8.fetal surveillance during labor

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Fetal Surveillance During Labor

Du Xue , PHDDepartment of Obstetrics & Gynecology General Hospital of TianJinMedical University

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Fetal Surveillance During Labor----Epidemiology

To be an essential element of good obstetric care because intrapartum hypoxia and acidosis may develop in any pregnancy.

On the basis of prenatal care ----20% to 30% :high risk ----and 50% of perinatal morbidity and mortal

ity occurs in this group ----50% normal

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Mechanisms of fetal distress

Fetal arterial blood oxygen tension is only 25±5mmHg compared with adult values of about 100 mmHg.

The rate of oxygen consumption is twice of the adult per unit weight, and its oxygen reserve is only enough to meet its metabolic needs for 1 to 2 minutes.

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Blood flow from the maternal circulation is momentarily interrupted during a contraction.

Clinical and experimental data indicate that fetal death occurs when 50% or more of transplacental oxygen exchange is interrupted.

Hypoxia can easily occur. 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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Changes under hypoxic conditions

Baroreceptors and chemoreceptors in the central circulation of the fetus influent the FHR by giving rise to contraction-related or periodic FHR changes.

The hypoxia will also result in anaerobic metabolism. Pyruvate and lactic acid accumulate, causing fetal acidosis.

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

Fetal Surveillance During Labor----methods

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Methods of monitorinfetal heart rate Auscultation of the

fetal heart:by stethoscope or Doppler probe

Continuous Electronic fetal monitoring

External monitoring Internal monitoring

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Auscultation of the fetal heart is performed every 15 minutes after a uterine contraction during the first stage of labor.

Auscultation of the fetal heart is performed at least every 5 minutes after a uterine contraction during the second stage of labor.

By continuous electronic fetal monitoring, early recognition of changes in heart rate patterns

that may be associated with such fetal conditions as hypoxia and umbilical cord compression

would serves as a warning and enable the physician to intervene to prevent fetal death in uterus or irreversible brain injury.

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Methods of Electronic Fetal Monitoring External

Noninvasive method Utilizes an ultrasonic transducer to monitor

the fetal heart Utilizes the tocodynamometer (toco) to mo

nitor uterine contraction pattern Application directly impacts results of data

received

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Methods of Electronic Fetal Monitoring Internal Fetal Monitoring

Invasive FHR is monitored via a fetal scalp

electrode (IFSE) Uterine activity is monitored by an

intrauterine pressure catheter (IUPC) A combination of external and

internal fetal monitoring is common practice

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continuous reporting of FHR-UC on a two-channel strip chart recorderby means of a monitor that prints results

----uterine contractions(UC): stress for the fetus ----FHR: alteration in FHR correlates with fetal oxygenation In the clinical setting, internal and external techniques are

often combined ----FHR: by using a scalp electrode for precise heart rate reco

rding ----UC:the external tocotransducer for contractions to avoid

or minimize possible side effects from invasive internal monitoring

Electronic fetal monitoring

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Fetal Heart Rate Patterns

Baseline Assessment

Periodic Fetal Heart Rate Changes related to UC

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Fetal Heart Rate Patterns Basline Assessment

Rate Beats/min

normal 120-160

Tachycardia >160

Bradycardia <120

Fetal Heart Rate (in beats per minute)

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Fetal Heart Rate Patterns Basline Assessment

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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Short-time variability beat-to-beat variability

Long-term variability

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Short-time variability /beat-to beat variability

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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Long-term variability

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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Fetal Heart Rate Patterns Periodic Fetal Heart Rate Changes

Three kinds of responses to uterine contractions

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.

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Types of deceleration Patterns Early deceleration (head compression): Late deceleration ( uteroplacental insuffi

ciency Variable deceleration (cord compression) Combined or mixed patterns Decreased beat-to-beat variability

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Types of deceleration Patterns--1 Early deceleration:(head compression)

Definition: The onset, maximum fall, and recovery that is coincident with 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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Types of deceleration Patterns--2 Late deceleration (uteroplacental insufficiency)

Definition: ---onset ---maximal ---decrease ---recovery that

is shifted to the right in relation to the contraction.

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Types of deceleration Patterns--2 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 usually more pronounced with severe decelerations ---generally associated with low scalp b

lood PH values and high base deficits, indicating metabolic acidosis from anaerobic netabolism

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Types of deceleration Patterns--3 Variable deceletation (cord compression)

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.

