CARDIOTOCOGRAPHCTG- FOR OBSTETRIC UNIT

Physiology of fetal heart functionDefinition Components Examples

CONTENTS

The average baseline FHR in a healthy fetus at 20 weeks is 155 bpm (range 120-180 bpm)

Controlled by : - sympathetic- parasympathetic

As the parasympathetic matures with advancing gestational age, the resting heart rate ↓.

At term, the average FHR is 140 beats per minute and the normal range is 120-160 bpm.

PHYSIOLOGY OF FETAL HEART Function

Vagus nerve- sympathetic - parasympathetic

although the fetal heart is innervated by the sympathetic system as well, parasympathetic input maintains baseline heart rate.

Parasympathetic stimulation becomes dominant over sympathetic input as the fetus develops which is why the FHR is initially faster when 1st detectable and slows as the fetal matures.

Autonomic control of fetal heart rate

Vagal stimulation induces variability in the time interval between each beat secondary to influences on the vagus in the CNS : baroreceptors, chemoreceptors

CNS influences the FHR via an intergrative center in the medulla oblongata where the vagus nerve originates.

During fetal sleep, the oscillatory variation in the FHR diminishes and the variability around the baseline beat has less amplitude

commonly known as an electronic fetal monitor or external fetal monitor (EFM) or non-stress test (NST)

measures simultaneously both the fetal heart rate and the uterine contractions,

two separate disc-shaped transducers laid against the woman's abdomen.

- ultrasound transducer measures the fetal heartbeat.

- pressure-sensitive transducer (tocodynamometer (toco) - measures the strength and frequency of uterine contractions

What is CTG?

Benefits Risks

detect early fetal distress resulting from fetal hypoxia and metabolic acidosis

closer assessment of high-risk mothers

tendency to produce false-positive results

Increase LSCS statistic

4 parameters : Baseline fetal heart rate Beat to Beat Variability Accelerations Decelerations

CTG PARAMETERS

Normal CTG trace Baseline heart rate: 110-160 Baseline variability : 5-15 bpm Accelerations: 2 or more in 20 minutes.

Each of at least 15 bpm lasting at least 15s Deceleration: absent

30 seconds

5 beats

normal FHR at term 110 – 160 bpm average fetal heart rate is considered to be

the result of tonic balance between accelerator ( sympathetic ) and decelerator (parasympathetic) influences on pacemaker cells mediated via vagal slowing of heart rate

Heart rate also is under the control of arterial chemoreceptors such that both hypoxia and hypercapnia can modulate rate.

Baseline fetal heart rate

More severe and prolonged hypoxia, with a rising blood lactate level and severe metabolic acidemia, induces a prolonged fall of heart rate due to direct effects on the myocardium.

Fetal tachycardia – baseline >160 bpm over 10 minutes or more- can be nonpathologic, considered a normal rate in the premature fetus

Causes : - maternal :

- chorioamnitis- other causes of infection causing fever- use of B-sympathomimetics

- fetal - cardiac arrhythmias- fetal anemia- acute fetal blood loss- abnormal fetal conduction system

Alteration of FHR

FIGURE 4. Fetal tachycardia that is due to fetal tachyarrhythmia associated with congenital anomalies, in this case, ventricular septal defect. Fetal heart rate is 180 bpm. Notice the "spike" pattern of the fetal heart rate.

Fetal bradycardia – baseline heart rate < 110bpm for greater than 10 minutes.

Rate : 100 - 119 beats/min, in the absence of other changes, usually is not considered to represent fetal compromise.

Such low but potentially normal baseline heart rates also have been attributed to vagal response to head compression from occiput posterior or transverse positions, particularly during second-stage labor (Young and Weinstein, 1976).

Alteration n fetal heart rate

Adverse effect on fetal circulation → severe acute bradycardia- acute hypoxemia→ chemoreceptor reflex→ bradycardia- cord occlusion → fetal hypertension → baroreceptor reflex → vagal response → bradycardia

Decreased in umbilical blood flow

• Cord compression• Cord prolapse

Decrease placental exchange area

• Abruptio placenta• Uterine rupture

Impaired uterine blood flow

• Acute maternal hypotension

• Excessive uterine contraction

Decreased maternal

oxygenation

• Apnea secondary to seizures

Causes of fetal bradycardia

Defined as fluctuations in the FHR baseline of 2 cycles/min or greater with irregular amplitude and inconstant frequency.

The time interval between 2 heartbeats in a healthy fetus is seldom the same.

Normal : 5 – 15 bpm This variability is secondary to the

interaction of the sympathetic and parasympathetic reflexes

Beat to beat variability

Causes of loss of variability :- fetal sleep - administration of drugs

- narcotics, barbiturates, phenothiazines

- MgSO4- gestational age (28-30wks)- metabolic acidemia

Upward deflection in the baseline fetal heart rate of at least 15 bpm lasting for at least 15 seconds.

In pregnancies of fewer than 32 weeks of gestation, accelerations are defined as having a peak 10 beats per minute or more above the baseline and duration of 10 seconds or longer.

Accelerations

Reductions in fetal heart rate of at least 15bpm lasting for at least 15 seconds

4 types :- Type 1 (early)- physiological- Type 2 (late)- pathological - variable- prolonged

Decelerations

consists of a gradual decrease and return to baseline associated with a contraction.

