Test 2: Uteroplacental & Fetal Physiology Part 2 Flashcards
What does MVU stand for?
Montevideo Units
MVU is the sum of intrauterine pressure measured over a 10-min period
What does TOCO stand for?
Tocodynamometer
What does IUPC stand for?
Intrauterine Pressure Catheter
What does FSE stand for?
Fetal Scalp Electrode
What does CPD stand for?
Cephalopelvic Disproportion
What does BPP stand for?
Biophysical Profile
What does DA stand for?
Ductus Arteriosus
What does FO stand for?
Foramen Ovale
What does DV stand for?
Ductus Venous
What does FHR stand for?
Fetal Heart Rate
What are the key differences between fetal circulation and adult circulation?
- The placenta functions as the organ of gas exchange for the fetus.
- Fetal circulation is parallel, and adult circulation is in series.
- There are 3 anatomic communications in fetal circulation (Ductus Venousus, Foramen Oval, Ductus Arteriosus
- Pulmonary Vascular Resistance is HIGH in the fetus
- SVR is LOW in the fetus
- HbF has a higher affinity for O2 than Adult HbA
What structure brings oxygenated blood from the placenta to the fetus?
Umbilical Vein
What structure brings oxygen-poor blood from the fetus back to the placenta?
Umbilical Arteries
What is the PO2 and O2 Saturation of the Maternal Blood in the placenta?
- PO2: 30 to 35 mmHg
- O2 saturation: 80-85%
How does the fetus maintain adequate oxygenation exposed to a “low” O2 saturation?
- Maternal Hemoglobin in the intervillous space is ready to release oxgyen
- Fetal Hemoglobin in the intervillous space is ready to receive oxygen.
When maternal blood enters the fetus, the oxygen saturation increases to _______ % (range)
- 90-95%
What does it mean that the fetal circulation is in parallel?
Systemic blood flow is provided by both the right and left heart.
What does it mean that the adult fetal circulation is in series?
- The right side of the heart provides pulmonary blood flow
- The left side of the heart provides systemic blood flow
In fetal circulation, the right ventricle contributes ____% of CO.
67%
In fetal circulation, the left ventricle contributes ____% of CO.
33%
What is the Ductus Venosus?
Blood vessel that allows oxygenated blood from the placenta to bypass immature portal (liver) circulation and go straight to the inferior vena cava.
What is the Foramen Ovale?
Opening that directs oxygenated blood from RA → LA (bypassing immature fetal lungs).
Right to Left shunt is d/t a pressure gradient created by high fetal PVR.
What is the Ductus Arteriosus?
Blood vessel that connects Pulmonary Artery to Descending Aorta, diverting blood away from underdeveloped lungs.
The ______ carries oxygenated blood (SpO2 80-85%) and nutrients from the placenta to the fetus.
Umbilical Vein
About half of the blood coming in through the umbilical vein goes to the ____________.
Fetal Portal Circulation
About half of the blood coming in through the umbilical vein bypasses the fetal portal circulation through the ______ and on to the IVC.
Ductus Venosus
Percentage of the blood directed to the liver increases with gestational age
What happens to oxygenated blood once it is in the fetal IVC?
- The oxygenated blood mixes with a small amount of deoxygenated blood returning from the fetus’s lower body.
- The mixed blood then enters the RA
In fetal circulation, the majority of the blood in the RA will pass through the ______ directly into the LA.
Foramen Ovale
Some blood form the RA will go to RV and then through immature pulmonary circulation
What are the three benefits of having a Foramen Ovale?
- Bypassing the immature lungs
- Conserving energy
- Optimizing oxygen delivery to fetal heart and brain
In fetal circulation, blood in the LA will then pass through the LV and exit to the Ascending Aorta to supply what structures?
- Coronary Circulation
- Cerebral Circulation
- Upper Body of the Fetus
Fetal Circulation Pathway
RA → ____ → ____ → ____ → ____ → Systemic Circulation
RA → FO → LA → LV → AA → Systemic Circulation
What are fetal lungs filled with?
Amniotic Fluids
What causes the Right to Left shunt through the Foramen Ovale?
- High Fetal PVR
- RA pressure > LA Pressure
In fetal circulation, ______% of the blood goes from RV → PA goes through the pulmonary circulation.
Of this amount, the majority (90%) of this blood passes through the ______ to the descending aorta to perfuse the lower body of the fetus.
- 10%
- Ductus Arteriosus
This is because PVR > SVR
What structure will receive deoxygenated blood from the fetus → placenta?
Umbilical Arteries
The umbilical arteries will feed the placental villi for gas, nutrient, and waste exchange.
Fetal Circulation
How is the Fetal Circulation regulated?
