intrapartum fetal heart rate analysis 2009

Chukwuma I. Onyeije, M.D.Atlanta Perinatal AssociatesClinical Associate ProfessorMorehouse School of Medicine

http://maternalfetalmedicineblog.comhttp://onyeije.net/present

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Case Control Study:

More than 11,000 pregnancies studied.

FHR Characteristics associated with an increased risk of cerebral

palsy

1. Multiple late decelerations2. Decreased beat-to-beat

variability of the heart rate

POSITIVE TEST NEGATIVE TESTCEREBRAL PALSY 21 74NO CEREBRAL PALSY 10770 115511

NELSON, and Colleagues. NEJM; 1996

The impairment of the delivery of oxygen to the brain and vital tissues during the progress of

labor.

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•Hypertensive disorders•Preterm delivery•IUGR

Fetal Heart Rate evaluation has a high rate of false positives

Clinical management based soley on FHR to avoid asphyxia can result in more harm than good.

Many infants with cerebral palsy do not have have clinically apparent intrapartum abnormalities

Is there a way to improve FHR interpretation to improve perinatal outcome?

Macones GA, Hankins GD, Spong CY, Hauth J, Moore T. The 2008 National Institute of Child Health and Human Development workshop report on electronic fetal monitoring: update on definitions, interpretation, and research guidelines. Obstet Gynecol 2008;112:661–6.

Review and update definitions of FHR patterns

Evaluate existing classification systems for FHR

Make recommendations for research priorities

BACKGROUND CLINICAL INFORMATIONNATURE / PRESENCE OF CONTRACTIONS

BASELINE FHRFHR VARIABILITY

PRESENCE OF ACCELERATIONSPRESENCE OF DECELERATIONSCHANGES IN FHR OVERTIME.

Number of contractions in a 10 minute window averaged over a 30

minute window.

FHR: PATIENT A 5 ctx per 10 min 4 ctx per 10 min 6 ctx per 10 min

TOTAL =15 ctx in 30 min

ANSWER: 15 ∕ 3 ═

5 ctx per 10 min

FHR: PATIENT B 2 ctx per 10 min 0 ctx per 10 min 4 ctx per 10 min

TOTAL =6 ctx in 30 min

ANSWER: 6 ∕ 3 ═

2 ctx per 10 min

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ACTIVITY CLASSIFICATION

Contractions per 10 min

Normal Activity Five or Less

TACHYSYSTOLE More than 5

HYPERSTIMULATION No Longer Valid

HYPERCONTRACTILITY No Longer Valid

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DURATION of contractions

INTENSITY of contractions

RELAXATION time between contractions

A normal fetus can withstand the stress of labor without suffering from hypoxia because sufficient oxygen exchange occurs during the interval between contractions.

A fetus whose oxygen supply is marginal cannot tolerate the stress of contractions and will become hypoxic.

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Fetal heart rate Meconium Fetal blood sampling Umbilical cord blood sampling The Apgar scoring system Contraction stress test Ultrasonic assessment Biophysical profile testing

Other Ways to Evaluate a FetusDuring Labor

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Auscultation of the fetal heart:by stethoscope or Doppler probe

Continuous Electronic fetal monitoring

External monitoring Internal monitoring

Macones GA, Hankins GD, Spong CY, Hauth J, Moore T. The 2008 National Institute of Child Health and Human Development workshop report on electronic fetal monitoring: update on definitions, interpretation, and research guidelines. Obstet Gynecol 2008;112:661–6.

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Rate Beats/min

Normal 120-160

Tachycardia >160

Bradycardia <120

Fetal Heart Rate (in beats per minute)

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Baseline variability Short-time variability /beat-to-beat

variability: short-term variability reflects the interval between either successive fetal electrocardiogram signals or

mechanical events of the cardiac cycle Long-term variability :Long-term

variability reflects the frequency and amplitude of change in the baseline rate

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Normal short-time variability fluctuates between 5 and 25 bpm

Variability below 5 bpm is considered to be potentially abnormal

When associated with decelerations a variability of less than 5 beats/minutes usually indicates severe fetal distress

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The normal long-term variability is 3 to 10 cycles per minute.

Variability is physiologically decreased during the state of quiet sleep of the fetus,which usually lasts for about 25 minutes until transition occurs to another state.

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Short-time variability beat-to-beat variability Long-term variability

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No change: The FHR maintains the same characteristics as in the preceding baseline FHR.

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Acceleration: The FHR increases in

response to uterine contractions. this is normal response.

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Deceleration: The FHR decreases in response to uterine contractions. Decelerations may be early, late, variable or mixed. All except early decelerations are abnormal.

Baseline rate 110-160 bpm, Moderate variability, Absence of late, or variable

decelerations, Early decelerations and accelerations

may or may not be present.

Baseline rate Bradycardia WITHOUT absent baseline

variability Tachycardia

Baseline FHR variability Minimal baseline variability Absent baseline variability with no recurrent

decelerations Marked baseline variability

Accelerations Absence of induced accelerations after fetal

stimulation

Periodic or episodic decelerations Recurrent variable decelerations

accompanied by minimal or moderate baseline variability

Prolonged deceleration more than 2 minutes but less than 10 minutes

Recurrent late decelerations with moderate baseline variability

Variable decelerations with other characteristics such as slow return to baseline, overshoots, or “shoulders”

Absent baseline FHR variability and any of the following: Recurrent late decelerations Recurrent variable decelerations Bradycardia

Sinusoidal pattern

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Early deceleration (head compression):

Late deceleration ( uteroplacental insufficiency

Variable deceleration (cord compression)

Combined or mixed patterns Decreased beat-to-beat variability

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Definition: The onset, maximum fall, and recovery of FHR is a mirror image of the onset, peak, and end of the uterine contraction.

