Fetal Assessment during Labor



Fetal Assessment during Labor


Kitty Cashion




Key Terms and Definitions























Web Resources


Additional related content can be found on the companion website at image


evolve.elsevier.com/Lowdermilk/Maternity/



T he ability to assess the fetus by auscultation of the fetal heart was initially described more than 300 years ago. With the advent of the fetoscope and stethoscope after the turn of the twentieth century the listener could hear clearly enough to count the fetal heart rate (FHR). When electronic FHR monitoring made its debut for clinical use in the early 1970s, the anticipation was that its use would result in fewer cases of cerebral palsy and be more sensitive than stethoscopic auscultation in predicting and preventing fetal compromise (Garite, 2007). Consequently, the use of electronic fetal monitoring rapidly expanded. However, the rate of cerebral palsy has risen slightly since that time and is not likely to improve (Gilbert, 2007). Moreover, in 2006 the cesarean birth rate in the United States reached an all-time high of 31.1% (Collard, Diallo, Habinsky, Hentschell, & Vezeau, 2008/2009).


Still, electronic fetal monitoring (EFM) is a useful tool for visualizing FHR patterns on a monitor screen or printed tracing and continues to be the primary mode of intrapartum fetal assessment. Currently in the United States, approximately 85% of women giving birth have continuous EFM during labor, making it the most commonly performed obstetric procedure (American College of Obstetricians and Gynecologists [ACOG], 2009; Tucker, Miller, & Miller, 2009). Pregnant women should be informed about the equipment and procedures used and the risks, benefits, and limitations of intermittent auscultation (IA) and EFM. This chapter discusses the basis for intrapartum fetal monitoring, the types of monitoring, and nursing assessment and management of abnormal fetal status.




Basis for Monitoring image


Fetal Response


Because labor is a period of physiologic stress for the fetus, frequent monitoring of fetal status is part of the nursing care during labor. The fetal oxygen supply must be maintained during labor to prevent fetal compromise and to promote newborn health after birth. The fetal oxygen supply can decrease in several ways:



• Reduction of blood flow through the maternal vessels as a result of maternal hypertension (chronic hypertension, preeclampsia, or gestational hypertension), hypotension (caused by supine maternal position, hemorrhage, or epidural analgesia or anesthesia), or hypovolemia (caused by hemorrhage)


• Reduction of the oxygen content in the maternal blood as a result of hemorrhage or severe anemia


• Alterations in fetal circulation, occurring with compression of the umbilical cord (transient, during uterine contractions [UCs], or prolonged, resulting from cord prolapse), placental separation or complete abruption, or head compression (head compression causes increased intracranial pressure and vagal nerve stimulation with an accompanying decrease in the FHR)


• Reduction in blood flow to the intervillous space in the placenta secondary to uterine hypertonus (generally caused by excessive exogenous oxytocin) or secondary to deterioration of the placental vasculature associated with maternal disorders such as hypertension or diabetes mellitus


Fetal well-being during labor can be measured by the response of the FHR to UCs. A group of fetal monitoring experts have recently recommended that FHR tracings that demonstrate the following characteristics be described as normal (Macones, Hankins, Spong, Hauth, & Moore, 2008):




Evidence-Based Practice


Fetal Monitoring and the Machine that Goes “Beep”






Critically Analyze the Evidence


Electronic fetal heart monitoring (EFM; also known as cardiotocography [CTG]) has become standard procedure in the labor and birth setting for many decades, especially in the United States. The suggestion has been made that such monitoring is not necessary for the low-risk labor patient and may even present a risk of false abnormal readings that lead to high rates of cesarean births.


A meta-analysis of trials measuring fetal outcomes and use of EFM revealed no significant change in Apgar scores for women who had EFM on admission for labor when compared with women who were not monitored on admission. However, a statistically increased risk was noted for cesarean birth in the monitored women (Gourounti & Sandall, 2007).


