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(Spring 2025) Advanced Principles A > Uteroplacental & Fetal Physiology Pt. 2 (Exam II) > Flashcards

Uteroplacental & Fetal Physiology Pt. 2 (Exam II) Flashcards

1
Q

Fetal circulation is ______ in contrast to adult circulation which is _____ _____.

A

parallel : in series

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2
Q

What are the three anatomic communication of fetal circulation?

A
  • Ductus Venosus
  • Foramen Ovale
  • Ductus Arteriosus
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3
Q

Pulmonary vascular resistance is ____ in fetus. Why is this?

A

High

  • Fetal lungs are collapsed & filled with fluid.
  • Little pulmonary circulation.
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4
Q

Systemic Vascular Resistance is _____ in the fetus. Why?

A

Low

  • Placenta has a low resistance vascular bed.
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5
Q

The umbilical ____ brings oxygenated blood from the placenta to the fetus.

A

umbilical vein.

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6
Q

The umbilical _____ send deoxygenated blood form the fetus back to the placenta.

A

umbilical arteries (2).

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7
Q

What is the PO₂ of maternal blood in the placenta?
What is the (typical) O₂ saturation of the maternal blood?

A

PO₂ = 30-35 mmHg
SaO₂ = 80-85%

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8
Q

How does the fetus maintain adequate oxygenation when exposed to a “low” O₂ saturation?

A

HbF will preferentially pull O₂ from the mom’s HbA due to its higher affinity.

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9
Q

What are the cardiac output contributions of the right ventricle and left ventricle of the fetus?

A

RV = 67% of CO
LV = 33% of CO

Parallel circulation (not in-series like adults).

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10
Q

Which fetal vessel allows oxygenated blood from the placenta to bypass portal circulation and go straight to the inferior vena cava?

A

Ductus Venosus

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11
Q

What aspect of fetal circulation allows oxygenated blood to flow from the RA to the LA?
What does this bypass?

A

Foramen Ovale (FO)

  • Allows bypass of immature fetal lungs.
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12
Q

What causes the high right-to-left shunt of the foramen ovale?

A

Due to pressure gradient from high fetal PVR.

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13
Q

What vessel diverts blood away from underdeveloped lungs?

A

Ductus Arteriosus

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14
Q

What fetal blood vessel connects the pulmonary artery and the descending aorta?

A

Ductus Arteriosus

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15
Q

What vessel carries oxygenated blood from the placenta to the fetus?

A

Umbilical Vein (80-85% saturated)

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16
Q

Where does blood from the umbilical vein go?

A
  • 50% to fetal portal circulation
  • 50% bypasses portal circulation through DV to IVC.
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17
Q

The percentage of umbilical vein blood directed to the liver will increase in conjunction with ______ ____.

A

gestational age

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18
Q

Does all blood from the RA bypass the lungs and go directly into the left atrium via the FO?

A

No. Some blood from the RA will go to the RV and then immature pulmonary circulation.

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19
Q

Describe the path for most of the blood through fetal circulation.

A

RA → FO → LA → LV → Aorta → systemic circulation.

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20
Q

What percentage of blood goes from the RA to the RV and subsequently perfuses the lungs?

A

10%

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21
Q

What is greater in a fetus, PVR or SVR?

A

PVR

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22
Q

The majority of fetal blood passes from the pulmonary artery through the ____ to the descending aorta to perfuse the lower body of the fetus.

A

DA (Ductus Arteriosus)

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23
Q

Where do the umbilical arteries originate?

A

Lower vena cava

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24
Q

What does the DV do?

A

Shunts blood from the liver to the heart

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25
Q

What does the DA do?

A

Shunts blood from pulmonary circulation to the ascending aorta.

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26
Q

What portion of the autonomic nervous system develops first and is predominant throughout fetal life?

A

Parasympathetic system

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27
Q

What are the main environmental factors affecting fetal baroreceptors and thus SNS output?