- Sensory Input to the Autonomic Nervous System
- Baroreceptors in the aortic arch and carotid arteries sense BP changes r/t environmental factors (Maternal BP, stress)
- Sends info to ANS
- Adjustments made in FHR and blood vessel tone → Maintenance of perfusion
What ANS is developed first and is predominant throughout fetal life?
Parasympathetic Nervous System
What organ systems will most profoundly change during the transition from a fetus to a neonate?
- Pulmonary System
- Cardiovascular System
Happens in a matter of minutes following birth
How long does it take for respiratory efforts to begin after delivery?
30-90 seconds after delivery
Describe the pathophysiology of how Pulmonary Vascular Resistance is decreased after a baby is born.
- When the baby takes its first breath, intrathoracic pressure decreases → air enters the lungs
- Lung expansion: ↑ PaO2 and ↓ PaCO2
- ↑ pH and ↑ Alveolar O2 Tension
- ↓ PVR
What happens to RV output when there is an increase in pulmonary artery flow?
- RV output will shift to the lungs.
- Increase blood flow through the lungs.
When does the fetus produce surfactant?
24-28 weeks of gestation
What does surfactant do?
Reduces surface tension and prevent alveolar collapse
The Ductus Arteriosus will constrict and close after birth d/t ____________.
Increase O2 levels
The Foramen Ovale closes shortly after birth as ____________ pressure exceeds ___________ pressure.
Left Atrial Pressure exceeds Right Atrial Pressure.
How does clamping of the umbilical cord decrease Right to Left Shunt?
- Clamping of the umbilical cord
- Increase SVR
- Increase LA Pressure
- Decrease Right → Left Shunt
PVR also decreases with first breath which will also decrease Right to Left Shunt
Ductus Venosus closes with clamping of the umbilical cord which will increase _________ pressure.
IVC
Pulmonary Vascular Resistance can remain elevated after delivery d/t these four factors.
- Hypoxia
- Acidosis
- Hypovolemia
- Hypothermia
What can cause premature constriction of the Ductus Arteriosus, leading to Persistent Pulmonary Hypertension in a Newborn?
- Maternal NSAID use
- Preterm births
These factors can lead to increase PA pressure and decreased pulmonary blood flow, insufficent oxygenation, and strain on the heart.
With persistent pulmonary hypertension in a newborn, what are the effects of right-to-left shunting?
- Increase acidosis
- Hypoxia
Fetal oxygenation is dependent on what three factors?
- Maternal BP
- Maternal Oxygenation
- Patency of Umbilical Cord
What can cause fetal hypoxemia?
Problem with O2 transfer in placenta, uterus, or mother’s perfusion to the uterus
Describe the protective mechanism of the fetus when O2 demand exceeds supply.
- Decrease endothelial release of Nitric Oxide
- Leading to vasoconstriction
- Leading to blood flow redistribution to the brain and heart
- There will be adenosine accumulation, which will cause vasodilation of cerebral vessels
How do the fetus and placenta alter metabolism with fetal hypoxia?
- Stimulation of the chemoreceptors → intense peripheral vasoconstriction
- Leading to vagal response → bradycardia
- Increases amount of blood shunted through Ductus Venosus
- Increase O2 delivery to heart and brain
What is the initial fetal response to fetal hypoxia (during labor, delivery contractions, cord compression)?
- Bradycardia d/t increased vagal activity
Predominant parasympathetic system.
Brain and heart sparing for the fetus.
What is considered prolonged fetal hypoxia?
Anything longer than a few minutes.
Describe the physiological effects of the fetus with prolonged hypoxia.
- Activation of the sympathetic nervous system
- Increase catecholamine secretions
- Fetal Tachycardia
Longer periods of hypoxia will lead to fetal demise
What are the effects of chronic hypoxia (occurs over weeks or months)?
- Fetal growth restrictions
- Impaired brain and kidney functions
- Apoptosis of cardiomyocytes
- Fetal demise
Electronic fetal monitoring is a combination of what two factors?
What is the purpose of fetal monitoring?
- FHR interpretation and Contractions
- Evaluate fetal well-being, detect early distress, and
allow intervention before permanent injury
What is used to monitor FHR externally?
How about internally?
- Surface Doppler ultrasound (external)
- Fetal scalp electrode (internal)
What is used to monitor contractions externally?
How about internally?
- Tocodynamometer (external)
- Intrauterine pressure catheter (IUPC)
What is the biggest difference between TOCO and IUPC?
- TOCO is an external monitor that measures contraction frequency ONLY
- IUPC is an internal monitor that measures contraction frequency AND contraction strength
How does a fetus tolerate contractions?
- Similar to how we hold our breaths underwater, we rely on our cardiopulmonary reserves.
- The fetus has placental reserves when the uterus contracts and relaxes
Contractions = swimmer underwater for ________ seconds (range) every 2-3 minutes.
30-60 seconds
How long can a healthy fetus tolerate contractions/submersions?
