHR variability that is good ("moderate" FHR variability) is significantly predictive of a fetus that is not acidemic.

Recurrent variable decelerations should, of course, be evaluated for frequency, depth, and duration; uterine contraction pattern; and other FHR characteristics. If variable decelerations get deeper and/or last for longer periods of time, one has to be more concerned than if decelerations are not lasting as long, or if FHR is not dropping as much.

Other Category II Tracings

* Recurrent Late Decelerations. These patterns are believed to reflect uteroplacental insufficiency, which is usually caused by uterine tachysystole, maternal hypoxia, or maternal hypotension, the latter of which often occurs after the administration of regional anesthesia. Measures to improve perfusion to the placenta include the administration of intravenous fluid boluses, maternal oxygen administration, and steps to reduce uterine activity when the uterus is contracting too frequently. One important initial measure is to check the blood pressure, and if it is low (likely due to regional anesthesia), to work with the anesthesiologist on appropriate medical management of hypotension.

As is the case with variable recurrent decelerations, the presence of accelerations or moderate FHR variability, or both, provides reassurance that the baby is doing well at that point. Evaluating for the presence of these factors is important and can be most helpful with recurrent late decelerations, as these patterns in general are poorly predictive for acidemia.

If late decelerations continue in the setting of minimal FHR variability and absent accelerations, despite intrauterine resuscitation efforts, the presence of fetal acidemia should be considered and the potential need for expedited delivery should be evaluated.

* Fetal Tachycardia. Intrapartum fetal tachycardia, defined as a baseline heart rate greater than 160 beats/min for at least 10 minutes, is a fairly common occurrence in labor. When the FHR is extremely high--greater than 200 beats/min--one should consider fetal tachyarrhythmias. These are uncommon, and it is somewhat unlikely for them to occur for the first time during labor (they are more commonly identified antepartum).

When the FHR is high but in the range of approximately 160-180 beats/min, evaluation for chorioamnionitis and other maternal infections is important. If a fever is present, broad-spectrum antibiotics should be administered.

Again, even in the case of fetal tachycardia, the presence of minimal variability and/or accelerations tells us that the baby is probably not acidemic.

* Bradycardia, Prolonged Decelerations. Intrapartum bradycardia and prolonged decelerations differ mainly in their duration. The patterns are similarly managed since, as the practice bulletin says, clinical intervention is often indicated before a distinction between the two can be made.

In either case, we need to be concerned about the possibility of maternal hypotension (for example, post epidural), umbilical cord prolapse or occlusion, placental abruption, rapid fetal descent, tachysystole, or uterine rupture. Essentially, we must evaluate all these potential causes by performing a vaginal exam to determine whether the baby's head has descended quickly or whether the umbilical cord has fallen ahead of the baby, for example, and by checking the mother's blood pressure. Significant bleeding would signal placental abruption. And, in the case of significant bradycardia, uterine rupture becomes a major concern, especially in women with a prior cesarean.

Management is directed at the underlying cause and at resuscitating and supporting the baby with the use of fluid, oxygen, and other targeted measures.

Category III: Timing of Delivery

As part of its framework for managing FHR patterns based on the three-tiered categorization, ACOG's 2010 Practice Bulletin also addresses the critical question of the timing of emergent cesarean delivery Category III tracings most often require prompt delivery when intrauterine resuscitation measures are unsuccessful. Multiple studies, however, have called into question the 30-minute decision-to-incision time that historically has been the guiding principle in the setting of abnormal Category III patterns.

In one study published in 2006 involving 2,808 women who had cesarean deliveries for emergency indications including umbilical cord prolapse, placental abruption, and "nonreassuring fetal heart rate pattern," adverse neonatal outcomes were not increased among infants delivered after more than 30 minutes. (Approximately one-third of the emergency cesarean deliveries began more than 30 minutes after the decision to operate was made, and most of these deliveries were for non-reassuring FHR tracings.)

In fact, the vast majority of those delivered after 30 minutes--95%--did not experience a measure of newborn compromise (Obstet. Gynecol. 2006; 108:6-11). Other studies have similarly failed to show any association of increased adverse outcomes with a 30-minute time frame.

Rather than thinking about deliveries within 30 minutes, we should deliver based on timing that best incorporates maternal and fetal risks and benefits, as the practice bulletin states. The bottom line, in other words, is to accomplish delivery both as expeditiously as possible and as safely as possible for the baby and for the mother. There is no single optimal time frame. A mother with morbid obesity and significant anesthesia risk, for instance, may require more stabilization or surgical preparation than a mother without such a high-risk condition.

GEORGE A. MACONES, M.D.

DR. MACONES said he had no relevant financial disclosures.
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Title Annotation:OBSTETRICS
Author:Macones, George A.
Publication:OB GYN News
Date:Nov 1, 2012
Words:1410
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