The National Institute for Health and Clinical Excellence (NICE) issued professional guidelines for intrapartum care that do not recommend EFM for the low-risk laboring patient (NICE, 2007). Instead, the guidelines recommend intermittent auscultation on admission and during labor, using a stethoscope or Doppler. Use of continuous EFM should begin in the presence of meconium, bleeding, abnormal fetal heart rate (<110 bpm or >160 bpm), oxytocin use, or patient request. Similar clinical practice guidelines from the Society of Obstetricians and Gynaecologists of Canada (2007) also recommend intermittent auscultation in the absence of risk factors. EFM should be used for high-risk women, with fetal scalp blood pH testing if abnormal patterns arise. The guidelines do not recommend the routine use of fetal pulse oximetry.


Some question remains about the use of fetal pulse oximetry as an adjunct assessment that might be more reassuring and thus decrease cesarean rates. A Cochrane systematic analysis examined five trials, involving 7424 women, and showed no difference in cesarean rates between women with EFM alone versus women being monitored with EFM and fetal pulse oximetry together (East, Chan, Colditz, & Begg, 2007). However, the reviewers believed that the use of the fetal pulse oximeters may have provided some reassurance, thus buying some additional time for providers to adequately prepare for cesarean birth.



Implications for Practice


EFM is here to stay, but it is only a tool. Women and providers have come to expect the constant feedback, and busy nurses have come to rely on the remote screens as they move from room to room. However, the risks of false alarms, as well as the legal vulnerability of ambiguous patterns, may be contributing to the soaring cesarean rate, which carries its own risks. Continuous monitoring of low risk women restricts patient mobility, which may prolong labor and increase discomfort. In high risk situations, EFM can be valuable for picking up some fetal stress early, but it may also be inaccurate, ambiguous, and cause needless anxiety. Women who expect routine monitoring need explanations about the risks and benefits of continuous monitoring versus intermittent auscultation, and to be given informed choices. The health care team may also need to become more proficient and familiar with auscultation as an assessment tool.



References:



East, C. E., Chan, F. Y., Colditz, P. B., & Begg, L. (2007). Fetal pulse oximetry for fetal assessment in labor. In The Cochrane Database of Systematic Reviews, 2007, Issue 2, CD 004075.


Gourounti, K., Sandall, J. Admission cardiotocography versus intermittent auscultation of fetal heart rate: Effects on neonatal Apgar score, on the rate of caesarean sections and on the rate of instrumental delivery: A systematic review. International Journal of Nursing Studies. 2007; 44(6):1029–1035.


National Institute for Health and Clinical Excellence (NICE), Intrapartal care: Care for healthy women and their babies during childbirth. NICE Clinical Guideline No. 55. NICE, London, 2007. www.nice.org.uk/nicemedia/pdf/IPCNICEGuidance.pdf


Society of Obstetricians and Gynaecologists of Canada (SOGC), Fetal health surveillance: Antepartum and intrapartum consensus guideline. Clinical Practice Guideline No. 197. SOGC, Ottawa, Ontario, Canada, 2007. www.sogc.org/guidelines/documents/gui197CPG0709.pdf



Uterine Activity


Table 11-1 describes normal uterine activity (UA) during labor.




Fetal Compromise


The goals of intrapartum FHR monitoring are to identify and differentiate the normal (reassuring) patterns from the abnormal (nonreassuring) patterns, which can be indicative of fetal compromise. Although the 2008 National Institute of Child Health and Human Development workshop (Macones et al., 2008) and a recent ACOG Practice Bulletin (2009) both recommend use of the terms normal and abnormal to describe FHR tracings, the terms reassuring and nonreassuring are still frequently used clinically.


Abnormal FHR patterns are those associated with fetal hypoxemia, which is a deficiency of oxygen in the arterial blood. If uncorrected, hypoxemia can deteriorate to severe fetal hypoxia, which is an inadequate supply of oxygen at the cellular level. Examples of abnormal FHR patterns include the following (Macones et al., 2008).


