Acute Changes in Fetal Heart Rate Tracing: When It Becomes an Emergency
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2-1
PowerPoint Discussion of a Variety of Fetal Heart Rate Tracings
Continuous electronic fetal heart rate (FHR) monitoring is widely used to monitor all pregnant women with high-risk medical or obstetric conditions, as well as most pregnant women undergoing labor and delivery. The objectives of FHR monitoring during labor are early detection of changes in FHR baseline and patterns in order to identify certain categories that are predictive of fetal hypoxia and acidosis ( Table 2-1 ). Once these changes are identified, the next step is for the medical provider to decide on which ones require careful observation and which FHR require immediate delivery.
Table 2-1
Objectives of Fetal Monitoring in Labor
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Identify fetal heart rate patterns associated with asphyxia
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Ischemia (▾) tissue perfusion
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Hypoxemia (▾ [O 2 ] in blood)
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Hypoxia (▾ [O 2 ] in tissue) → acidosis
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Asphyxia (hypoxia and metabolic acidosis)
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Organ injury
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Cerebral insufficiency
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Cerebral palsy
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Fetal death
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Allow obstetric interventions to avert adverse outcome
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Medical
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Instrumental vaginal delivery
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Cesarean section
Guidelines have been published by the National Institute of Child Health and Human Development (NICHD) working group for definitions, interpretation, and management recommendations for various categories of FHR tracings. The research group defined three categories as either normal (Category I), indeterminate (Category II), and abnormal (Category III). These definitions are listed in Table 2-2 (Category I) and Table 2-3 (Category III). Category II is defined as any pattern not included in Category I or III. An example of Category I FHR patterns is seen in Figure 2-1 , of Category II in Figure 2-2 , and of Category III in Figure 2-3 . The same group also recommended abolishing the term hyperstimulation for uterine activity and suggested using the term uterine tachysystole ( Table 2-4 ). The definition of baseline variability is described in Table 2-5 . Minimal or absent variability can be due to medications that depress the fetal central nervous system, hypoxia, or acidosis (maternal or fetal). The presence or absence of FHR accelerations was not considered important to define the three categories.
Table 2-2
Category I FHR Pattern (Normal)
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Baseline rate, 100-160 bpm
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Moderate variability (6-25 bpm)
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Absent variable and late decelerations
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Absence or presence of early accelerations/decelerations
Table 2-3
Category III FHR Pattern (Abnormal)
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Definition
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Absent variability (zero) plus either
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Recurrent late decelerations (20 min)
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Recurrent variable decelerations (20 min)
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Bradycardia (<100 bpm for ≥10 min)
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Sinusoidal pattern
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Smooth, undulating, sine wave
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Cycle frequency 3-5/min
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Persists ≥20 minutes
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Treatment
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Immediate delivery
Figure 2-1
Fetal heart rate tracing showing normal baseline and moderate variability (Category I).
Figure 2-2
Fetal heart rate tracing revealing moderate variability and late deceleration (Category II).
Figure 2-3
Absent variability and recurrent late decelerations (Category III).
Table 2-4
Uterine Tachysystole
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Definition
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More than 5 contractions in 10 minutes
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Averaged over 30-minute window
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With/without FHR decelerations
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Treatment
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Discontinue oxytocin or prostaglandins
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Give oxygen by mask
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Give terbutaline 0.25 mg IV
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Consider delivery if associated with abnormal FHR pattern and no response to therapy
Table 2-5
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