Types of deceleration Patterns—3 Variable deceletation (cord compression)

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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

Types of deceleration Patterns—3 Variable deceletation (cord compression)

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A flat baseline can be the result of several conditions:

• Fetal acidosis• Quiet sleep state• Matermal sedation with drugs

Types of deceleration Patterns—4 Decreased beat-to beat variability

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Strategies for intervention--1Attentions

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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the clinical circumstance the maternal condition the stage of labor

Strategies for intervention--1general considerations

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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 examinatio

n placing the mother in the trendelenburg position if t

he pattern is persistent Use tocolytic agent to diminish uterine activity

Strategies for intervention--2 Variable Decelerations

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during the second stage of labor aminioinfusion can decrease both the freque

ncy and severity of variable decelerations The benefit of aminioinfusion results in reduc

ed cesarean deliveries for fetal distress and fewer low Apgar scores at birth without apparent maternal or fetal distress


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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)


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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%

Strategies for intervention--3 Nonreactive fetal heart rate tracing

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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 ut

erine tetany. Monitor maternal blood pressure Operative delivery should be considered for fetal distresOperative delivery should be considered for fetal distres

s when fetal acidosis is present or when late decelerations when fetal acidosis is present or when late decelerations are persistent in early labor and the cervix is insufficiens are persistent in early labor and the cervix is insufficiently dilatedtly dilated

Strategies for intervention--4 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

Strategies for intervention--4 Fetal Tachycardia

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Meconium The presence of meconium in the a

mniotic fluid may be a sign of fetal distress

Classification ----Early passage ----Late passge ----Management

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Meconium ----Early passage occurs any time prior to rupture of the membranes

and is classified as light or heavy, based on its color and viscosity

light meconium: Light meconium is lightly stained yellow or greenish amniotic fluid. It is not associated with poor outcome

Heavy meconium: Heavy meconium is dark green or black and usually thick and tenacious. It is associated with lower 1- and 5- minute Apgar scores and is associated with the risk of meconium aspiration

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Meconium ----Late passge Late passage usually occurs during the sec

ond stage of labor, after clear amniotic fluid has been noted earlier

Late passage, which is most often heavy, is usually associated with some event

----umbilical cord compression ----uterine hypertonus ----fetal distress.

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Meconium ----Management

Amnioinfusion: it can decrease in meconium-related respiratory complications perhaps as a result of the dilutional effect of the infused fluid

Manner: Infuse a bolus of up of up to 800 ml of normal saline at a rat

e of 10-15 ml/minute over a period of 50 to 80 minutes. This is followed by a maintenance dose of 3 ml/minutes until delivery

Overdistention of the uterine cavity can be avoided by maitaining the baseline uterine tone in the normal range and at less than 20mmHg

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Fetal Blood SamplingPH :7.25-7.30

Indication: clinical parameters suggesting fetal distress: ----heavy meconium ----moderate to severely abnomal FHR patterns Fetal Blood PH predicts neonatal outcome 82% of

the time , as measured by the Apgar score. The false-positive nate is about 8%, and the false-

negative about 10%

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Umbilical cord blood sampling

If there have been problems during the delivery or concern with the infant’s condition,obtain an umbilical atery blood specimen for PH and acid-base determination is a syringe flushed with heparin.

If a specimen cannot be obtained from the umbilical artery ,obtain a specimen from an atery on the chorionic surface of the placenta.

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Ultrasonic Doppler velocimetry

For blood flow measurements in umbilical and fetal blood vessels, and percutaneous umbilical bolld sampling (PUBS) have been used antepartum but are generally not feasible methods for labor management.

Attention: Newborn cerebral dysfunction, manifested as seizures and attributable to true birth asphyxia, does not seem to occur unless the Apgar score at 5 minutes is 3 or less, the umbilical artery blood PH is less than 7,and resuscitation is necessary at birth.

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The Apgar scoring system The Apgar score is an excellent tool for asse

ssing the overall status of the newborn soon after birth (1 minute) and after a 5 minutes period of observation.

A normal Apgar score is 7 or greater at 1minute and 9 or 10 at 5 minutes.

Conditions result in low scores include Asphyxia (implies hypoxia of sufficient degree to

cause metabolic acidosis) Prematurity maternal drug administration

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Questions The methods of monitoring the fetal he

art rate Fetal heart rate patterns Classification of meconium Normal level of fetal blood PH

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THANKS FOR YOUR ATTENDANCETHANKS FOR YOUR ATTENDANCE

GOOD LUCKGOOD LUCK

8.fetal surveillance during labor

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