Absent baseline FHR variability and any of the following:




Monitoring Techniques image


The ideal method of fetal assessment during labor continues to be debated. When performed at prescribed intervals, especially during and immediately after contractions, IA has been shown to be as valuable as EFM at predicting fetal outcomes (Gilbert, 2007).



Intermittent Auscultation


Intermittent auscultation (IA) involves listening to fetal heart sounds at periodic intervals to assess the FHR. IA of the fetal heart can be performed with a Pinard stethoscope, a Doppler ultrasound device (Fig.11-1, A) an ultrasound stethoscope (Fig. 11-1, B) or a DeLee-Hillis fetoscope (Fig. 11-1, C). The fetoscope is applied to the listener’s forehead because bone conduction amplifies the fetal heart sounds for counting. The Doppler ultrasound device and ultrasound stethoscope transmit ultrahigh-frequency sound waves reflecting movement of the fetal heart and convert these sounds into an electronic signal that can be counted. Box 11-1 describes how to perform IA.



BOX 11-1


Procedure for Intermittent Auscultation of the Fetal Heart Rate




1. Palpate the maternal abdomen to identify fetal presentation and position.


2. Apply ultrasonic gel to the device if using a Doppler ultrasound. Place the listening device over the area of maximal intensity (see Fig. 11-1) and clarity of the fetal heart sounds to obtain the clearest and loudest sound, which is easiest to count. This location will usually be over the fetal back. If using the fetoscope, firm pressure may be needed.


3. Count the maternal radial pulse while listening to the FHR to differentiate it from the fetal rate.


4. Palpate the abdomen for the presence or absence of UA so as to count the FHR between contractions.


5. Count the FHR for 30 to 60 seconds between contractions to identify the auscultated rate, best assessed in the absence of UA.


6. Auscultate the FHR before, during, and after a contraction to identify the FHR during the contraction, as a response to the contraction, and to assess for the absence or presence of increases or decreases in FHR.


7. When distinct discrepancies in the FHR are noted during listening periods, auscultate for a longer period during, after, and between contractions to identify significant changes that may indicate the need for another mode of FHR monitoring


FHR, Fetal heart rate; UA, uterine activity.


Source: Tucker, S. M., Miller, L. A, & Miller, D. A. (2009). Mosby’s pocket guide to fetal monitoring: A multidisciplinary approach (6th ed.). St. Louis: Mosby.



IA is easy to use, inexpensive, and less invasive than EFM. It is often more comfortable for the woman and gives her more freedom of movement. Other care measures, such as ambulation and the use of baths or showers, are easier to carry out when IA is used. On the other hand, IA may be difficult to perform in women who are obese. Because IA is intermittent, significant events may occur during a time when the FHR is not auscultated. Also, IA does not provide a permanent documented visual record of the FHR and cannot be used to assess visual patterns of the FHR variability or periodic changes (Albers, 2007; Tucker et al., 2009). By using IA the nurse can assess the baseline FHR, rhythm, and increases and decreases from baseline. The recommended optimal frequency for IA in low risk women during labor has not been determined (Nageotte & Gilstrap, 2009).



Every effort should be made to use the method of fetal assessment the woman desires, if possible. However, adherence to the frequency guides can make using IA difficult in today’s busy labor and birth units because when used as the primary method of fetal assessment, auscultation requires a 1 : 1 nurse-to-patient staffing ratio. If acuity and census change such that auscultation standards are no longer met, then the nurse must inform the physician or nurse-midwife that continuous EFM will be used until staffing can be arranged to meet the standards.


