Uteroplacental & Fetal Physiology Pt. 4 (Exam 2) Flashcards
What are the three main factors affecting fetal oxygenation?
- Maternal BP
- Maternal oxygenation
- Umbilical cord patency
How does the fetus protect itself in the instance of hypoxia?
- ↓ endothelial NO ⇒ vasoconstriction ⇒ blood flow redistribution
- ↑ Adenosine accumulation ⇒ cerebral vasodilation
Why does a fetus have bradycardia in response to hypoxia?
- chemoreceptor stimulation ⇒ peripheral vasoconstriction
- Vagal response ⇒ bradycardia (predominant parasympathetic system)
Where is more blood shunted in the event of fetal hypoxia?
Ductus venosus & ↑O₂ delivery to heart & brain
What are the results of chronic fetal hypoxia? (weeks of months)
- Fetal growth restriction
- Impaired organ function (brain, kidney)
- Cardiomyocyte apoptosis
- Fetal demise
What are the two ways that fetal heart rate can be monitored?
- External: surface doppler ultrasound
- Internal: fetal scalp electrode
External monitoring of uterine contractions is known as ________.
This method of monitoring can determine what?
TOCO
Contraction Frequency only
How does internal uterine pressure catheter monitoring (IUPC) differ from external (TOCO) monitoring?
IUPC can monitor contraction frequency and strength (i.e. intrauterine pressure).
The fetus depends on the _______ _______ during contractions to maintain oxygenation.
What metaphor for this was using during labor?
Cardiopulmonary reserve
- Poor reserve oxygen leads to decompensation
Swimmer holding their breath underwater for 30-60 seconds every 2-3 minutes.
What problems with the placenta present a problem with fetal oxygenation that are ** not likely reversible**?
- Abruption (tear away from uterine wall)
- Infarction
- Too small of a placenta
- ↑ placental resistance
What are the two problems with the uterus that result in fetal oxygenation impairment?
- Tachysystole (excessive contraction frequency)
- Tetanic Contraction (sustained and forceful)
What are the two problems on the maternal side that result in fetal oxygenation impairment?
- Hypotension
- Hypoxia
Uterine contractions are quantified over a ______ period and averaged over ____ minutes.
10 minute period : averaged over 30 minutes
Uterine contractions are measured from ___________ of one contraction to _________ of the next.
Uterine contractions are measured from the beginning of one contraction to the beginning of the next.
What is considered a “normal” amount of contractions?
≤ 5 contractions in 10 minutes
Tachysystole is defined by > ______ contractions in a 10 minute period.
5
How is tachysystole treated?
- Stop Pitocin gtt (if running)
- Nitroglycerin (sublingual or IV) to relax uterus
- Terbutaline (β2 agonist)
How is a baseline FHR calculated?
Mean FHR rounded to increments of 5bpm during a 10 minute period.
What is the normal FHR range?
110 - 160 bpm
What defines FHR tachycardia?
Bradycardia?
- Tachycardia: > 160 bpm
- Bradycardia: < 110 bpm
What are some common causes of fetal tachycardia originating from issues on the fetal side?
- Chorioamnionitis
- Sepsis
- Acute fetal hypoxia
- Fetal heart failure
- Anemia
What are some common causes of fetal tachycardia originating from issues on the maternal side?
- Maternal hyperthyroidism
- Maternal fever
- Epi / ephedrine
- β2 agonists (Ritodrine, terbutaline)
What are the common causes of fetal bradycardia?
- Hypoxemia (umbilical compression or fetal head compression)
- Hypothermia
- Maternal HoTN
- Maternal hypoglycemia
- Congenital heart block
What is the fetus’s initial response to hypoxemia?
fetal Bradycardia
What is considered FHR accelerations?
Periods of increased FHR where bpm increases by 15 and lasts at least 15 seconds.
Is it a good sign if the OB is able to induce fetal heart rate accelerations?
Yes, it is normal and healthy
Ex. waking someone up who is sleeping.
What is the single most important indicator of an adequately oxygenated fetus?
FHR variability (moderate variability = good)
- fluctuations in baseline FHR
- irregular amplitude and frequency
- Visually quantified as amplitude of peak-to-trough in bpm
What are the levels of FHR variability?
- Absent: amplitude range not detectable
- Minimal: detectable range by ≤ 5bpm variation
- Moderate: range 6 - 25 bpm
- Marked: range > 25bpm
There are a lot of things that can cause decreased or absent FHR variability. Which one is normal and which one do we cause?
- Fetal sleep cycles
- Anesthesia (general, BZDs, opioids…)
What are some common causes of marked FHR variability?
- Fetal stimulation
- Transient hypoxemia (ex. umbilical cord compression during labor)
- Maternal drug use (illicit, stimulants…)
What type of FHR variability is considered “good”?
What response would be expected with prolonged fetal hypoxia?
Sympathetic nervous system activation ⇒ catecholamine secretion and fetal tachycardia
How are fetal monitoring strips measured?
fetal heart rate:
- y-axis BPM
TOCO:
- one box = 10 seconds
- six boxes = one minute
What is exhibited from this fetal monitor strip?
Fetal tachycardia
What is exhibited in this fetal monitor strip?
Fetal Bradycardia
What are some common drugs that are used in anesthesia that can cause minimal/absent variability in FHR?
- General anesthesia
- Benzodiazepines
- Dexamethasone
- opioids
- Promethazine
- magnesium
Review: This is what minimal/absent variability looks like on a fetal heart monitor
Review: this is what marked variability looks like on a fetal heart monitor
