exchange of physiological nutrients and respiratory gases
waste elimination by fetus
How many umbilical arteries?
Umbilical veins?
2
1
Umbilical arteries flow to?
Placenta
Umbilical vein flows to?
Fetus
What is umbilical blood flow?
at term 120 ml / kg / min or about 360 ml / min
How are substances exchanged across the placental membrane (5 ways)?
diffusion, bulk flow, active transport, pinocytosis, breaks
What major substance(s) travels via diffusion?
Respiratory gases (CO2)
Fatty acids
Small ions
What major substance travels via bulk flow?
Water
via hydrostatic or osmotic gradient
What major substance travels via breaks?
Fetal Rh+ red cells can be exuded into the material circulation
What are the villi in the placenta?
Projections of fetal tissue
It is here that exchange takes place btw fetus and mom
What percent of uterine blood flow supplies the intervillous space and what percent supplies the myometrium?
80% intervillious space
20% myometrium
What compensatory mechanisms allow the fetus to survive for up to 10 minutes in the setting of O2 deprivation?
redistribution of fetal blood flow to brain, heart, and placenta
decreased O2 consumption
anaerobic metabolism
The fetal Hgb-O2 dissociation curve is shifted to the ____, meaning _____.
The maternal Hgb-O2 dissociation curve is shifted to the ____ right, meaning ______.
Left, fetal Hgb has a greater affinity for O2
Right, maternal Hgb has less of an affinity for O2
Fetal blood is (acidotic or alkalotic), while maternal blood is (acidotic or alkalotic).
Fetal blood= alkalotic (carries a lot of CO2 into the placenta which diffuse out and into the maternal blood)= left shifted
Maternal blood= acidotic (accepts CO2 from fetus)= right shifted
In simplest terms, the double Bohr effect:
encourages maternal blood to give up more O2 than is typical and more the fetus to take up for O2 than usual
Fetal hgb can carry as much as ___ to ___% more O2 can maternal Hgb. Is this a L or R shift?
20 to 30
LEFT SHIFT
T or F, Hgb can carry more O2 at a high PCO2?
F, Hgb can carry more O2 at a LOW PCO2
Maternal 2,3 DPG levels are (increased or decreased) to offset the effect of maternal hyperventilation.
increased, mom is RIGHT shifted
What type of Hgb makes up the majority of Hgb in the fetus?
Fetal Hgb
While interuterine, the _____ are non-functional and the liver is _____.
lungs
partly functional
How much of the fetal CO does the placenta receive?
50%
What is the goal of fetal circulation? How is this achieved?
Maximally perfuse the placenta and bypass nearly all of the nonfunctional lung and liver
Via anatomical shunts
Describe the path of fetal blood flow
Well oxygenated blood from the placenta, thru umbilical vein, ductus venosus (bypass liver), IVC, RA, thru FO, to LA, LV to brain and upper limbs
Deoxygenated blood from the SVC, to RA, RV, PA, DA (bypass lungs), descending aorta, to 2 umbilical arteries, to placenta for oxygenation
Why is the blood entering the RA from the SVC deoxygenated?
This blood has been used to perfuse the brain and upper body
Avg O2 sat of blood entering the RA from the IVC?
67%
Septum primum
Located on left side of the atrial septum that overlies the FO
Prevents blood from moving from LA to RA
At birth, fetal circulation shifts to adult circulation, the amount of SVR and PVR change to allow this. How do SVR and PVR change?
SVR INCREASES- due to loss of blood flow thru low rx placenta, increases pressures in LA and LV
PVR DECREASES- due to expansion of lungs with 1st breath, VD occurs, this reduces PA, RA, and RV pressures
Negative intrathoracic pressures in the newborn's 1st breath equal
40-60 cm H20
How does the FO close?
Due to the pressure changes in the heart
Low right sided pressures and high left sided pressures
T or F, even if permanent anatomic closure does not occur the higher left vs. right sided pressures keep the FO closed?
T
How does the DA close?
DA constricts due to increased O2 in the area (blood backflows from aorta into the DA)
Flow stops within 1-8 days
What happens if the DA does not close?
