Uteroplacental & Fetal Physiology Pt. 2 (Exam II) Flashcards
1
Q
Fetal circulation is ______ in contrast to adult circulation which is _____ _____.
What does this mean?
A
parallel : in series
Both sides of the fetal heart provide systemic blood flow (Parallel)
2
Q
What are the three anatomic communication of fetal circulation?
A
- Ductus Venosus
- Foramen Ovale
- Ductus Arteriosus
3
Q
Pulmonary vascular resistance is ____ in fetus. Why is this?
A
High
- Fetal lungs are collapsed & filled with fluid.
- Little pulmonary circulation.
4
Q
Systemic Vascular Resistance is _____ in the fetus. Why?
A
Low
- Placenta has a low resistance vascular bed.
5
Q
The umbilical ____ brings oxygenated blood from the placenta to the fetus.
A
umbilical vein.
6
Q
The umbilical _____ send deoxygenated blood from the fetus back to the placenta.
A
umbilical arteries (2).
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%
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.
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).
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
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.
12
Q
What causes the high right-to-left shunt of the foramen ovale?
A
Due to pressure gradient from high fetal PVR.
13
Q
What vessel diverts blood away from underdeveloped lungs?
A
Ductus Arteriosus
14
Q
What fetal blood vessel connects the pulmonary artery and the descending aorta?
A
Ductus Arteriosus
15
Q
What vessel carries oxygenated blood from the placenta to the fetus?
A
Umbilical Vein (80-85% saturated)
16
Q
Where does blood from the umbilical vein go?
A
- 50% to fetal portal circulation
- 50% bypasses portal circulation through DV to IVC.
17
Q
The percentage of umbilical vein blood directed to the liver will increase in conjunction with ______ ____.
A
gestational age
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.
19
Q
Describe the path for most of the blood through fetal circulation.
A
RA → FO → LA → LV → Ascending Aorta → systemic circulation.
20
Q
What are the fetal lungs filled with?
A
Amniotic Fluid
21
Q
What percentage of blood that does not go into the FO, but rather goes into the RV will actually make it into pulmonary circulation?
A
10%
22
Q
What is greater in a fetus, PVR or SVR?
What about RAP or LAP?
A
PVR
RAP
23
Q
The majority (90%) of fetal blood from the RV passes from the pulmonary artery through the ____ to the descending aorta to perfuse the lower body of the fetus.
A
DA (Ductus Arteriosus)
24
Q
Where do the umbilical arteries originate?
A
Lower vena cava
25
What does the DV do?
Shunts blood from the liver to the heart
26
What does the DA do?
Shunts blood from pulmonary circulation to the ascending aorta.
27
What portion of the autonomic nervous system develops first and is predominant throughout fetal life?
Parasympathetic system
28
What are the main environmental factors affecting fetal baroreceptors and thus SNS output?
Maternal BP & stress
29
When does respiratory effort begin after delivery?
30 - 90 seconds typically
30
What respiratory changes occur at birth?
- ↓ Intrathoracic pressure = Air movement
- Lung expansion = ↑ PaO₂ ↓ PaCO₂
- ↑ pH & PAO₂ = **↓PVR**
31
What does the decreased PVR upon birth do to pulmonary blood flow?
↑ pulmonary artery flow = RV output shifts to lungs = ↑ pulmonary blood flow
32
What does surfactant do?
↓ surface tension = prevention of alveolar collapse
33
When does surfactant production start?
24 - 28 weeks gestation
34
The ____ will constrict and close due to increased O₂ levels.
DA
35
Why does the foramen ovale close?
Closes due to LA pressure exceeding RA pressure
36
What causes LA pressure to exceed RA pressure in a neonate?
Clamping of the umbilical cord = ↑SVR = ↑LAP = ↓ right-to-left sunt
37
This vessel closes with the clamping of the umbilical cord due to an increase in IVC pressure.
Ductus Venosus (DV)
38
What four factors can cause PVR to remain elevated after delivery?
- Hypoxia
- Acidosis
- Hypovolemia
- Hypothermia
39
What drug class when used by a mom can cause premature constriction of the ductus arteriosus and thus persistent pulmonary hypertension of the newborn?
NSAIDs
40
What things can lead to premature constriction of the DA?
- NSAIDs
- Preterm births
- ↑ PA pressure
41
What are the three main factors affecting fetal oxygenation?
- Maternal BP
- Maternal oxygenation
- Umbilical cord patency
42
How does the fetus protect itself in the instance of hypoxia?