Significance: This pattern is seen when engagement of the fetal head has occurred. Early decelerations are not thought to be associated with fetal distress.

Mechanism: The pressure on the fetal head leads to increased intracranial pressure that elicits a vagal response

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Late Decelerations (Uteroplacental Insufficiency)

Definition: ---onset ---maximal ---decrease ---recovery is shifted to the right in relation to the

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Late deceleration (uteroplacental insufficiency)

Significance: The severity is graded by the

magnitude of the decrease and the nadir of the deceleration

Fetal hypoxia and acidosis are more pronounced with severe decelerations

Generally associated with low scalp blood PH values and high base deficits, indicating metabolic acidosis from anaerobic netabolism

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Definition: This pattern has a variable time of onset and a variable form and may be nonrepetitive

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Significance:

caused by umbilical cord compression. The severity is graded by their duration.

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Partial or complete compression of the cord causes a sudden increase in blood pressure in the central circulation of the fetus.

The bradycardia is mediated via baroreceptors Fetal blood gases indicate respiratory acidosis

with a low PH and high CO2. When cord compression has been prolonged, hypoxia is also present, showing a picture of combined respiratory and metabolic acidosis in fetal blood gases

Variable deceletation (cord compression)

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A flat baseline can be the result of several conditions:

Fetal acidosis Quiet sleep state Maternal sedation with drugs

Decreased beat-to beat variability

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A normal FHR pattern on the electronic monitor indicates a greater than 95% probability of fetal well-being

Abnormal patterns may occur, however, in the absence of fetal distress. The false-positive rate (i.e., good Apgar scores and normal fetal-acid-bade status in the presence of abnormal FHR patterns) is as high as 80 %

Electronic fetal monitoring is a screening rather than a diagnostic technique, because of the high false-positive rate

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Clinical circumstance Maternal condition Stage of labor

Clinical Considerations for FHR Interpretation

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A change in maternal position can relieves fetal pressure on the cord

100% oxygen by face mask to the mother

Oxytocic infusion should be discontinued Elevating the presenting part by vaginal

examination Placing the mother in the trendelenburg

position if the pattern is persistent Use tocolytic agent to diminish uterine

activity

What To Do for… Variable Decelerations

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Aminioinfusion can decrease both the frequency and severity of variable decelerations

The benefit of aminioinfusion results in reduced cesarean deliveries for fetal distress and fewer low Apgar scores at birth without apparent maternal or fetal distress

What To Do for… Variable Decelerations

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The safest intervention to deliver the fetus with cord compression is often low or outlet forceps.

When progressive acidosis occurs , as determined by serial scalp blood PH determinations, cesarean section should be performed if vaginal delivery is not imminent

Prolonged deceleration requires immediate intervention (FHR falls to 60 to 90 bpm for more than 2 minutes)

What To Do for… Variable Decelerations

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Need further evaluation because it may be assosiated with fetal acidosis

acoustic stimulation can be used to try to induce FHR-accelerations

A response of greater than 15 bpm lasting at least 15 seconds can ensures the absence of fetal acidosis

The chance of acidosis occurring in the fetus who fails to respond to such stimulation is about 50%

What To Do for… Nonreactive fetal heart rate tracings

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Change the maternal position from supine to left or right lateral

Give oxygen by face mask, this can increase fetal Po2 by 5 mmHg

Stop any oxytocic infusion Inject intravenously a bolus of tocolytic drug to

relieve uterine tetany. Monitor maternal blood pressure Operative delivery should be considered for fetal Operative delivery should be considered for fetal

distress when fetal acidosis is present or when late distress when fetal acidosis is present or when late decelerations are persistent in early labor and the decelerations are persistent in early labor and the cervix is insufficiently dilatedcervix is insufficiently dilated

What To Do for… Late Decelerations

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Prolonged periods of tachycardia are usually associated with elevated maternal temperature or an intrauterine infection, which should be ruled out.

The acid-base status is usually normal In general, fetal tachycardia occurs to

improve placental circulation when the fetus is stressed.

Not a reliable change of the fetal distress

What To Do for… Fetal Tachycardia

There is an unrealistic expectation that a nonreassuring FHR tracing is predictive of cerebral palsy.

The positive predictive value of a nonreassuring pattern to predict cerebral palsy is 0.14%.

Out of 1,000 fetuses with a nonreassuring FHR pattern, only one or two will develop cerebral palsy

The false positive rate of EFM for predicting cerebral palsy is extremely high, at greater than 99%.

Available data suggest that the use of FHR monitoring does not result in a reduction in cerebral palsy

The interpretation of FHR is more consistent when the tracing is normal

In retrospective reviews, the foreknowledge of neonatal outcome alters the reviewer’s impressions of the tracing.

Reinterpretation of the FHR tracing, if neonatal outcome is known, may not be reliable.

MEDICATION EFFECT

Narcotics Decrease in variability Decrease in the frequency of accelerations

Butorphanol (Stadol)

Transient sinusoidal FHR patternSlight increased mean heart rate

Cocaine Decreased long-term variability

MEDICATION EFFECT

Corticosteroids Decrease in FHR variability with beta-methasone but not dexamethasone, Abolishes diurnal fetal rhythm. Increased effect at greater than 29 weeks of gestation

Magnesium sulfate

Decreased short-term variability, Insignificant decrease in FHR.

MEDICATION EFFECT

Terbutaline Increase in baseline FHR Increased incidence of fetal tachycardia

Zidovudine No difference in the FHR