A

Maternal BP & stress

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28
Q

When does respiratory effort begin after delivery?

A

30 - 90 seconds typically

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29
Q

What respiratory changes occur at birth?

A
  • ↓ Intrathoracic pressure = Air movement
  • Lung expansion = ↑ PaO₂ ↓ PaCO₂
  • ↑ pH & PAO₂ = ↓PVR
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30
Q

What does the decreased PVR upon birth do to pulmonary blood flow?

A

↑ pulmonary artery flow = RV output shifts to lungs = ↑ pulmonary blood flow

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31
Q

What does surfactant do?

A

↓ surface tension = prevention of alveolar collapse

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32
Q

When does surfactant production start?

A

24 - 28 weeks gestation

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33
Q

The ____ will constrict and close due to increased O₂ levels.

A

DA

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34
Q

Why does the foramen ovale close?

A

Closes due to LA pressure exceeding RA pressure

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35
Q

What causes LA pressure to exceed RA pressure in a neonate?

A

Clamping of the umbilical cord = ↑SVR = ↑LAP = ↓ right-to-left sunt

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36
Q

This vessel closes with the clamping of the umbilical cord due to an increase in IVC pressure.

A

Ductus Venosus (DV)

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37
Q

What four factors can cause PVR to remain elevated after delivery?

A
  • Hypoxia
  • Acidosis
  • Hypovolemia
  • Hypothermia
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38
Q

What drug class when used by a mom can cause premature constriction of the ductus arteriosus and thus persistent pulmonary hypertension of the newborn?

A

NSAIDs

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39
Q

What things can lead to premature constriction of the DA?

A
  • NSAIDs
  • Preterm births
  • ↑ PA pressure
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40
Q

What are the three main factors affecting fetal oxygenation?

A
  • Maternal BP
  • Maternal oxygenation
  • Umbilical cord patency
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41
Q

How does the fetus protect itself in the instance of hypoxia?

A
  • ↓ endothelial NO = vasoconstriction of less important organs.
  • ↑ Adenosine accumulation = cerebral vasodilation
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42
Q

Why does a fetus have bradycardia in response to hypoxia?

A

Hypoxia = chemoreceptor stimulation = peripheral vasoconstriction = Vagal response & bradycardia

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43
Q

Where is more blood shunted in the event of fetal hypoxia?

A

DV = ↑O₂ delivery to heart & brain

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44
Q

What are the results of chronic fetal hypoxia?

A
  • Fetal growth restriction
  • Impaired organ function
  • Cardiomyocyte apoptosis
  • Fetal demise
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45
Q

What are the two ways that fetal heart rate can be monitored?

A
  • External: surface doppler ultrasound
  • Internal: fetal scalp electrode
46
Q

External monitoring of uterine contractions is known as ________.

This method of monitoring can determine only what?

A

TOCO

Contraction Frequency

47
Q

How does internal uterine pressure catheter monitoring (IUPC) differ from external (TOCO) monitoring?

A

IUPC ccan monitor contraction frequency and strength (i.e. intrauterine pressure).

48
Q

The fetus depends on the _______ _______ during contractions to maintain oxygenation.

What metaphor for this was using during labor?

A

Cardiopulmonary reserve

Swimmer holding their breath underwater for 30-60 seconds every 2-3 minutes.

49
Q

What problems with the placenta present a problem with fetal oxygenation that is unlikely to be reversible?

A
  • Abruption
  • Infarction
  • Too small of a placental
  • ↑ placental resistance
50
Q

What are the two problems with the uterus that result in fetal oxygenation impairment?

A
  • Tachysystole (excessive placental contraction)
  • Tetanic Contraction
51
Q

What are the two problems on the maternal side that result in fetal oxygenation impairment?

A
  • Hypotension
  • Hypoxia
52
Q

Uterine contractions are quantified over a ___ minute period and averaged over ____ minutes.

