Ureteroplacental Part 2 Flashcards
Fetal circulation involves blood running ________, whereas adult circulation involves blood running in ________.
parallel : series
How does fetal circulation differ from adult circulation? (3)
Fetal circulation runs parallel (adult runs in series right side/left side)
Specialized vessels
-Foramen Ovale, Ductus arteriosis/venosus
Shunting
R → L shunt (bypassing underdeveloped fetal lungs)
What are the differences between parallel and series blood flow?
Parallel:
-both right and left sides of the fetal heart provide systemic blood flow.
Series:
-right side of heart provides pulmonary blood flow
-left side provides systemic blood flow
Are the SVR and PVR increased or decreased in fetal circulation? Why?
SVR is LOW in fetus
-placenta has low resistance vascular bed
PVR is HIGH in fetus
-fetal lungs collapsed and fluid filled
-very minimal pulmonary circulation
Why are the fetal lungs mostly bypassed in fetal circulation? Where is the main site of oxygen exchange for the fetus?
Lungs are under developed in the fetus (high PVR)
Placenta is the site of oxygen exchange for fetus (not the lungs)
What are the three anatomic communication of fetal circulation?
- Ductus Venosus
- Foramen Ovale
- Ductus Arteriosus
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).
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.
Which vessel connecting pulmonary artery to descending aorta, diverts blood away from underdeveloped lungs?
Ductus Arteriosus
What vessel carries oxygenated blood from the placenta to the fetus?
Umbilical Vein (80-85% saturated)
How is the blood from the umbilical vein dispersed?
- 50% to fetal portal circulation (Liver/stomach etc)
- 50% bypasses fetal portal circulation through Ductus venosus and into IVC.
The percentage of umbilical vein blood directed to the liver will increase in conjunction with ______ ____.
gestational age
What happens to the oxygenated blood that is diverted into the inferior vena cava via the ductus venosus?
-Mixes with small amount of deoxygenated blood returning from fetus’ lower body
-Mixed blood returns to Right atrium
(also mixed with blood returning from upper body via SVC)
What is the importance of blood in the Right Atrium passing through Foramen Ovale directly to the Left atria?
Foramen Ovale shunt:
Bypasses immature lungs
-this conserves energy
Optimizes O2 delivery to fetal heart/brain
Describe the path for most of the blood through fetal circulation.
RA → FO → LA → LV → Ascending Aorta → systemic circulation.
What percentage of blood goes from the RA to the RV and subsequently perfuses the lungs? Where does a majority of this blood flow after entering pulmonary artery?
10% of RA blood to RV.
~90% passes through PA → ductus arteriosus →descending aorta →perfusing lower body of fetus
“Ductus arteriosus (DA) to descending aorta (DA)”
Describe the fetal circulation Right → Left Shunt?
What portion of the autonomic nervous system develops first and is predominant throughout fetal life?
Parasympathetic system
What are the main environmental factors affecting fetal baroreceptors and thus SNS output?
Baroreceptors in aortic arch and carotid arteries sense : Maternal BP & stress
When does respiratory effort begin after delivery?
30 - 90 seconds typically
What respiratory changes occur at birth?
- ↓ Intrathoracic pressure l/t Air entering lungs
- 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 (↓ R→ L Shunt)
↑ pulmonary blood flow
What does surfactant do?
↓ surface tension = prevention of alveolar collapse
When does surfactant production start? What can be given to assist with surfactant production in neonates born before surfactant production complete?
24 - 28 weeks gestation
*Pre-term birth before production complete can be given steroids to assist with surfactant production
The ____ will constrict and close due to increased O₂ levels.
Ductus arteriosus
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
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?
- Hypoxia
- Acidosis
- Hypovolemia
- Hypothermia
What things can lead to premature constriction of the Ductus Arteriosus?
- NSAIDs
- Preterm births
- ↑ PA pressure
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.
- ↑ Adenosine accumulation = cerebral vasodilation
Why does a fetus have bradycardia in response to hypoxia?
In response to Hypoxia:
-chemoreceptor stimulation → peripheral vasoconstriction
-Vagal response → bradycardia
These mechanisms l/t:
-Increases amount of blood shunted through Ductus Venous
-Increased O2 delivery to heart and brain
Where is more blood shunted in the event of fetal hypoxia?
DV = ↑O₂ delivery to heart & brain
What is the fetal response to prolonged hypoxia (more than just a few minutes)?
SNS activates
-catecholamine secretion
-fetal tachycardia
Longer periods of hypoxia → fetal demise
What are the results of chronic fetal hypoxia (weeks or months)?