The woman can become anxious if the examiner cannot readily count the fetal heartbeats. The inexperienced listener often needs time to locate the heartbeat and find the area of maximal intensity. To allay the mother’s concerns, she can be told that the nurse is “finding the spot where the sounds are loudest.” If the examiner cannot locate the fetal heartbeat, assistance should be requested. In some cases, ultrasound can be used to help locate the fetal heartbeat. Seeing the FHR on the ultrasound screen will be reassuring to the mother if locating the best area for auscultation was initially difficult.


When using IA, UA is assessed by palpation. The examiner should keep his or her hand placed over the fundus before, during, and after contractions. The contraction intensity is usually described as mild, moderate, or strong. The contraction duration is measured in seconds, from the beginning to the end of the contraction. The frequency of contractions is measured in minutes, from the beginning of one contraction to the beginning of the next. The examiner should keep his or her hand on the fundus after the contraction is over to evaluate uterine resting tone or relaxation between contractions. Resting tone between contractions is usually described as soft or relaxed.


Accurate and complete documentation of fetal status and UA is especially important when IA and palpation are being used because no paper tracing record or computer storage of these assessments is provided, as is the case with continuous EFM. Labor flow records or computer charting systems that prompt notations of all assessments are useful for ensuring such comprehensive documentation.




Electronic Fetal Monitoring


The purpose of electronic FHR monitoring is the ongoing assessment of fetal oxygenation. The goal is to detect fetal hypoxia and metabolic acidosis during labor so that interventions to resolve the problem can be implemented in a timely manner before permanent damage or death occur (Garite, 2007).


The two modes of EFM include the external mode, which uses external transducers placed on the maternal abdomen to assess FHR and UA, and the internal mode, which uses a spiral electrode applied to the fetal presenting part to assess the FHR and an intrauterine pressure catheter (IUPC) to assess UA and pressure. The differences between the external and internal modes of EFM are summarized in Table 11-2.




External monitoring


Separate transducers are used to monitor the FHR and UCs (Fig. 11-2). The ultrasound transducer works by reflecting high-frequency sound waves off a moving interface: in this case the fetal heart and valves. Reproducing a continuous and precise record of the FHR is sometimes difficult because of artifacts introduced by fetal and maternal movement. The FHR is printed on specially formatted monitor paper. The standard paper speed used in the United States is 3 cm/min. Once the area of maximal intensity of the FHR has been located, conductive gel is applied to the surface of the ultrasound transducer, and the transducer is then positioned over this area and held securely in place using an elastic belt.



The tocotransducer (tocodynamometer) measures UA transabdominally. The device is placed over the uterine fundus and held securely in place using an elastic belt (see Fig. 11-2). UCs or fetal movements depress a pressure-sensitive surface on the side next to the abdomen. The tocotransducer can measure and record the frequency and approximate duration of UCs but not their intensity. This method is especially valuable for measuring UA during the first stage of labor in women with intact membranes or for antepartum testing. Because the tocotransducer of most electronic fetal monitors is designed for assessing UA in the term pregnancy, it may not be sensitive enough to detect preterm UA. When monitoring the woman in preterm labor, remember that the fundus may be located below the level of the umbilicus. The nurse may need to rely on the woman to indicate when UA is occurring and to use palpation as an additional way of assessing contraction frequency and validating the monitor tracing.


The external transducer is easily applied by the nurse, but it must be repositioned as the woman or fetus changes position (see Fig. 11-2, B). The woman is asked to assume a semi-sitting or a lateral position. Use of an external transducer confines the woman to bed. Portable telemetry monitors allow observation of the FHR and UC patterns by means of centrally located electronic display stations. These portable units permit the woman to walk around during electronic monitoring.



Internal monitoring


The technique of continuous internal FHR or UA monitoring allows a more accurate appraisal of fetal well-being during labor than external monitoring because it is not interrupted by fetal or maternal movement or affected by maternal size (Fig. 11-3). For this type of monitoring the membranes must be ruptured and the cervix sufficiently dilated (at least 2-3 cm) to allow placement of the spiral electrode or IUPC or both. Internal and external modes of monitoring may be combined (i.e., internal FHR with external UA or external FHR with internal UA) without difficulty.