A

10 minutes : 30 minutes

53
Q

Uterine contractions are measured from the ___________ of one contraction to the beginning of the next.

54
Q

What is considered a “normal” amount of contractions?

A

≤ 5 contractions in 10 minutes

55
Q

Tachysystole is defined by > ______ contractions in a 10 minute period.

56
Q

How is tachysystole treated?

A
  • Stop Pitocin gtt (if running)
  • Nitroglycerin (sublingual or IV)
  • Terbutaline (β2 agonist)
57
Q

How is a baseline FHR calculated?

A

Mean FHR rounded to increments of 5bpm during a 10 minute period.

58
Q

What is the normal FHR range?

A

110 - 160 bpm

59
Q

What defines FHR tachycardia?
Bradycardia?

A
  • Tachycardia: > 160 bpm
  • Bradycardia: < 110 bpm
60
Q

What are some common causes of fetal tachycardia originating from issues on the fetal side?

A
  • Chorioamnionitis
  • Sepsis
  • Acute fetal hypoxia
  • Fetal heart failure
  • Anemia
61
Q

What are some common causes of fetal tachycardia originating from issues on the maternal side?

A
  • Maternal hyperthyroidism
  • Maternal fever
  • Epi / ephedrine
  • β2 agonists (Ritodrine, terbutaline)
62
Q

What are the common causes of fetal bradycardia?

A
  • Hypoxemia (umbilical compression or fetal head compression)
  • Hypothermia
  • Maternal HoTN
  • Maternal hypoglycemia
  • Congenital heart block
63
Q

What is the fetus’s initial response to hypoxemia?

A

Bradycardia

64
Q

What are FHR accelerations?

A

Periods of increased FHR where bpm increases by 15 and lasts at least 15 seconds.

65
Q

Is it a good sign if the OB is able to induce fetal heart rate accelerations?

A

Yes!

Ex. waking someone up who is sleeping.

66
Q

What is the single most important indicator of an adequately oxygenated fetus?

A

FHR variability (moderate variability = good)

Visually quantified as amplitude of peak-to-trough in bpm.

67
Q

What are the levels of FHR variability?

A
  • Absent: range not detectable
  • Minimal: detectable by ≤ 5bpm variation
  • Moderate: range 6 - 25 bpm
  • Marked: range > 25bpm
68
Q

There are a lot of things that can cause decreased or absent FHR variability. Which one is normal and which one do we cause?

A
  • Fetal sleep cycles
  • General anesthesia
69
Q

What are some common causes of marked FHR variability?

A
  • Fetal stimulation
  • Transient hypoxemia (ex. umbilical cord compression during labor)
  • Maternal drug use
70
Q

What type of FHR variability is considered “good”?

71
Q

What are the three types of FHR decelerations?

A
  • Early
  • Late
  • Variable

Each of these can also be “prolonged” and/or “severe”

72
Q

What occurs with FHR as a contraction increases in intensity?

A

↑ contraction = ↓ FHR

73
Q

What are early decelerations?

A

Decelerations associated with uterine contraction: benign

74
Q

What is the physiologic cause of benign early decelerations?

A

Vasovagal response to fetal head compression (↓CBF) from uterine contraction.

75
Q

Early decelerations are more typical during the _____ stage of labor.

76
Q

What type of deceleration is depicted below?

A

Variable decelerations

77
Q

An abrupt decrease in FHR and an abrupt return to baseline is indicative of _________ decelerations.

78
Q

The onset of variable decelerations to the beginning of FHR nadir is typically _____ seconds.

A

< 30 seconds

79
Q

What is the most common cause of variable decelerations?

A

Transient Hypoxemia

  • Temporary cord compression (happens during most labors).
  • 2ⁿᵈ stage of labor
  • Oligohydramnios
80
Q

Frequent variable decelerations or variable decelerations occurring early in labor are often an indicator for what?

A

Umbilical cord occlusion

Indicative for operative delivery.