- ↓ endothelial NO = vasoconstriction of less important organs.
- ↑ Adenosine accumulation = cerebral vasodilation
43
Why does a fetus have bradycardia in response to hypoxia?
Hypoxia = chemoreceptor stimulation = peripheral vasoconstriction = Vagal response & bradycardia
44
Where is more blood shunted in the event of fetal hypoxia?
This occurs via which vessel?
DV = ↑O₂ delivery to heart & brain
45
What are the results of prolonged fetal hypoxia?
Activation of SNS
- Catecholamine Secretion = Fetal Tachycardia
- Cardiomyocyte apoptosis (Chronic)
- Fetal demise
46
What are the two ways that fetal heart rate can be monitored?
- External: surface doppler ultrasound
- Internal: fetal scalp electrode
47
External monitoring of uterine contractions is known as ________.
This method of monitoring can determine only what?
TOCO
Contraction Frequency
48
How does internal uterine pressure catheter monitoring (IUPC) differ from external (TOCO) monitoring?
IUPC can monitor contraction **frequency** and **strength** (i.e. intrauterine pressure).
49
The fetus depends on the _______ _______ during contractions to maintain oxygenation.
What metaphor for this was using during labor?
Cardiopulmonary reserve
*Swimmer holding their breath underwater for 30-60 seconds every 2-3 minutes*.
50
What problems with the placenta present a problem with fetal oxygenation that is **unlikely to be reversible**?
- Abruption
- Infarction
- Too small of a placenta
- ↑ placental resistance
51
What are the two problems with the uterus that result in fetal oxygenation impairment?
- Tachysystole (excessive placental contraction)
- Tetanic Contraction
52
What are the two problems on the maternal side that result in fetal oxygenation impairment?
- Hypotension
- Hypoxia
53
Uterine contractions are quantified over a ___ minute period and averaged over ____ minutes.
10 minutes : 30 minutes
54
Uterine contractions are measured from the ___________ of one contraction to the beginning of the next.
beginning
55
What is considered a "normal" amount of contractions?
≤ 5 contractions in 10 minutes
56
Tachysystole is defined by > ______ contractions in a 10 minute period.
5
57
How is tachysystole treated?
- Stop Pitocin gtt (if running)
- Nitroglycerin (sublingual or IV)
- Terbutaline (β2 agonist)
58
How is a baseline FHR calculated?
Mean FHR rounded to increments of 5bpm during a 10 minute period.
59
What is the normal FHR range?
110 - 160 bpm
60
What defines FHR tachycardia?
Bradycardia?
- Tachycardia: > 160 bpm
- Bradycardia: < 110 bpm
61
What are some common causes of fetal tachycardia originating from issues on the fetal side?
- Chorioamnionitis
- Sepsis
- Acute fetal hypoxia
- Fetal heart failure
- Anemia
62
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)
63
What are the common causes of fetal bradycardia?
- Hypoxemia (umbilical compression or fetal head compression)
- Hypothermia
- Maternal HoTN
- Maternal hypoglycemia
- Congenital heart block
64
What is the fetus's initial response to hypoxemia?
Bradycardia
65
What are FHR accelerations?
Periods of increased FHR where **bpm increases by 15 and lasts at least 15 seconds**.
66
Is it a good sign if the OB is able to induce fetal heart rate accelerations?
Yes!
*Ex. waking someone up who is sleeping*.
67
What is the single most important indicator of an adequately oxygenated fetus?
FHR variability (moderate variability = good)
*Visually quantified as amplitude of peak-to-trough in bpm*.
68
What are the levels of FHR variability?
- Absent: range not detectable
- Minimal: detectable by ≤ 5bpm variation
- Moderate: range 6 - 25 bpm
- Marked: range > 25bpm
69
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
- General anesthesia
70
Minimal/absent variability causes:
- Decadron
- Benzos
- Mg Sulf
- Opioids (systemic)
- Promethazine
71
What are some common causes of marked FHR variability?
- Fetal stimulation
- Transient hypoxemia (ex. umbilical cord compression during labor)
- Maternal drug use
72
What type of FHR variability is considered "good"?
73
What are the three types of FHR decelerations?
- Early
- Late
- Variable
*Each of these can also be "prolonged" and/or "severe"*
74
What occurs with FHR as a contraction increases in intensity?
↑ contraction = ↓ FHR
## Footnote
Nadir*
75
What are early decelerations?
Decelerations associated with uterine contraction: benign
76
What is the physiologic cause of benign early decelerations?