- Fetal growth restriction
- Impaired brain and kidney function
- Cardiomyocyte apoptosis
- Fetal demise
all results of depleted reserves
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 ________. What are the limitations of this type of monitoring?
TOCO
Limitations:
-measures only Contraction Frequency (cannot measure contraction strength)
-FHR strip will have mmHg on Y axis, however this is an approximation
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?
Placental reserve
Similar to swimmer relying on Cardiopulmonary reserve when underwater.
What are some placental causes of impaired fetal oxygenation that are unlikely to be reversible?
- Abruption (placenta tears away from uterine wall)
- Infarction/blood clot in placenta
- Too small of a placenta (doesn’t grow in proportion to fetal growth)
- ↑ placental resistance (only reversible if d/t contraction)
What are the two problems with the uterus that result in fetal oxygenation impairment?
- Tachysystole (excessive uterine contraction)
- Tetanic Contraction (caused by maternal stress, pitocin, meth/cocaine abuse)
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
How are uterine contractions measured on a TOCO strip?
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
What do the bold vertical lines represent in a FHR strip? What do the small boxes between these lines represent?
Bold vertical lines represent 1 minute
Each small box represents 10 seconds
-6 boxes between each line for total of 60 seconds
What drugs are utilized to treat tachysystole?
- Stop Pitocin gtt (if running)
- Nitroglycerin (sublingual or IV)
- Terbutaline (β2 agonist)
Terbutaline can lead to tachysytole in rare instances
How is a baseline FHR calculated?
Mean FHR over 10 minute period; rounded by increments of 5bpm
What is the normal FHR range?
What defines FHR tachycardia?
Bradycardia?
- Normal: 110 - 160 bpm
- 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/infection
- Epi / ephedrine
- β2 agonists (Ritodrine, terbutaline)
terbutaline may cause tachysystole in high doses d/t transient β1 stimulation
What are the common causes of fetal bradycardia?
- Hypoxemia initial response to bradycardia (umbilical compression or fetal head compression)
- Hypothermia
- Maternal HoTN (may be secondary to neuraxial anesthesia)
- Maternal hypoglycemia
- Congenital heart block
What are FHR accelerations?
“15x15”
Periods of increased FHR
- Increase HR of at least 15 bpm
- lasts at least 15 seconds
Is it a good sign if the OB is able to induce fetal heart rate accelerations?
Yes!
FHR accelerations indicate:
- sign of FHR variability
- normal and healthy fetus
inducing FHR accelerations assesses fetal well being (able to compensate to stimulation)
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 Ideal range
- Marked: range > 25bpm
There are a lot of things that can cause decreased or absent FHR variability. Which one is normal?
- Fetal sleep cycles
*this is why OB will stimulate to assess well being. (fetus may be sleeping and have low or no variability)
What are some medications that can lead to minimal/absent variability?
Dexamethasone
Benzos
Magnesium sulfate
Systemic Opioids
Promethazine
What are some common causes of marked FHR variability?
- Fetal stimulation
- Transient hypoxemia (umbilical cord compression in 2nd labor)
- Maternal drug use (stimulants)
What are FHR decelerations? What are the three types of FHR decelerations?
Temporary drops in FHR
- 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? What are the characteristics of early decelerations and what are they associated with?
- Symmetric gradual decrease in FHR with return to baseline.
- Onset of Deceleration to nadir (lowest point): ≥ 30 seconds
- FHR decreases typically < 20 bpm
associated with uterine contraction and are benign
What is the physiologic cause of benign early decelerations?
Vasovagal response to fetal head compression
↳↓CBF from pressure on skull 2° to uterine contraction.
↳vagus stimulation (CTX pressure ↑/HR ↓)
if early in labor fetal head may be large compared to pelvis
Early decelerations are more typical during the _____ stage of labor.
active
What are some characteristics of variable decelerations?
Varying: onset, depth and duration w/ contractions
Shape: jagged/irregular U, V, W shape
Abrupt ↓FHR and Abrupt return to baseline
What type of deceleration is depicted below?
Variable decelerations
What is the onset and duration seen with Variable Decelerations?
Onset of decel to beginning of FHR Nadir < 30 seconds
Duration: lasts ≥ 15 seconds but < 2 minutes
What is the most common cause of variable decelerations? Is moderate variability a cause for concern?
Transient Hypoxemia
- Temporary cord compression (happens during most labors).
- 2ⁿᵈ stage of labor (fetal head compression)
Moderate variable decels in the presence of Accelerations are usually okay.
