Exam 2: Uteroplacental & Fetal Physiology Pt. 2 Flashcards
Fetal circulation is ______ in contrast to adult circulation which is _____ _____.
parallel : in series
- Unlike adults, fetla circulation involves shunts and specialized vessles (essential for providing O2 and nutrients while the fetal lungs are still developing)
What are the three anatomic communication of fetal circulation?
- Ductus Venosus
- Foramen Ovale
- Ductus Arteriosus
Pulmonary vascular resistance is ____ in fetus. Why is this?
High
- Fetal lungs are collapsed & filled with fluid.
- Little pulmonary circulation.
Systemic Vascular Resistance is ____ in the fetus. Why?
Low
- Placenta has a low resistance vascular bed.
The umbilical ____ brings oxygenated blood from the placenta to the fetus.
umbilical vein.
The umbilical ____ send deoxygenated blood form the fetus back to the placenta.
umbilical arteries (2).
How does the fetus maintain adequate oxygenation when exposed to a “low” O₂ saturation?
HbF will preferentially pull O₂ from the mom’s HbA due to its higher affinity.
What are the cardiac output contributions of the right ventricle and left ventricle of the fetus?
RV = 67% of CO
LV = 33% of CO
Parallel circulation (not in-series like adults).
Which fetal vessel allows oxygenated blood from the placenta to bypass portal circulation and go straight to the inferior vena cava?
Ductus Venosus
What aspect of fetal circulation allows oxygenated blood to flow from the RA to the LA?
What does this bypass?
Foramen Ovale (FO)
- Allows bypass of immature fetal lungs.
What causes the high right-to-left shunt of the foramen ovale?
Due to pressure gradient from high fetal PVR.
What vessel diverts blood away from underdeveloped lungs?
Ductus Arteriosus
What fetal blood vessel connects the pulmonary artery and the descending aorta?
Ductus Arteriosus
What vessel carries oxygenated blood from the placenta to the fetus?
Umbilical Vein (80-85% saturated)
Where does blood from the umbilical vein go?
- 50% to fetal portal circulation
- 50% bypasses portal circulation through DV to IVC.
The percentage of umbilical vein blood directed to the liver will increase in conjunction with ______ ____.
gestational age
Does all blood from the RA bypass the lungs and go directly into the left atrium via the FO?
No. Some blood from the RA will go to the RV and then immature pulmonary circulation.
Describe the path for most of the blood through fetal circulation.
RA → FO → LA → LV → Aorta → systemic circulation.
What percentage of blood goes from the RA to the RV and subsequently perfuses the lungs?
10%
What is greater in a fetus, PVR or SVR?
PVR
fetal lungs are filled with amniotic fluid
The majority of fetal blood that went to the RV passes from the pulmonary artery through the ____ to the descending aorta to perfuse the lower body of the fetus.
DA (Ductus Arteriosus)
just another way to catch oxygenated blood to go to descending aorta
Where do the umbilical arteries originate?
Lower vena cava
What does the DV do?
Shunts blood from the liver to the heart
What does the DA do?
Shunts blood from pulmonary circulation to the ascending aorta.
What portion of the autonomic nervous system develops first and is predominant throughout fetal life?
Parasympathetic system
Because the parasympathetic nervous system is predominant in the fetus, ____ will be the initial response of the fetus
bradycardia
What are the main environmental factors affecting fetal baroreceptors and thus SNS output?
Maternal BP & stress
When does respiratory effort begin after delivery?
30 - 90 seconds typically
What respiratory changes occur at birth?
- ↓ Intrathoracic pressure = Air movement
- Lung expansion = ↑ PaO₂ ↓ PaCO₂
- ↑ pH & PAO₂ = ↓PVR
What does the decreased PVR upon birth do to pulmonary blood flow?
↑ pulmonary artery flow = RV output shifts to lungs = ↑ pulmonary blood flow
allows the blood flow to shoft to lungs (decreased pressure gradient so the blood will go to low pressure)
What does surfactant do?
↓ surface tension = prevention of alveolar collapse
When does surfactant production start?