Vasovagal response to fetal head compression (↓CBF) from uterine contraction.
77
Early decelerations are more typical during the _____ stage of labor.
active
| Baby may be larger than pelvic cavity**
78
What type of deceleration is depicted below?
Variable decelerations
79
An abrupt decrease in FHR and an abrupt return to baseline is indicative of _________ decelerations.
variable
80
The onset of variable decelerations to the beginning of FHR nadir is typically _____ seconds.
How much does the HR Decrease by?
< 30 seconds
15 bpm
81
What is the most common cause of variable decelerations?
Transient Hypoxemia
- Temporary cord compression (happens during most labors).
- 2ⁿᵈ stage of labor
- Oligohydramnios
82
Frequent variable decelerations or variable decelerations occurring early in labor are often an indicator for what?
Umbilical cord occlusion
*Indicative for operative delivery*.
83
What is oligohydramnios?
Low volumes of amniotic fluid
84
What characterizes severe decelerations?
- FHR < 70 bpm
- ↓ in FHR > 60bpm from baseline
85
Common cause of Sever decels?
Contraction lasting longer than 60 secs
- Decreased Umbilical cord flow
- Impairs Fetal CO
86
Severe decelerations + minimal/absent FHR variability should be concerning for what?
Fetal Hypoxia
87
Late decelerations *can* be benign as long as _______ is present.
FHR variability
88
What type of decelerations are depicted below?
Late decelerations
89
What type of decelerations are depicted below?
Late decelerations
90
What are some non-benign causes of late decelerations?
- Hypoxemia
- Myocardial decompensation/failure
- Chorioamnioitis
- Post-term gestation
- Uterine hyperactivity
- Maternal HoTN/HTN
- Smoking
- Anemia
- Placental abruption/previa
91
How would hypoxemia present alongside late decelerations?
Late decels + fetal tachycardia w/ minimal/absent variability
92
Late decelerations w/ _______ FHR variability is very bad.
absent/decreased
93
What type of decelerations are characterized by decrease in FHR ≥ 15bpm and lasting > 2 minutes (but less than 10 min)?
Prolonged decelerations
94
What are some of the causes of prolonged decelerations?
- Umbilical cord compression
- Prolonged maternal HoTN
- Prolonged maternal hypoxia
- Tetanic uterine contractions
- Prolonged head compression in 2ⁿᵈ stage of labor
95
What type of decelerations are indicated below?
Prolonged decelerations
96
What type of deceleration is depicted below?
Severe decelerations
97
Early, variable, and late decelerations can also be categorized as _______ and _______.
prolonged and severe
98
What type of FHR tracing is exhibited below?
Sinusoidal pattern
99
What does persistent sinusoidal FHR tracings indicate?
Obstetric intervention
100
What are common causes of sinusoidal pattern FHR tracings?
- Fetal anemia
- Rh disease (incompatible blood)
- Severe hypoxia
101
Which category of FHR tracings is predictive of normal fetal acid-base status?
Category I
102
What are characteristics of Category I FHR tracings?
- Baseline FHR 110 - 160 bpm
- Moderate variability
- No late/variable decels
- +/- early decels
- +/- accelerations
103
What are the characteristics of Category II of FHR tracings?
- Fetal tachycardia
- Absence of induced accelerations w/ fetal stimulation
- Prolonged decels > 2min but < 10min
- Recurrent late decels w/ moderate variability
104
Are Category II FHR tracings predictive for abnormal fetal acid-base status?
No
105
What are the characteristics of Category III of FHR tracings?
- Sinusoidal FHR pattern
- Absent FHR variability w/ recurrent late decels
- Recurrent variable decels
- Sustained fetal bradycardia
106
Which category of FHR tracings is predictive for abnormal fetal acid-base status?
Category III
107
What are some things that can be done to address Category III FHR tracings?
- Maternal position change
- Discontinue pitocin
- Treat tachysystole
- Surgical delivery
108
What are the five components of the Apgar scoring system?
1. HR
2. Respiratory effort
3. Muscle tone
4. Reflex irritability
5. Color
| Done at 1 min and 5 min
109
An apgar score range of _____ is considered normal.
8 - 10
110
An apgar score range of ______ is considered moderate impairment.
4 - 7
111
An apgar score range of ______ requires immediate neonate resuscitation.
0 - 3
112
Risk for neonate mortality is __________ proportional to the apgar 1 minute score.
inversely
Lower score = higher risk of mortality
