Fetal Well-Being in Labor Flashcards
1
Q
Define: baseline fetal heart rate
A
- Mean FHR rounded to increments of 5 bpm during a 10-minute segment
- Excluding:
- Periodic or episodic changes
- Periods of marked variability
- Segments of baseline that differ by > 25 bpm.
- Duration must be ≥ 2 minutes.
2
Q
Define: variability
(name types)
A
- Fluctuations in the baseline FHR ≥ 2 cycles/min
- Absent variability – amplitude range undetectable
- Without decels may be idiopathic and not associated with acidemia
- Minimal variability – amplitude visually detectable but < 5 bpm
- If no decels - not associated with acidemia
- Rest cycles - typically last 20 to 40 min but sometimes as long as 75 to 80 min
- Moderate variability – amplitude range from 6 – 25 bpm
- Marked variability – amplitude > 25 bpm
- May be a response to short period of hypoxia but generally not assiciated with poor outcome
3
Q
Define: bradycardia
A
- Baseline rate < 110 bpm
- Rate < 60 bpm = emergency
- Fetus unable to increase SV to sustain adequate circulation through the heart and coronary arteries
- Both asphyxial and non-asphyxial causes possible
- Non-asphyxial causes:
- Fetal heart block
- Maternal hypothermia
- Mild bradycardia in the 100–120 bpm range can be idiopathic in the postmature fetus
- Rapid descent of presenting part or at the end of 2nd stage: when fetal head compression → increased ICP → vagal response
- Cerebral oxygenation at FHR > 80 bpm and variability retained.
- Administration of intrathecal opioids or local anesthetics for epidural analgesia.
- Maternal hypotension, s/t sympathetic block → decrease in uteroplacental blood flow.
- Transient bradycardias or prolonged decelerations usually retain normal variability, rarely associated with adverse outcomes.
- Asphyxial causes:
- Acute emergency events such as prolapsed cord, placental abruption, uterine rupture, or vasa previa
- Non-asphyxial causes:
- Bradycardia accompanied by moderate variability not associated w/ fetal acidemia (no intervention required)
4
Q
Define: tachycardia
A
- Baseline rate > 160 bpm
- Tachycardia alone not usually associated with poor outcomes in the term fetus.
- Short periods of tachycardia are a normal compensatory response to transient hypoxemia.
- Sustained tachycardia in a term fetus may be caused by developing acidemia, maternal or fetal infection, cardiac arrhythmia, or it may be idiopathic.
- Other causes include administration of beta-mimetic drugs or ephedrine given to correct maternal hypotension.
- More rarely, fetal tachycardia occurs secondary to fetal anemia (Rh isoimmunization), acute fetal blood loss (placental abruption), an abnormal fetal conduction system (fetal arrhythmia), or poorly controlled maternal hyperthyroidism.
- Sustained tachycardia, especially if accompanied by minimal variability and recurrent decelerations, may indicate that the fetus’s ability to compensate for repeated hypoxia is limited.
- May appear after recurrent decelerations present for some period of time but before a terminal bradycardia becomes evident
- Characteristic of FHR pattern evolution when acidemia is increasing
5
Q
Define: acceleration
A
- Visually apparent abrupt increase (onset to peak < 30 seconds) of FHR above baseline.
- Peak ≥ 15 bpm.
- Duration ≥ 15 bpm and < 2 minutes.
- ***GA < 32 weeks***
- Peak ≥ 10 bpm above baseline
- Duration ≥ 10 seconds is an acceleration
6
Q
Early deceleration
- Define
- Significance
- Physiological basis
- Possible causes
- Appropriate treatment
A
* Define:
* Visually apparent gradual decrease (≥ 30 seconds to nadir) of FHR below baseline.
* Return to baseline associated with a uterine contraction.
* Nadir occurs at the same time as the peak of the contraction.
* Onset/nadir/recovery of decel mirror contraction * Baroreceptor mediated * Mechanism unknown - thought to be head compression * Benign, no treatment needed
7
Q
Late deceleration
- Define
- Significance
- Physiological basis
- Possible causes
- Appropriate treatment
A
- Define:
- Visually apparent gradual decrease (≥ 30 secs to nadir) of FHR below baseline.
- Return to baseline associated with a uterine contraction.
- Nadir occurs after the peak of the contraction.
- Generally, onset/nadir/recovery of the decel occur after the onset/peak/recovery of the contraction
- Physiology:
- Contraction → decrease in uteroplacental perfusion → lower O2 levels in fetal circulation
- Hypoxemia detected by chemoreceptors in carotid artery, carotid sinus, and aortic arch.→ vagally mediated drop in FHR (alpha adrenergic response in endothelium of blood vessel → central HTN → baroreceptor → decreased FHR)
- Chemoreceptor stimulation takes time (deoxygenated blood must first traverse UV before reaching the chemoreceptors) → hence the “late” decel
- Possible causes:
- Uteroplacental insufficiency
- Significance
- Late decel + moderate variability → physiologic response to transient hypoxemia, rather than an indicator of the presence of acidemia.
- Recurrent late decels + minimal or absent variability → most commonly associated with fetal acidemia
- Appropriate treatment:
- Delivery if Cat III or concern for developing acidemia
8
Q
Variable deceleration
- Define
- Significance
- Physiological basis
- Possible causes
- Appropriate treatment
A
# * Define
* Visually apparent abrupt decrease (\< 30 secs to nadir) in FHR below baseline.