Frequent variable decelerations or variable decelerations occurring early in labor are often an indicator for what? What is the significance of this finding?
Umbilical cord occlusion
Indicative for operative delivery.
What is oligohydramnios? What can this condition lead to?
Low volumes of amniotic fluid
- Oligohydramnios is another cause of Variable decelerations
What characterizes severe decelerations? What does severe decels indicate?
- FHR < 70 bpm
- ↓ in FHR > 60 bpm from baseline
Indicates fetus not tolerating contractions well
What can cause severe decelerations?
Contractions lasting longer than 60 seconds which l/t:
-decreased umbilical blood flow
-impaired fetal cardiac output
Severe decelerations + minimal/absent FHR variability should be concerning for what?
Hypoxemia
Continued Hypoxia → lactic acidosis
What are the characteristics of late decelerations?
Symmetric/gradual decrease in FHR with return to baseline
-occur after peak of contraction (or after contraction is over)
Onset of decel to nadir of FHR: ≥ 30 seconds (smooth and shallow)
Late decelerations are associated with _____ ______ and can be benign as long as _______ is present.
Uterine contractions: variability
What type of decelerations are depicted below?
Late decelerations
What type of decelerations are depicted below?
Late decelerations
What are some non-benign causes of late decelerations?
- Hypoxemia
- Myocardial decompensation/failure
- Chorioamnioitis
- Post-term gestation
What are some causes of late decelerations that are related to poor maternal health?
- Uterine hyperactivity
- Maternal HoTN/HTN
- Smoking
- Anemia
- Placental abruption/previa
How would hypoxemia present alongside late decelerations?
Continued hypoxia → lactic acidosis presents as:
Late decels + fetal tachycardia w/ minimal/absent variability
What is the underlying mechanics behind late decelerations?
Delayed onset of deceleration r/t decreased O2 tension:
Decreased O2 tension
↳sensed by fetal chemoreceptors
↳vagal stimulation
↳ decreased FHR
When are late decelerations considered an ominous sign for fetal survival?
Late decelerations w/ decreased/absent FHR variability is an ominous sign.
What is the duration and FHR change seen with Prolonged Decelerations?
FHR change: decrease in FHR ≥ 15bpm
Duration: lasting > 2 minutes; <10 mins
What consideration is made for decelerations lasting longer than 10 mins?
Decels lasting >10 mins constitutes a change in FHR baseline.
FHR averaged over 10 minutes. Greater than 10 mins = new baseline
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
What type of FHR tracing is exhibited below?
Sinusoidal pattern
What are the characteristics of Sinusoidal pattern? Include appearance, frequency, amplitude and duration.
Rare but ominous pattern
Smooth/wave-like, undulating pattern (no variability)
Cycle frequency: 3-5 cycles per minute (times the wave like pattern repeats per min)
Amplitude range: 5-15 bpm
Duration: > 20 minutes
What does persistent sinusoidal FHR tracings indicate?
This is an ominous pattern that requires Obstetric intervention
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? What does this mean for anesthesia?
Category I:
-indicates no need for emergent delivery
What are characteristics of Category I FHR tracings?
- Baseline FHR 110 - 160 bpm
- Moderate FHR variability
- No late/variable decels
- early decels: present or absent
- accelerations: present or absent
What are the characteristics of Category II of FHR tracings?
Category II: indeterminate (worried but no emergent delivery)
- Fetal tachycardia
- Absence of induced accelerations w/ fetal stimulation
- Prolonged decels > 2min but < 10min
- Recurrent late decels w/ moderate variability
not predictive of abnorml fetal acid-base status
What are the characteristics of Category III of FHR tracings?
Category III: abnormal fetal acid-base status (c/s likely)
- Sinusoidal FHR pattern
- Absent FHR variability w/ recurrent late decels
- Recurrent variable decels
- Sustained fetal bradycardia
predictive for abnormal fetal acid-base status
What are some things that can be done to address Category III FHR tracings?
- Maternal position change
- Discontinue pitocin
- Treat tachysystole
- Surgical delivery
What are the five components of the Apgar scoring system?
- HR
- Respiratory effort
- Muscle tone
- Reflex irritability
- Color
What are the Apgar score ranges for normal, moderate impairment and immediate neonate resuscitation?
Normal: 8 - 10
Moderate impairment: 4-7
Immediate Resuscitation: 0-3
Discuss the Apgar scores based on the table presented in lecture
Risk for neonate mortality is __________ proportional to the apgar 1 minute score.
inversely
Lower score = higher risk of mortality
