Varney's Ch 27 Fetal Ax During Labor Flashcards
What are the five components necessary for optimal maternal–fetal gas exchange?
- Adequate flow of well-oxygenated maternal blood into the intervillous space
- A large enough placental area for gas exchange
- Efficient diffusion of gases across the placental tissues
- Unimpaired umbilical vein circulation into the fetus
- Adequate oxygen transport capacity in the fetus
What is the estimated blood flow to the uterus at the beginning of pregnancy?
20 to 50 mL per minute
What is the approximate blood flow to the uterus at term?
500 to 900 mL of maternal blood
What role does the umbilical vein play in fetal circulation?
It provides unimpaired circulation of oxygenated blood into the fetus
What is the definition of Baseline rate?
Mean FHR rounded to increments of 5 bpm during a 10-minute segment excluding periodic or episodic changes, periods of marked variability, and segments of baseline that differ by > 25 bpm. Duration must be ≥ 2 minutes.
Baseline FHR is a key measure in fetal heart monitoring.
What is the Baseline rate for Bradycardia?
Baseline rate < 110 bpm.
Bradycardia indicates a slower than normal fetal heart rate.
What is the Baseline rate for Tachycardia?
Baseline rate > 160 bpm.
Tachycardia indicates a faster than normal fetal heart rate.
Define Variability in fetal heart rate monitoring.
Fluctuations in the baseline FHR ≥ 2 cycles/min.
Variability is an important indicator of fetal well-being.
What is meant by Absent variability?
Amplitude from peak to trough undetectable.
Absent variability may indicate potential fetal distress.
What characterizes Minimal variability?
Amplitude from peak to trough > undetectable and ≤ 5 bpm.
Minimal variability can suggest some level of fetal compromise.
What is Moderate variability?
Amplitude from peak to trough 6–25 bpm.
Moderate variability is generally considered a reassuring sign.
What defines Marked variability?
Amplitude from peak to trough > 25 bpm.
Marked variability may require further evaluation.
What is an Acceleration in fetal heart rate?
Visually apparent abrupt increase (onset to peak < 30 seconds) of FHR above baseline. Peak ≥ 15 bpm. Duration ≥ 15 bpm and < 2 minutes.
Accelerations are often associated with fetal movement and are a positive sign.
Define Prolonged acceleration.
Acceleration ≥ 2 minutes and < 10 minutes.
Prolonged accelerations may indicate a response to stimuli or other factors.
What is early deceleration in fetal heart rate (FHR) monitoring?
Visually apparent gradual decrease of FHR below baseline with a return to baseline associated with a uterine contraction.
Onset of deceleration to nadir is ≥ 30 seconds, and the onset, nadir, and recovery occur simultaneously with the contraction.
How does late deceleration differ from early deceleration?
Visually apparent gradual decrease of FHR below baseline with a return to baseline associated with a uterine contraction, but the nadir occurs after the peak of the contraction.
Onset of deceleration to nadir is ≥ 30 seconds, and the onset, nadir, and recovery occur after the contraction.
Define variable deceleration in FHR monitoring.
Visually apparent abrupt decrease in FHR below baseline with a decrease ≥ 15 bpm below baseline and a duration of ≥ 15 seconds and < 2 minutes.
Onset of deceleration to nadir is < 30 seconds.
What characterizes prolonged deceleration?
Visually apparent decrease in FHR below baseline with a decrease ≥ 15 bpm below baseline and a duration of ≥ 2 minutes but < 10 minutes.
This includes the time from onset to return to baseline.
In early deceleration, when does the return to baseline occur?
Return to baseline occurs associated with a uterine contraction.
The timing aligns with the contraction’s onset, peak, and recovery.
In late deceleration, when does the nadir occur in relation to the contraction?
The nadir occurs after the peak of the contraction.
This timing is crucial for distinguishing late deceleration from early deceleration.
True or False: Variable deceleration has a gradual decrease in FHR.
False
Variable deceleration is characterized by an abrupt decrease in FHR.
Fill in the blank: In prolonged deceleration, the duration is _______ minutes but less than 10 minutes.
≥ 2
This defines the time from onset to return to baseline.
What are the three most common reasons for fetal hypoxia?
1) low oxygen in maternal blood
2) insufficient uterine/placental blood flow
3) insufficient umbilical blood flow
How can an abnormal contraction pattern cause fetal hypoxia?
Too many ctxns do not allow enough oxygen perfusion time in-between. (5 or more ctxns in 10 mins lowers FSpO2 by 20% in 30 mins)
What is a concerning cause of a transient decrease in heart rate for a fetus during labor?
fetal hypoxia
Which cranial nerve controls the fetal heart rate via parasympathetic pathway? When stimulated, does the heart rate go up or down?