24 - 28 weeks gestation
The ____ will constrict and close due to increased O₂ levels.
DA
Why does the foramen ovale close?
Closes due to LA pressure exceeding RA pressure
What causes LA pressure to exceed RA pressure in a neonate?
Clamping of the umbilical cord = ↑SVR = ↑LAP = ↓ right-to-left sunt
PVR decreases with the first breath
This vessel closes with the clamping of the umbilical cord due to an increase in IVC pressure.
Ductus Venosus (DV)
What four factors can cause PVR to remain elevated after delivery? (AKA Persistent Pulmonary Hypertension of Newborn)
- Hypoxia
- Acidosis
- Hypovolemia
- Hypothermia
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
What things can lead to premature constriction of the DA?
- NSAIDs
- Preterm births
- ↑ PA pressure (which decreases pulm blood flow - can lead to insufficient oxygenation and strain on heart)
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 of less important organs (blood flow redistribution)
- ↑ Adenosine accumulation = cerebral vasodilation
Why does a fetus have bradycardia in response to hypoxia?
Hypoxia = chemoreceptor stimulation = peripheral vasoconstriction = Vagal response & bradycardia
Where is more blood shunted in the event of fetal hypoxia?
DV = ↑O₂ delivery to heart & brain
What are the results of chronic fetal hypoxia?
- Fetal growth restriction
- Impaired organ function
- 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 only what?
TOCO
Contraction Frequency
How does internal uterine pressure catheter monitoring (IUPC) differ from external (TOCO) monitoring?
IUPC ccan 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
Swimmer holding their breath underwater for 30-60 seconds every 2-3 minutes.
dipping into the placental reserve during a contraction
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
What are the two problems with the uterus that result in fetal oxygenation impairment?
- Tachysystole (excessive uterine contraction)
- Tetanic Contraction
What are the two problems on the maternal side that result in fetal oxygenation impairment?
- Hypotension
- Hypoxia
Uterine contractions are quantified over a ___ minute period and averaged over ____ minutes.
10 minutes : 30 minutes
Uterine contractions are measured from the ___________ of one contraction to the beginning of the next.
beginning
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)
- 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 (mom has an infection from an amniotic sack rupture)
- Sepsis
- Acute fetal hypoxia
- Fetal heart failure
- Anemia
An Anteater Feels Chronically Sad
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)
High Fevers Buy Earaches
What are the common causes of fetal bradycardia?
- Hypoxemia (Brady is the initial response -umbilical compression or fetal head compression)
- Hypothermia
- Maternal HoTN
- Maternal hypoglycemia
- Congenital heart block
What is the fetus’s initial response to hypoxemia?
Bradycardia
What are 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!
Ex. waking someone up who is sleeping.
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.
What are the levels of FHR variability?
- Absent: range not detectable
- Minimal: detectable by ≤ 5bpm variation
- Moderate: range 6 - 25 bpm (happy place)
- Marked: range > 25bpm
There are a lot of things that can cause decreased or absent FHR variability. Whate are they? and which ones do we cause?
- Fetal sleep cycles
- General anesthesia
- More reasons for decreased/absent: prematurity, arrythmias, fetal tachy, pre-existing neurological abnormality, severe hypoxemia, beta-agrenergic antagonists, corticosteroids (betamethasone - given to help produce surfactant), ethanol
- dexamethasone, benzos, magnesium, opioids, promethazine
What are some common causes of marked FHR variability?
- Fetal stimulation
- Transient hypoxemia (ex. umbilical cord compression during labor)
- Maternal illicit drug use
What type of FHR variability is considered “good”?
What are the three types of FHR decelerations?
- Early
- Late
- Variable
Each of these can also be “prolonged” and/or “severe”
What occurs with FHR as a contraction increases in intensity?
↑ contraction = ↓ FHR
What are early decelerations?
Symmetric gradual decraese in FHR with return to baseline
- onset of decel to nadir of FHR = >/ 30 seconds
- Nadir of FHR deceleration is at peak of contraction
- FHR decreases are typically <20 bpm below baseline (benign finding)
What is the physiologic cause of benign early decelerations?