81
Q

What is oligohydramnios?

A

Low volumes of amniotic fluid

82
Q

What characterizes severe decelerations?

A
  • FHR < 70 bpm
  • ↓ in FHR > 60bpm from baseline
83
Q

Severe decelerations + minimal/absent FHR variability should be concerning for what?

A

Fetal Hypoxia

84
Q

Late decelerations can be benign as long as _______ is present.

A

FHR variability

85
Q

What type of decelerations are depicted below?

A

Late decelerations

86
Q

What type of decelerations are depicted below?

A

Late decelerations

87
Q

What are some non-benign causes of late decelerations?

A
  • Hypoxemia
  • Myocardial decompensation/failure
  • Chorioamnioitis
  • Post-term gestation
  • Uterine hyperactivity
  • Maternal HoTN/HTN
  • Smoking
  • Anemia
  • Placental abruption/previa
88
Q

How would hypoxemia present alongside late decelerations?

A

Late decels + fetal tachycardia w/ minimal/absent variability

89
Q

Late decelerations w/ _______ FHR variability is very bad.

A

absent/decreased

90
Q

What type of decelerations are characterized by decrease in FHR ≥ 15bpm and lasting > 2 minutes (but less than 10 min)?

A

Prolonged decelerations

91
Q

What are some of the causes of prolonged decelerations?

A
  • Umbilical cord compression
  • Prolonged maternal HoTN
  • Prolonged maternal hypoxia
  • Tetanic uterine contractions
  • Prolonged head compression in 2ⁿᵈ stage of labor
92
Q

What type of decelerations are indicated below?

A

Prolonged decelerations

93
Q

What type of deceleration is depicted below?

A

Severe decelerations

94
Q

Early, variable, and late decelerations can also be categorized as _______ and _______.

A

prolonged and severe

95
Q

What type of FHR tracing is exhibited below?

A

Sinusoidal pattern

96
Q

What does persistent sinusoidal FHR tracings indicate?

A

Obstetric intervention

97
Q

What are common causes of sinusoidal pattern FHR tracings?

A
  • Fetal anemia
  • Rh disease (incompatible blood)
  • Severe hypoxia
98
Q

Which category of FHR tracings is predictive of normal fetal acid-base status?

A

Category I

99
Q

What are characteristics of Category I FHR tracings?

A
  • Baseline FHR 110 - 160 bpm
  • Moderate variability
  • No late/variable decels
  • +/- early decels
  • +/- accelerations
100
Q

What are the characteristics of Category II of FHR tracings?

A
  • Fetal tachycardia
  • Absence of induced accelerations w/ fetal stimulation
  • Prolonged decels > 2min but < 10min
  • Recurrent late decels w/ moderate variability
101
Q

Are Category II FHR tracings predictive for abnormal fetal acid-base status?

102
Q

What are the characteristics of Category III of FHR tracings?

A
  • Sinusoidal FHR pattern
  • Absent FHR variability w/ recurrent late decels
  • Recurrent variable decels
  • Sustained fetal bradycardia
103
Q

Which category of FHR tracings is predictive for abnormal fetal acid-base status?

A

Category III

104
Q

What are some things that can be done to address Category III FHR tracings?

A
  • Maternal position change
  • Discontinue pitocin
  • Treat tachysystole
  • Surgical delivery
105
Q

What are the five components of the Apgar scoring system?

A
  1. HR
  2. Respiratory effort
  3. Muscle tone
  4. Reflex irritability
  5. Color
106
Q

An apgar score range of _____ is considered normal.

107
Q

An apgar score range of ______ is considered moderate impairment.

108
Q

An apgar score range of ______ requires immediate neonate resuscitation.

109
Q

Risk for neonate mortality is __________ proportional to the apgar 1 minute score.

A

inversely

Lower score = higher risk of mortality

(Spring 2025) Advanced Principles A (11 decks)

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