Hours
What can poor reserve oxygen “intake” and impaired oxygen transfer lead to in the fetus?
Decompensation
What can the fetus show signs of if there is placental or umbilical cord impairment?
Hypoxemia
What are possible placental causes leading to impairment in fetal oxygenation?
- Abruption (placenta tears away from wall of uterus)
- Infarction/ Blood Clot
- Placental being too small
- Increased placental resistance
These causes are not reversible
What are possible uterine causes leading to impairment in fetal oxygenation?
- Tachysystole
- Tetanic contraction
What are possible maternal causes leading to impairment in fetal oxygenation?
- Hypotension
- Hypoxia
Describe how fetal contractions are measured and what is considered a “normal” amount of contraction.
- Contractions quantified over 10-min period
- Averaged over 30 mins
- Less than or equal to 5 contractions in 10-min period
What is considered tachysystole?
> 5 contractions in 10-min period
What are the treatments for tachysystole?
- Stop Pitocin augmentation
- Nitroglycerine SL or IV to relax the uterus
- β-2 adrenergic receptor agonist (Terbutaline)
How is the mean FHR measured?
FHR is rounded to increments of 5 bpm during 10-min period
Normal FHR:
Tachycardia:
Bradycardia:
Normal FHR: 110-160 bpm
Tachycardia: >160 bpm
Bradycardia: <110 bpm
What are the fetal causes of tachycardia?
- Chorioamnionitis (Chorio) - infection from ruptured amniotic sac
- Sepsis
- Acute fetal hypoxia
- Fetal heart failure
- Fetal Anemia
What are the maternal causes of tachycardia?
- Maternal hyperthyroidism
- Maternal fever
- Epinephrine/ ephedrine
- β-2 adrenergic agonist (Ritodrine/ Terbutaline)
What are the causes of fetal bradycardia?
- Hypoxemia (initial response)
- Hypothermia
- Maternal hypotension (neuraxial block)
- Maternal hypoglycemia
- Fetal congenital heart block
What is considered a FHR acceleration?
- Increased FHR of at least 15 bpm lasting at least 15 seconds
- This is a sign of FHR variability
- Normal and Healthy
What is the single MOST IMPORTANT indicator of an adequately oxygenated fetus?
FHR Baseline Variability
What are the degrees of FHR Baseline Variability?
- Absent - amplitude range not detectable
- Minimal - detectable range but </= 5 bpm
- Moderate - amplitude range 6-25 bpm (happy place)
- Marked - amplitude range > 25 bpm
List the causes of decreased/ absent variability (long list)
- Arrhythmias
- Antenatal corticosteroids (betamethasone)
- BZD
- β-adrenergic antagonist
- Congenital anomalies
- Dexamethasone
- Ethanol
- Fetal sleep cycles
- General Anesthesia
- Hypoxemia (Severe)
- Magnesium Sulfate
- Pre-existing neurological abnormality
- Prematurity
- Promethazine
- Systemic opioid analgesia
What are the causes of increased/marked FHR variability?
- Fetal stimulation
- Mild/ Transient hypoxemia (umbilical cord compression in 2nd stage of labor)
- Maternal illicit drugs/ stimulants
What are the types of FHR Decelerations?
- Early
- Late
- Variable
- Can also be categorized as “Prolonged” or “Severe”
What is Early Deceleration?
- Symmetric gradual decrease in FHR with a return to baseline
- Onset of decel to nadir of FHR =/> 30 secs\
- Nadir of FHR deceleration is at peak of the contraction
What is the lowest point of FHR called?
Nadir
FHR decreases typically how many beats below baseline?
Typically <20 bpm (not always)
What is Early FHR Deceleration associated with?
- Uterine contraction (Benign)
- Vasovagal response to fetal head compression
How does fetal head compression cause Early FHR Deceleration?
- Pressure on fetal skull alters cerebral blood flow
- Vagus nerve stimulation
- Typically limited to active stage of labor
What does it mean if you see Early FHR Deceleration early in labor?
- Cephalopelvic
- Baby with big head
What kinds of shapes can be seen with Variable FHR Deceleration?
- Jagged and Irregular
- U, V, or W shape
What is a hallmark sign of Variable FHR Deceleration?
- Abrupt decrease in FHR and abrupt return to baseline
- Onset of decel to beginning of FHR nadair < 30 secs
- FHR decreases 15 bpm or more
- Last 15 seconds or longer but less than 2 mins
Frequent variable decels or variable decels occuring EARLY in labor can indicate what?
- Umbilical cord occlusion
- Need for operative delivery (C-section)
What can cause transient hypoxemia resulting in variable decelerations?
- Temporary cord compression (happens in most labors)
- If moderative variability/ acceleration present, likely ok
What are 3 causes of variable deceleration?
