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m4 obgyn > FHR: Cardiotocography > Flashcards

FHR: Cardiotocography Flashcards

1
Q

Components of CTG

A

CARDIOGRAM
FHR
- Baseline FHR
- Variability
- Reactivity

TOCOGRAM
Uterine contractions
- freq, intensity)

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2
Q

Baseline FHR range

A

Normal: 110-160 bpm
Tachycardia: > 160bpm
Bradycardia: < 110bpm

  • Reflects BALANCE of autonomic nervous system
  • Preterm: Faster
  • Postdates: Slower
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3
Q

Variability range

A

5-25bpm

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4
Q

Reactivity

A

At least 2 accelerations in 20 mins
- Transient increase in heart rate more than 15bpm and lasts 15s or more

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5
Q

Causes of abnormal baseline FHR (tachycardia)

A
  • Fetal hypoxia
  • Maternal pyrexia
  • Fetal/maternal hyperthyroidism
  • Fetal/maternal anemia
  • Fetal/maternal acidosis
  • Fetal tachyarrythmias
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6
Q

Causes of abnormal baseline FHR (bradycardia)

A
  • Severe fetal hypoxia
  • Maternal beta-blocker therapy
  • Hypothyroidism
  • Fetal heart block
  • Hypotension
  • Epidural
  • Change in maternal position, vagal reflex due to VE
  • One of the 3 major emergencies
    1. Cord prolapse
    2. Placental abruption
    3. Scar rupture
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7
Q

Variability

A
  • Beat to beat variations in FHR that are NOT accelerations or decelerations
  • Difference between highest and lowest point of the trace in any 1 minute segment
  • Indicates ability of CNS to monitor and adjust CVS
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8
Q

Reduced variability indicates

A

increased acidosis
increased sympathetic tone

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9
Q

Complete loss of variability indicates

A

inability of myocardium to respond

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10
Q

Variability range

A

Normal: 5-25bpm
Reduced: < 5 bpm
Saltatory: > 25 bpm (*suggests fetal maternal haemorrhage)

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11
Q

Variability may be affected by:

A
  • Fetus’ sleep-wake cycle (~15mins, should not exceed 40mins)
  • Drugs e.g. MgSO4, methyldopa, opioids, steroids
  • GA < 28w (immature autonomic nervous system)
  • Maternal or fetal acidosis
  • Fetal stroke
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12
Q

Loss of variability is a sign of

A

decompensation
- increased acidosis
- increased sympathetic tone

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13
Q

Sinusoidal waves in cardiogram

A

FHR with no beat-to-beat variation and no accelerations
- smooth, regular, wave-like pattern
- unstable baseline
- extremely reduced variability

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14
Q

Causes of sinusoidal waves

A

Severe fetal anemia
Fetal/maternal haemorrhage
Brain damage
Severe fetal hypoxia
Rarely: Thumb sucking

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15
Q

Accelerations

A

Intermittent increase in FHR of > 15 beats lasting for 15 seconds
- Signifies normal fetal oxygenation and verify that fetus has capacity to respond
- Mainly due to somatic nervous system eg. kicks, movements

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16
Q

Reactive CTG means

A

At least 2 accelerations every 20 mins

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17
Q

Optimal contractions (tocogram)

A

3-5 contractions every 10 mins
Lasting 30-60s each

18
Q

Placenta is only perfused during

A

uterine relaxation

19
Q

Hyperstimulation vs tachysystole

A

Hyperstimulation
- frequent contractions and abnormal CTG

Tachysystole
- frequent contractions but normal CTG

20
Q

Decelerations

A

Intermittent drop in FHR of > 15 beats lasting for 15 seconds
- Signifies physiologic compensation to decrease heart rate to protect the heart in hypoxia by preserving myocardial oxygenation and perfusion

21
Q

3 main types of decelerations

A

Uniform decelerations
1. Early
2. Late

Variable decelerations
3. Variable
- uncomplicated vs complicated

22
Q

Uniform decelerations means

A

1 deceleration with every contraction
- Each deceleration has similar morphology

23
Q

Early deceleration vs Late deceleration

A

Early deceleration
- Lowest dip coincides WITH contraction peak
- due to fetus head compression -> increase fetal intracranial pressure causing increased vagal tone
- physiological

Late deceleration
- Lowest dip coincides AFTER contraction peak
- due to insufficient blood flow to uterus and placenta -> decrease blood flow to fetus -> fetal hypoxia and acidosis
- causes include: maternal hypotension, pre-eclampsia, uterine hyperstimulation

24
Q

Variable decelerations mean

A

Decelerations not present with each contraction with variable recovery phase
- Each deceleration has varying morphology
- due to umbilical cord compression

*most common deceleration

25
Q

Uncomplicated vs complicated variable deceleration

A

Uncomplicated variable decelerations
- Drop by <60 bpm for
<60s
- Presence of shouldering (accelerations before and after a deceleration) which indicates that fetus can mount a tachycardic response to compensate (fetus not yet hypoxic and is compensating for the reduced blood flow)