Internal monitoring of the FHR is accomplished by attaching a small spiral electrode to the presenting part. For UA to be monitored internally, a solid IUPC is introduced into the uterine cavity. The catheter has a pressure-sensitive tip that measures changes in intrauterine pressure. As the catheter is compressed during a contraction, pressure is placed on the pressure transducer. This pressure is then converted into a pressure reading in millimeters of mercury. The average pressure during a contraction ranges from 50 to 85 mm Hg. The IUPC can measure the frequency, duration, and intensity of UC, as well as uterine resting tone.


The FHR and UA are displayed on the monitor paper, with the FHR in the upper section and UA in the lower section. Fig. 11-4 contrasts the internal and external modes of electronic monitoring. Note that each small square on the monitor paper or screen represents 10 seconds; each larger box of six squares equals 1 minute (when paper is moving through the monitor at the rate of 3 cm/min).




Fetal Heart Rate Patterns image


Characteristic FHR patterns are associated with fetal and maternal physiologic processes and have been identified for many years. Because EFM was introduced into clinical practice before consensus was reached in regard to standardized terminology, however, variations in the description and interpretation of common fetal heart rate patterns were often great. In 1997 the National Institute of Child Health and Human Development (NICHD) published a proposed nomenclature system for EFM interpretation with standardized definitions for FHR monitoring. The NICHD recommendations were not widely incorporated into clinical practice, however, until they were endorsed by the American College of Obstetricians and Gynecologists (ACOG) in 2005. Shortly thereafter, use of the NICHD standard terminology was also endorsed by the Association of Women’s Health, Obstetric, and Neonatal Nurses (AWHONN), and the American College of Nurse-Midwives (ACNM) (Tucker et al., 2009). All three organizations cited concerns regarding patient safety and the need for improved communication among caregivers as reasons for using standard EFM definitions in clinical practice.


In April 2008 the NICHD, ACOG, and the Society for Maternal-Fetal Medicine partnered to sponsor another workshop to revisit the FHR definitions recommended by the NICHD in 1997. The 1997 FHR definitions were reaffirmed at this workshop. In addition, new definitions related to UA were recommended, as well as a three-tier system of FHR pattern interpretation and categorization (Macones et al., 2008). ACOG (2009) has recently published a practice bulletin which supports use of the 2008 NICHD workshop recommendations.



Baseline Fetal Heart Rate


The intrinsic rhythmicity of the fetal heart, the central nervous system (CNS), and the fetal autonomic nervous system control the FHR. An increase in sympathetic response results in acceleration of the FHR, whereas an increase in parasympathetic response produces a slowing of the FHR. A balanced increase of sympathetic and parasympathetic response usually occurs during contractions, with no observable change in the baseline FHR.


The baseline fetal heart rate is the average rate during a 10-minute segment that excludes periodic or episodic changes, periods of marked variability, and segments of the baseline that differ by more than 25 beats/min (Macones et al., 2008). The normal range at term is 110 to 160 beats/min. The baseline rate is documented as a single number, rather than a range (Tucker et al., 2009).



Variability


Variability of the FHR can be described as irregular waves or fluctuations in the baseline FHR of two cycles per minute or greater (Macones, et al., 2008). It is a characteristic of the baseline FHR and does not include accelerations or decelerations of the FHR. Variability is quantified in beats per minute and is measured from the peak to the trough of a single cycle. Four possible categories of variability have been identified: absent, minimal, moderate, and marked (Fig. 11-5). In the past, variability was described as either long term or short term (beat to beat). The NICHD definitions do not distinguish between long- and short-term variability, however, because in actual practice, they are visually determined as a unit (NICHD, 1997).


Oct 8, 2016 | Posted by in NURSING | Comments Off on Fetal Assessment during Labor
Premium Wordpress Themes by UFO Themes