10th cranial nerve (vagus nerve). When stimulated the heart rate goes down.
What is the cause of in-utero respiratory acidosis?
compromised maternal-fetal gas exchange between placenta and fetus, where the CO2 cannot be eliminated properly and builds up in the fetus.
1) What does HIE stand for? and
2) What is the newest term to use now?
1) HIE=hypoxic-ischemic encephalopathy
2) Now use “neonatal encephalopathy” (NE)
What is the term for multi-organ dysfunction of the fetus after 35 weeks?
neonatal encephalopathy (NE)
What is therapeutic hypothermia a treatment for?
neonatal encephalopathy
What is the criteria for therapeutic hypothermia?
> 36 weeks who have the following within 1 hr of birth, hx of acute perinatal event, and Apgar ≤ 5 at 10 mins or 10 mins of PPV
1) cord pH ≤ 7.0 -OR- base deficit ≥ -16
-OR-
2) cord pH 7.01-7.15 -OR- base deficit of -10 to -15
Continuous fetal monitoring showed an increase of cesarean sections by what percent when compared to intermittent fetal monitoring?
50% increase
What conditions are associated with fetal tachycardia?
1) fetal hypoxia also evidenced by late decels, recurrent variables, decreased variability
2) infection - maternal or fetal
3) fetal anemia
4) placental abruption
5) maternal hyperthyroidism
What are non-hypoxic causes of fetal bradycardia?
1) postmature fetus
2) rapid descent (head compression)
3) maternal anesthesia (epidural)
What are hypoxic causes of fetal bradycardia?
1) prolapsed cord
2) placental abruption
3) uterine rupture
4) vasa previa
At what fetal heart rate are coronary and cerebral oxygenation preserved?
80 bpm with variability
What fetal heart rate is an emergency?
60 bpm
What is the best indicator of fetal health and oxygenation?
FHR variability. This signifies that the fetus has an intact cerebral cortex, midbrain, vagus nerve, and cardiac conduction system.
Which type of deceleration “mirrors the contractions”?
Early decelerations. The onset, nadir, and resolution coincide with the contraction.
What type of decelerations are caused by decreased uteroplacental perfusion?
late decelerations
How do late decelerations align with the contractions? before, during, or after?
They start after the peak of the contraction.
What are maternal causes of chronic uteroplacental insufficiency from narrow spiral arteries, small placentas, and/or infarcts?
1) maternal HTN
2) diabetes
3) hyperthyroidism
4) autoimmune d/o
5) uterine tachysystole
What is a fetal causes of uteroplacental insufficiency?
anemia
What are common causes of variable decelerations?
1) cord compression
2) head compression during pushing
What does a sinusoidal pattern look like?
An undulating recurrent uniform FHR equally distributed 5-15 bpm above and below the baseline 2-6 cycles per min.
What Category is a FHR of 120 bpm with moderate variability and an absence of late or variable decelerations?
Category 1
What is the Category of a FHR with a HR of 120 bpm and minimal variability and no accelerations.
Category 2
What is the Category of a FHR of 165 bpm with moderate variability and accelerations?
Category 2
What is the Category of a FHR of 140 bpm with absent variability and recurrent late decelerations?
Category 3
What intervention can be used to evaluate if a fetus has a pH of 7.2 or higher?
FSS (fetal scalp stimulation) or VAS (vibroacoustic stimulation) performed between contractions.
-must elicit a FHR acceleration of 15 bpm lasting at least 15 seconds.
What interventions can be tried to improve fetal oxygenation?
1) position change (side-lying)
2) IV fluid bolus
3) O2
4) tocolytics (slow/stop ctxns)
When would you consider having the mother push with every other contraction, instead of with each contraction?
To improve fetal oxygenation and improve FHR tracings (severity or frequency of decelerations)
What is amnioinfusion used for?
Improvement in FHR when there is recurrent cord compression, recurrent variable decels or prolonged decels.
How does a bolus of IV fluids for the mother effect contractions and fetal oxygenation?
1) Can reduce the frequency of ctxns by diluting oxytocin concentrations.
2) Increase fetal O2 by optimizing placental perfusion
Is there clear evidence that maternal O2 improves the fetal oxygenation?
No
How does a preterm fetus differ on FHR tracings?
1) Higher baseline FHR
2) smaller acceleration amplitude
3) decreased variability
4) frequent short/shallow variable decels
What FHR pattern would you expect to see with infection?
Tachycardia