- Umbilical cord compression
- 2nd stage labor: fetal head compression (Dural stimulation → vagal discharge)
- Oligohydramnios (low amniotic fluid)
What is considered Severe Deceleration?
- FHR <70 bpm
- Decrease in FHR >60 bpm from baseline
- Associated with contractions duration >60 secs
What is the concern with minimal and absent variability?
Fetal Hypoxia
What is Late Deceleration?
- Symmetric gradual decrease in FHR with return to base line
- Begin after peak of contraction or after contraction is over
- Onset of deceleration to nadir of FHR =/> 30 secs (smooth and shallow)
What is Late Deceleration associated with?
- Uterine contractions
- Benign as long as variability is present
What are the causes of Late Deceleration (long list)?
- Hypoxemia
- Myocardial decompensation and failure
- Chorioamnionitis
- Post-term gestation
- Uterine hyperactivity
- Maternal hypotension/ hypertensive disorder
- Cardiac disease
- Maternal Smoking
- Maternal Anemia
- Placental abruption/ previa
What would you see on the fetal monitoring with continued hypoxia leading to lactic acidosis?
- Late Deceleration
- Fetal Tachycardia with minimal variability
What is the pathophysiology of Late Deceleration?
- Decreased O2 tension
- Sensed by chemoreceptors
- Vagal stimulation
- Decrease FHR
What is considered an ominous sign in fetal monitoring that might cause a mother to have a C-section?
Late deceleration with decrease/absent FHR variability
What are Prolonged Decelerations?
- Decrease in FHR >/= 15 bpm lasting 2 minutes or more but less than 10 minutes
- If decels last for >10 minutes, baseline change
Causes of Prolonged Deceleration.
- Umbilical cord compression
- Prolonged maternal hypotension/hypoxia
- Tetanic uterine contraction
- Prolonged head compression in 2nd stage of labor
What is a Sinusoidal Pattern?
Frequency?
Amplitude Range?
Time?
- Smooth, wave-like, undulating pattern
- Cycle frequency of 3-5 cycles per minute
- Amplitude Range of 5-15 bpm
- Persist > 20 minutes
- Requires obstetrical intervention
Causes of Sinusoidal Pattern
- Fetal anemia
- Rh Disease (incompatible blood)
- Severe hypoxia
What are the 3 FHR Tracing Categories and what are they indicative of?
- Category I: Normal fetal acid-base status
- Category II: Indeterminate
- Category III: Abnormal fetal acid-base status
Factors that indicate a Category I Tracing.
- Baseline FHR 110-160 bpm
- Moderate baseline variability
- No late or variable decelerations
- Early decelerations present/absent
- Accelerations present/absent
Factors that indicate a Category II Tracing.
- Fetal Tachycardia
- Absence of induced acceleration after fetal stimulation
- Prolonged deceleration > 2 mins but < 10 mins
- Recurrent late decels w/ moderate variability
- Not predictive of abnormal fetal acid-base status
Factors that indicate a Category III Tracing.
- Sinusoidal FHR pattern
- Absent FHR variability w/ recurrent late decels
- Recurrent variable decels
- Sustained bradycardia
Management of Category III Tracings
- Maternal position change
- D/c labor augmentation
- Treatment of tachysystole
- Surgical delivery
What is the method for neonatal assessment that is reproducible, standardized, and objective?
- Apgar Scoring System (Virginia Apgar 1953)
- Determine which neonates require resuscitation
What are the parameters of the Apgar Scoring System?
When are they performed?
- HR (0-2)
- Respiration Effort (0-2)
- Muscle Tone (0-2)
- Reflex Irritability (0-2)
- Color (0-2)
- Assess at 1 and 5 minutes after birth, 10 point scale
Apgar score for normal neonate
8-10
Apgar score for neonate with moderate impairment
4-7
Apgar score for neonate that needs immediate resuscitation
0-3
Risk for mortality is ___________ to 1 minute score
Inversely proportional
APGAR SCORE for HR
0:
1:
2:
APGAR SCORE for HR
0: Absent
1: <100 bpm
2: >100 bpm
APGAR SCORE for Respiratory Effort
0:
1:
2:
APGAR SCORE for Respiratory Effort
0: Absent
1: Irregular, slow, shallow, or gasping
2: Robust, crying
APGAR SCORE for Muscle Tone
0:
1:
2:
APGAR SCORE for Muscle Tone
0: Absent, limp
1: Some flexion of extremities
2: Active movements
APGAR SCORE for Reflex Irritability
0:
1:
2:
APGAR SCORE for Reflex Irritability
0: No response
1: Grimace
2: Active coughing and sneezing
APGAR SCORE for Color
0:
1:
2:
APGAR SCORE for Color
0: Cyanotic
1: Acrocyanotic (Trunk Pink, Extremities Blue)
2: Pink