Result of a physiologic chain of events that begins with head compression during a uterine contraction

the degree of deceleration is generally proportional to the contraction strength and rarely falls below 100 to 110 beats/min or 20 to 30 beats/min below baseline.

Early deceleration

early decelerations are not associated with fetal hypoxia, acidemia, or low Apgar scores

FIGURE 5. Early deceleration in a patient with an unremarkable course of labor. Notice that the onset and the return of the deceleration coincide with the start and the end of the contraction, giving the characteristic mirror image.

smooth, gradual, symmetrical decrease in fetal heart rate beginning at or after the peak of the contraction and returning to baseline only after the contraction has ended.

The magnitude of late decelerations is rarely more than 30 to 40 beats/min below baseline and typically not more than 10 to 20 beats/min.

Late decelerations usually are not accompanied by accelerations.

Late deceleration (type 2)

associated with uteroplacental insufficiency

Causes :- placental dysfunction

- placenta abruptio- maternal hypotension- uterine hyperactivity- maternal disease – DM, HPT,

Collagen-vascular disease

Inconsistent time of onset when compared to uterine contraction

The onset of deceleration commonly varies with successive contractions .

The duration is less than 2 minutes. represent fetal heart rate reflexes that

reflect either blood pressure changes due to interruption of umbilical flow or changes in oxygenation

Variable deceleration

significant variable decelerations are those decreasing to less than 70 beats/min and lasting more than 60 seconds.

Causes : - Umbilical cord entanglement- Eg:

- Umblilical around body or neck- True knot in the umbilical cord - Prolapsed umbilical cord

isolated deceleration lasting 2 minutes or longer but less than 10 minutes from onset to return to baseline.

Causes : 1) Total umbilical cord occlusion (cord

prolapse)2) Maternal hypotension3) Uterine hypertonia4) VE or artificial ruptured of membrane

Prolonged deceleration

regular, smooth, undulating form typical of a sine wave that occurs with a frequency of 2-5/minute and an amplitude range of 5-15 bpm

also characterized by a stable baseline heart rate of 120 to 160 bpm and absent beat-to-beat variability

Occurs in severe fetal anemia, as occurs in cases of Rh disease or severe hypoxia

Sinusoidal pattern

Sinusoidal Pattern

Saltatory pattern : - rapidly recurring couplets of acceleration and deceleration causing relatively large oscillations of the baseline fetal heart rate- sympathetic stimulation overrides parasympathetic dominance in response to acute but temporary hypoxemia ( umbilical cord compression )- almost exclusively seen during labour

FIGURE 2. Saltatory pattern with wide variability. The oscillations of the fetal heart rate above and below the baseline exceed 25 bpm.

Accelerations: absent for >40 minutes-first to become apparent, and any of the following

Baseline heart rate bradycardia<110 bpm Tacycardia>150 bpm

Baseline variability:<10 bpm lasting for> 40 min, greater significant if < 5 bpm

Decelerations: variable decelerations without ominous features

Suspicious CTG trace

Accelerations: absent for>40 min and any of the following

Baseline heart rate: abnormal

Baseline variability:less than 5 bpm lasting for >90 min

Deceleration Repetitive late decelerations Variable deceleration with ominous features( duration

>60s; beat loss>60 bpm;late recovery; late deceleration component;poor baseline variability btwn and/or during deceleration

Abnormal CTG tracing

Are you ready?

QUESTIONS For You…

Baseline Fetal Heart Rate? Baseline Beat to Beat Variability? Acceleration / Deceleration? Uterine activity? CTG Reactive/ Sucpicious/ Non- Reactive? Impression?

Question 1

Baseline FHR = 130 bpm Variabilitiy = 5- 15 bpm Have Acceleration No deceleration No contraction CTG reactive IMP: Normal Fetal Heart Rate

Answer 1

Question 2

BHR= 120 bpm Variability 5 to 10 bpm Prolonged deceleration Contracting 2-3 in 10 minutes,varying in

strenght Deceleration occurs after VE;variability normal

before and after deceleration

Answer 2

Question 3

1) BL=145-150 bpm2) Variability < 5bpm3) Early deceleration ( type 1 )4) Contracting 5 in 10 minutes, lasting 90 s on

average5) Head compression6) Mx

Change maternal position Reduce pitocin infusion Continue observe trace for further abnormalities

Answer 3

Question 4

1) Baseline FHR1) Twin i=140-155 bpm2) Twin ii=150-160bpm

2) Variability 1) Twin i 5-10bpm2) Twin ii 5-10bpm

3) No deceleration4) Contracting 3-4 in 10 minutes5) Normal CTG for both twins.

Answer 4

Question 5

Baseline FHR = 130 bpm Poor Beat to Beat Variability < 5 bpm Have Acceleration No Deceleration Suspicious CTG MX= Left lateral Position of the mother and

repeat CTG

Answer 5

Question 6

BHR = 160 bpm Poor beat to beat variability < 5 bpm No acceleration Prolonged deceleration until 140 bpm and

occur more than 3 min. No contraction CTG not reactive Imp: Acute fetal distress.

Answer 6

Question 7

BHR = 155 to 160 bpm Poor Beat to Beat < 5 bpm No acceleration in 20 min No Deceleration CTG not reactive Acute Fetal distress

Answer 7

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