Vasovagal response to fetal head compression (↓CBF) from uterine contraction.
Early decelerations are more typical during the ____ stage of labor.
active
What type of deceleration is depicted below?
Variable decelerations
An abrupt decrease in FHR and an abrupt return to baseline with jagged edges is indicative of ____ decelerations.
variable
The onset of variable decelerations to the beginning of FHR nadir is typically ____ seconds.
< 30 seconds
What is the most common cause of variable decelerations?
Transient Hypoxemia
- Temporary cord compression (happens during most labors).
- 2ⁿᵈ stage of labor
- Oligohydramnios (low amniotic fluid)
Frequent variable decelerations or variable decelerations occurring early in labor are often an indicator for what?
Umbilical cord occlusion
Indicative for operative delivery.
What is oligohydramnios?
Low volumes of amniotic fluid
What characterizes severe decelerations?
- FHR < 70 bpm
- ↓ in FHR > 60bpm from baseline
Severe decelerations + minimal/absent FHR variability should be concerning for what?
Fetal Hypoxia
Late decelerations can be benign as long as ____ is present.
FHR variability
Causes of late decelerations
- hypoxemia (continued and can lead to lactic acidosis)
- this would be seen as a late decel + fetal tachy with minimal variability
- myocardial decompression and failure
- chorioamnionitis
- post-term gestation
- uterine hyperactivity
- maternal HoTN/hypertensive disorders/cardiac disease
- maternal smoking
- maternal anemia
- placental abruption/previa
Pathyphysiology of late decelerations
related to decrased O2 tension = sensed by chemoreceptors = vagal stimulation = decreases FHR
late decels with decrease/absent FHR varability = ominous
What type of decelerations are depicted below?
Late decelerations
What type of decelerations are depicted below?
Late decelerations
Late decelerations w/ ____ FHR variability is very bad.
absent/decreased
What type of decelerations are characterized by decrease in FHR ≥ 15bpm and lasting > 2 minutes (but less than 10 min)?
Prolonged decelerations
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
What type of decelerations are indicated below?
Prolonged decelerations
What type of deceleration is depicted below?
Severe decelerations
Early, variable, and late decelerations can also be categorized as ____ and ____.
prolonged and severe
What type of FHR tracing is exhibited below?
Sinusoidal pattern
What does persistent sinusoidal FHR tracings indicate?
Obstetric intervention
- we see smooth, wave-like undulating pattern
- cycle of 3-5 per min
- amplitude of 5-15bpm
- >20 min
What are common causes of sinusoidal pattern FHR tracings?
- Fetal anemia
- Rh disease (incompatible blood)
- Severe hypoxia
Which category of FHR tracings is predictive of normal fetal acid-base status?
Category I
What are characteristics of Category I FHR tracings?
- Baseline FHR 110 - 160 bpm
- Moderate variability
- No late/variable decels
- +/- early decels
- +/- accelerations
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
Are Category II FHR tracings predictive for abnormal fetal acid-base status?
No
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
Which category of FHR tracings is predictive for abnormal fetal acid-base status?
Category III
What are some things that can be done to address Category III FHR tracings?
- Maternal position change
- Discontinue labor augmentation (pitocin)
- Treat tachysystole
- Surgical delivery
What are the five components of the Apgar scoring system?
- HR
- Respiratory effort
- Muscle tone
- Reflex irritability
- Color
Assessed at 1min and 5min after birth and each category is given a 0, 1, or 2
Hue Runs My Chihuahua Rex
An apgar score range of ____ is considered normal.
8 - 10
An apgar score range of ____ is considered moderate impairment.
4 - 7
An apgar score range of ____ requires immediate neonate resuscitation.
0 - 3
Risk for neonate mortality is ____ proportional to the apgar 1 minute score.
inversely
Lower score = higher risk of mortality
Apgar Chart
Easy and remeadial way to remember the shit (VEAL CHOP)