Elevated PA pressures (due to backflow from LV to aorta thru DA to pulmonary arteries)
How does the DV close?
Blood flow from the umbilical vein ceases and the muscular walls of the DV contract
Not really sure exactly why it closes
Persistent pulmonary hypertension
persistent fetal circulation
occurs due to acidosis or hypoxia in the 1st days of life
R to L shunt occurs across the FO or the DA which causes hypoxia and acidosis, which then causes more shunting
a vicious cycle is created
What pressure change will cause a R to L shunt in the newborn?
Anything that causes PVR to exceed SVR
What 3 diseases are included in PIH?
pre-eclampsia
eclampsia
HELLP syndrome
In what pts is PIH most commonly seen in?
Primigravidas, < 20 yo
What BP is considered PIH?
SBP > 140 and SBP >90
Potential complications of PIH?
ARF, cerebral hemorrhage, and pulmonary edema
HELLP
Hemolytic Elevated Liver enzymes
Low Platelets
When does pre-eclampsia typically occur?
After the 20th week of gestation
Describe the patho of pre-eclampsia
Hyperdynamic CV state
Increased CO
Generalized VC
Overall decreased plasma volume (compared to normal parturient)= hypovolemia
SQ tissue edema is common
How can PIH lead to HELLP
Get tissue hypoxia due to VC
Renal and hepatic dysfunction can result
How is uterine activity affected in pre-eclampsia?
Increased, uterus can become hyperactive and markedly sensitive to oxytocin
Why is proteinuria seen in pre-eclampsia?
Due to decreased GFR
Eclampsia
Severe pre-eclampsia marked by seizures / CNS involvement
Priority in the PIH pt
Control symptoms associated with end organ involvement
Priority in the eclamptic pt
Control convulsions (increased O2 consumption)
T or F, maternal mortality is unaffected by the number of convulsions?
F, mortality increases with the number of convulsions
How are convulsions controlled?
Mg 2-4 g
Benzos- valium 2-5 mg, versed 1-4 mg
Barbs- thiopental 50-100 mg
GA if unable to control seizures to protect airway and deliver the fetus
HELLP cause
unknown
Issues associated with HELLP
Activation of the coagulation cascade
Hemolytic anemia
Destruction of Plts
Liver suffers portal necrosis / ischemia resulting in elevated LFTs
S/sx of HELLP
Gradual
H/A, blurred vision, N/V, "band pain" around upper abdomen, tingling in extremities, HTN
T or F, HELLP can also present after delivery?
T
Definitive tx for PIH
delivery of fetus and placenta
control of disease process if fetus is too immature to be delivered
What does tocolytic mean?
Stops uterine contractions
Mg
anti-sz agent, tocolytic, mild general VD
Lowers maternal BP and improves uterine blood flow
Mg SE
abn neuromuscular transmission (can result in maternal weakness- including respiratory insufficiency)
T or F, hydralazine, BB, and CCB benefit mom and fetus in the tx of PIH?
F, benefit mom, but do not appear to improve fetal outcome
Can LEA be converted to provide analgesia for C-section?
Yes, give 1-2 L prior for expected T4 level
LEA level
T10
Why might a parturient with PIH have a difficult airway?
Airway edema is exacerbated
Can ketamine be used for induction for an emergency C-section for a pt with PIH?
NO, will further increase BP
Considerations regarding propofol, NDMR, succ for emergency section in PIH pt
Reduced doses of propofol
Defasciculating doses of NDMR are unnecessary (previous Mg use)
Succ 1.5 mg / kg
Volatile agent dosing for emergency section for PIH pt
1.5 MAC for 1st minute then 2/3 to 1/2 MAC
T or F, the use of ST low concentrations of inhalational agents are not associated with decreased uterine activity, increased uterine bleeding, or neonatal depression
T
Risks associated with neonate born to PIH mom
Higher risk for prematurity
Usually SGA
Higher risk asphyxiation, drug depression, and meconium aspiration
Why is close monitoring of the postpartum PIH mom needed for 24-48 hours?
Prone to convulse or develop pulm edema with 24 hours of delivery