Complicated variable decelerations
- Drop by ≥60 bpm for ≥60s
- Absence of shouldering (suggests fetus is become hypoxic)

26
Q

Late decelerations often associated with

A
  • Reduced variability
  • Raised FHR baseline
  • Lack of accelerations
27
Q

Variable decelerations is usually due to

A

umbilical cord compression

28
Q

Bradycardia

A

A prolonged deceleration as a single episode with a drop to
- FHR < 80 BPM, lasting > 2 mins
- FHR <100 BPM, lasting for > 3 mins

29
Q

Cause of fetal bradycardia

A
  • Severe fetal hypoxia
  • Maternal beta-blocker therapy
  • Hypothyroidism
  • Fetal heart block
  • Hypotension
  • Epidural
  • Change in maternal position, vagal reflex due to VE
  • One of the 3 major emergencies
    1. Cord prolapse
    2. Placental abruption
    3. Scar rupture
30
Q

Reversible causes of abnormal CTG

A

VE
Dorsal position
Bed pan effect
Maternal fever
Epidural
Oxytocin
Narcotics
Maternal dehydration/ hypotension

31
Q

CTG changes in gradual hypoxia

A

HYPOXIA begins with decelerations:
1. Decelerations to protect myocardium
- Complicated variable decelerations

  1. Accelerations disappear
    - Loss of accelerations and reduced fetal activity to conserve o2
  2. Baseline FHR increases
    - due to secretion of catecholamines

=remains in compensated stress (stable baseline FHR and normal variability)=

=tips into decompensation state (unstable baseline and changes in variability)=

  1. Loss of variability
    - Decrease in perfusion to fetal brain
  2. Unstable baseline or terminal bradycardia
    - Severe acidosis with myocardial depression
32
Q

Reassuring signs -> Compensation -> Decompensation

A

Good variability -> Preserved variability -> Loss of variability

Normal baseline -> Rising baseline -> Rising or unstable baseline

Presence of accelerations -> Absence of accelerations -> Absence of accelerations

Absence of deep, prolonged decelerations -> Widening or deepening decelerations -> Wider and deeper decelerations

33
Q

Risk factors to consider when planning delivery

A

Fetus with less reserves
1. IUGR
2. Preterm

  1. Meconium stained liquor
    -> Should deliver soon, risk of meconium aspiration syndrome
  2. Fetal anomalies
    -> CTG may not be interpreted accurately
  3. Sepsis
    -> contributes to metabolic acidosis
    -> less reserves
    -> avoid additional hypoxic stress for fetus
  4. Oxytocin use
    -> hyperstimulation
  5. Caesarean scar
    -> Decelerations indicative of scar dehiscence
34
Q

CTG predictive value

A

High sensitivity but low specificity
- High negative predictive value of > 90%

35
Q

Signal contact of CTG can be affected by

A

Obesity
Polyhydramnios
Multiple gestation
Preterm

36
Q

Before interpreting CTG, record for at least

A

20 mins first

37
Q

How does umbilical cord compression cause variable decelerations?

A
  1. The umbilical vein is often occluded first causing an acceleration of the fetal heart rate in response.
  2. Then the umbilical artery is occluded causing a subsequent rapid deceleration.
  3. When pressure on the cord is reduced another acceleration occurs and then the baseline rate returns.
38
Q

Reassuring CTG features

A

Baseline FHR: 110-160 bpm
Baseline variability: 5-25 bpm
Presence of accelerations
- Absence in a normal CTG is not significant
Decelerations:
- None or early

39
Q

Non-reassuring CTG features

A

Baseline FHR: either
- 100-109 bpm
- 161-180 bpm

Baseline variability: either
- < 5 for 30-50 mins
- > 25 for 15-25 mins

Absence of accelerations

Decelerations: either
- Variable decelerations with no concerning characteristics for 90 minutes or more
- Variable decelerations with any concerning characteristics in up to 50% of contractions for 30 minutes or more
- Variable decelerations with any concerning characteristics in over 50% of contractions for less than 30 minutes
- Late decelerations in over 50% of contractions for less than 30 minutes, with no maternal or fetal clinical risk factors such as vaginal bleeding or significant meconium

40
Q

Abnormal CTG features

A

Baseline FHR: either
- < 100 bpm
- > 180 bpm

Baseline variability: either
- < 5 for more than 50 minutes
- > 25 for more than 25 minutes
- Sinusoidal

Absence of accelerations

Decelerations: either
- Variable decelerations with any concerning characteristics in over 50% of contractions for 30 minutes (or less if any maternal or fetal clinical risk factors present)
- Late decelerations for 30 minutes (or less if any maternal or fetal clinical risk factors present)
- Acute bradycardia, or a single prolonged deceleration lasting 3 minutes or more

41
Q

Concerning characteristics of variable decelerations

A
  • Lasting more than 60 seconds
  • Reduced baseline variability within the deceleration
  • Failure to return to baseline
  • Biphasic (W) shape
  • No shouldering

m4 obgyn (37 decks)

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