FHR: Cardiotocography Flashcards
Components of CTG
CARDIOGRAM
FHR
- Baseline FHR
- Variability
- Reactivity
TOCOGRAM
Uterine contractions
- freq, intensity)
Baseline FHR range
Normal: 110-160 bpm
Tachycardia: > 160bpm
Bradycardia: < 110bpm
- Reflects BALANCE of autonomic nervous system
- Preterm: Faster
- Postdates: Slower
Variability range
5-25bpm
Reactivity
At least 2 accelerations in 20 mins
- Transient increase in heart rate more than 15bpm and lasts 15s or more
Causes of abnormal baseline FHR (tachycardia)
- Fetal hypoxia
- Maternal pyrexia
- Fetal/maternal hyperthyroidism
- Fetal/maternal anemia
- Fetal/maternal acidosis
- Fetal tachyarrythmias
Causes of abnormal baseline FHR (bradycardia)
- 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
Variability
- 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
Reduced variability indicates
increased acidosis
increased sympathetic tone
Complete loss of variability indicates
inability of myocardium to respond
Variability range
Normal: 5-25bpm
Reduced: < 5 bpm
Saltatory: > 25 bpm (*suggests fetal maternal haemorrhage)
Variability may be affected by:
- 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
Loss of variability is a sign of
decompensation
- increased acidosis
- increased sympathetic tone
Sinusoidal waves in cardiogram
FHR with no beat-to-beat variation and no accelerations
- smooth, regular, wave-like pattern
- unstable baseline
- extremely reduced variability
Causes of sinusoidal waves
Severe fetal anemia
Fetal/maternal haemorrhage
Brain damage
Severe fetal hypoxia
Rarely: Thumb sucking
Accelerations
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
Reactive CTG means
At least 2 accelerations every 20 mins
Optimal contractions (tocogram)
3-5 contractions every 10 mins
Lasting 30-60s each
Placenta is only perfused during
uterine relaxation
Hyperstimulation vs tachysystole
Hyperstimulation
- frequent contractions and abnormal CTG
Tachysystole
- frequent contractions but normal CTG
Decelerations
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
3 main types of decelerations
Uniform decelerations
1. Early
2. Late
Variable decelerations
3. Variable
- uncomplicated vs complicated
Uniform decelerations means
1 deceleration with every contraction
- Each deceleration has similar morphology
Early deceleration vs Late deceleration
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
Variable decelerations mean
Decelerations not present with each contraction with variable recovery phase
- Each deceleration has varying morphology
- due to umbilical cord compression
*most common deceleration
Uncomplicated vs complicated variable deceleration
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)
Late decelerations often associated with
- Reduced variability
- Raised FHR baseline
- Lack of accelerations
Variable decelerations is usually due to
umbilical cord compression
Bradycardia
A prolonged deceleration as a single episode with a drop to
- FHR < 80 BPM, lasting > 2 mins
- FHR <100 BPM, lasting for > 3 mins
Cause of fetal bradycardia
- 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
Reversible causes of abnormal CTG
VE
Dorsal position
Bed pan effect
Maternal fever
Epidural
Oxytocin
Narcotics
Maternal dehydration/ hypotension
CTG changes in gradual hypoxia
HYPOXIA begins with decelerations:
1. Decelerations to protect myocardium
- Complicated variable decelerations
- Accelerations disappear
- Loss of accelerations and reduced fetal activity to conserve o2 - 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)=
- Loss of variability
- Decrease in perfusion to fetal brain - Unstable baseline or terminal bradycardia
- Severe acidosis with myocardial depression
Reassuring signs -> Compensation -> Decompensation
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
Risk factors to consider when planning delivery
Fetus with less reserves
1. IUGR
2. Preterm
- Meconium stained liquor
-> Should deliver soon, risk of meconium aspiration syndrome - Fetal anomalies
-> CTG may not be interpreted accurately - Sepsis
-> contributes to metabolic acidosis
-> less reserves
-> avoid additional hypoxic stress for fetus - Oxytocin use
-> hyperstimulation - Caesarean scar
-> Decelerations indicative of scar dehiscence
CTG predictive value
High sensitivity but low specificity
- High negative predictive value of > 90%
Signal contact of CTG can be affected by
Obesity
Polyhydramnios
Multiple gestation
Preterm
Before interpreting CTG, record for at least
20 mins first
How does umbilical cord compression cause variable decelerations?
- The umbilical vein is often occluded first causing an acceleration of the fetal heart rate in response.
- Then the umbilical artery is occluded causing a subsequent rapid deceleration.
- When pressure on the cord is reduced another acceleration occurs and then the baseline rate returns.
Reassuring CTG features
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
Non-reassuring CTG features
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
Abnormal CTG features
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
Concerning characteristics of variable decelerations
- Lasting more than 60 seconds
- Reduced baseline variability within the deceleration
- Failure to return to baseline
- Biphasic (W) shape
- No shouldering