* Decrease ≥ 15 bpm below baseline. * Duration ≥ 15 seconds and \< 2 minutes from onset to return to baseline.
- Possible causes
- Cord around neck/body, true knots, frank and occult prolapse of the cord, and compression due to decreased amniotic fluid
- Physiological basis
- Baroreceptor mediated
- Cord compression
- UV compressed → decreased preload → less blood to baby → spike (shoulder) in HR
- Compression intensifies → UA compression → decreased afterload → vagal mediated HR decel
- Significance
- If return to baseline < 60 seconds with concomitant normal baseline and moderate variability - not associated with fetal acidemia.
- Recurrent variable decelerations with minimal or absent variability - associated with fetal acidemia and require urgent evaluation and consideration of intervention
- Loss of “shoulder” → often see longer variables
with slower recovery
- Appropriate treatment
9
Q
Sinusoidal pattern
- Define
- Significance
- Physiological basis
- Possible causes
- Appropriate treatment
A
- Define
- True sinusoidal extremely rare
- Absence of short-term variability
- Undulation occurs at a rate of 2 to 6 cycles per minute
- Undulating, recurrent uniform FHR equally distributed 5 to 15 bpm above/below baseline
- Significance
- Always an ominous sign → immediate intervention is indicated.
- May also appear shortly before death in a severely asphyxiated fetus
- Physiological basis
- Brainstem malfunction?
- Possible causes
- Clinically significant anemia (maternal-fetal hemorrhage following vasa previa, uterine rupture, or abruption, Rh isoimmunization)
- Appropriate treatment
- Notify the consulting physician ASAP
- Prepare patient for emergency C/S
- Notify NICU to prepare for a potentially anemic or hypovolemic newborn.
10
Q
Define: pseudosinusoidal pattern
A
- Not an NICHD-recognized FHR pattern because it is commonly the result of opioid administration, rather than being an intrinsic FHR characteristic.
- Clinically insignificant pattern
- Intermittent and bracketed by periods of moderate variability.
- Differs from a real sinusoidal pattern in 2 ways:
- Variability is retained
- > 2 to 6 cycles per minute.
11
Q
Define: cardiac arrhythmias
A
- ~ 1% to 3% of term fetus
- ~ 90% of fetal arrhythmias are transient/benign
- Consulting physician should evaluate any fetus with an arrhythmia, and a plan should be made for ongoing collaboration as long as the arrhythmia is present.
- Can be heard on audible Doppler devices and can be seen on FHR tracings, but cannot be accurately diagnosed via EFM.
- Neonatal/pediatric attendance at birth may be recommended depending on the rate and persistence of the arrhythmia.
12
Q
Define: tachysystole
A
- 5 contractions in 10 minutes averaged over a 30-minute window
- Can affect fetal gas exchange
13
Q
Contractions intensity (nose/chin/forhead and corresponding pressures
A
Contraction intensity by palpation (fingertip can usually detect IUP >20 mg Hg:
Mild – nose (< 40 mmHg via IUPC)
Moderate – chin (40 – 70 mmgHg via IUPC)
Strong – forehead (> 70 mmHg via IUPC)
14
Q
Define: uterine resting tone
A
Should be < 30 mmHg
15
Q
Category I FHR Tracing
NICHD Criteria
A
- Baseline rate: 110–160 bpm
- Baseline FHR variability: moderate
- Late or variable decelerations: absent
- Early decelerations: present or absent
- Accelerations: present or absent
16
Q
Category II FHR Tracing
NICHD Criteria
A
All FHR tracings not categorized as Category I or Category III. Includes any of these patterns:
- Baseline rate:
- Bradycardia not accompanied by absent baseline variability
- Tachycardia
- Baseline FHR variability:
- Absent (without recurrent decels)
- Minimal, or Marked
- Accelerations:
- Absence of induced accelerations after fetal stimulations
- Periodic or episodic decelerations:
- Recurrent variable decelerations accompanied by minimal or moderate baseline variability
- Prolonged deceleration > 2 minutes but < 10 minutes
- Recurrent late decelerations with moderate baseline variability
- Variable decelerations with other characteristics, such as slow return to baseline, “overshoots,” or “shoulders”
24
Q
Describe normal cord blood gases
A
Want pH > 7 and BE < - 10
25
Q
Describe abnormal cord blood gases as they correlate to respiratory and metabolic acidosis
A
Respiratory
• pH <7.25
- pO2 variable
- pCO2 >50 mmHg
- BE < -10 mEq/liter
Metabolic
• pH <7.25
- pO2 <20 mmHg
- pCO2 45-55 mmHg
- BE > -10mEq/Liter
28
Q
Umbilical and uterine blood flow
A
- Uterine spiral arteries become deinnervated during pregnancy as their endothelial linings are replaced with trophoblastic tissue → arteries become maximally → facilitate blood flow into the intervillous space
- Arteries lose their ability to constrict if pressure in the vessel drops
- Exchange of nutrients and gases occurs with the fetal blood as the maternal blood flows around the branch villi.
- Two umbilical arteries carry poorly oxygenated fetal blood to the placenta
- One umbilical vein carries oxygenated blood to the fetus.
- Placental cotyledons are separated from each other by septa projections of the decidua basalis. Each cotyledon consists of two or more main stem villi and branches.
