Flashcards in Exam 1B: Uteroplacental Blood Flow Deck (88):
Fetal circulation travels to the placenta through ____ that divide into smaller vessels within the _____.
2 umbilical arteries (de-o2 blood) ...... fetal villi
This is where EXCHANGE (not mix) occurs between maternal and fetal blood.
Capillaries at the tip of the chorionic villi (intervillous space)
1. This vessel carries nutrient rich blood to the fetus.
2. What is the O2 sat of the blood carried by number 1?
3. O2 sat of number 1 after passing certain fetal shunts.
1. Umbilical vein
As blood travels past the _____, some of the enriched blood goes to the LIVER, but most empties directly into the ____ where it mixes with deoxygenated blood returning from the lower extremities, pelvis, and kidneys.
ductus venosus...... inferior vena cava
As blood from the inferior vena cava enters the right atrium, a large portion of it is shunted directly into the left atrium through the _____. A small valve, the _______, prevents blood from moving in reverse direction.
foramen ovale ....... septum primum
These 2 are supplied with most oxygenated blood. Why?
Myocardium and brain since the coronary and carotid arteries are the first to branch from the ascending aorta.
What structures close after the infant takes its first breath after delivery?
foramen ovale and ductus arteriosus
This is the metabolically active part of the placenta.
Three microscopic tissue layers found in placental membrane.
1. Fetal trophoblasts (Cytotrophoblast, Syncytiotrophoblast)
2. Fetal connective tissue (supports the villi)
3. Endothelium of the fetal capillaries
Uterine blood flow (UBF) rises progressively throughout pregnancy and at TERM is ___% of the maternal cardiac output (which is ___ml/min)
10% ..... 700 ml/min
How many percent of UBF go to the intervillous space (placenta)
Placental vasculature normally exists in a ______ state.
UBF is not auto regulated.
1. UBF is proportional to the ____.
2. UBF is indirectly proportional to _____
1. mean perfusion pressure
2. Uterine vascular resistance
Factors that affect UBF (3)
1. Uterine arterial pressure
2. Uterine venous pressure
3. Uterine vascular resistance
Management to prevent vena caval compression.
Left uterine displacement
Vomiting can DECREASE uterine perfusion pressure
These (2) hormones are secreted in an attempt to maintain systemic BP increase uterine vascular resistance.
Angiotensin II and Vasopressin
Maternal blood is carried by the _______ to placental site which divides into spiral arteries in the basal plate.
uterine and ovarian arteries
Blood delivered to uterus and placenta is determined by ____
Exchange of blood takes place with fetal blood as maternal blood passes the fetal villi toward the ____.
Maternal blood drains back to the veins in the ______ and return to the maternal vasculature.
This occurs when a drug is in lipid-soluble form and crosses the cell membrane.
Ion trapping. (fetal blood is slightly acidotic --> drug becomes ionized)
Placental transfer of drugs: Increased free drug = increase amount of transfer
This is the most common process of transfer of substances from maternal to fetal circulation and vice versa
Highly water soluble drugs, such as _____, do not pass placenta in significant amounts.
This is the diffusion of a drug from an area of higher concentration to an area of lower concentration.
This governs the rate of transfer of a drug across a membrane
What is the most important factor in determining the rate of diffusion of a drug across a cell membrane?
Concentration gradient of the drug
This affects the diffusion coefficient (K) in Fick's equation.
1. This mode of transport requires a carrier to make the transport more efficient.
2. Name 2 substances transported
1. Facilitated Diffusion / Carrier-mediated transport
2. Glucose and Lactic acid
Which crosses the placenta more easily, drugs that bind to albumin or drugs that bind to alpha-1 acid glycoprotein?
Drugs that bind to albumin because they have lower binding affinity. Alpha-1 acid glycoprotein bind the drugs "tightly" therefore less drug is released.
This is the less frequent mechanism of transport, but responsible for the transfer of very important substances.. It requires energy due to transport against concentration gradient.
Movement of a substance against its concentration gradient via a specific protein carrier, which uses the energy ATP to drive transport.
Primary Active Transport
Movement of one transport substrate down to its gradient via a carrier protein.
Secondary active transport (Na entry into cell)
It is a process that requires energy and is usually faster than passive transport. It often involves the combination of the drug with a carrier molecule that is capable of transporting the drug across a membrane even if it is against a concentration gradient.
This allow for the transfer of fetal Rh + blood deposited in Rh negative mother. Villi break off within the intervillous space, and the contents may be extruded into the maternal circulation and vice versa.
Breaks (Accidental mixing of blood)
This transport mechanism requires cellular energy. Cell membrane invaginated around the MACROmolecule.
Pinocytosis (explains the maternal-fetal transfer of immunization IgG)
Placental (fetal) and intervillous (maternal) blood flows depend on _______ on both sides of membrane.
BP and contractile status of vessels
Describe the baby's O2-Hgb dissociation curve.
It is shifted to the left of the maternal O2-Hgb curve. It will have a greater affinity to oxygen.
1. The fetal blood has a HIGHER Hgb concentration than does maternal blood.
2. Fetal placental blood flow than maternal placental blood flow are EQUAL
3. Fetal blood has LOWERpH than does maternal blood.
This term denotes the blood oxygen tension (PaO2) that produces 50% saturation of erythrocyte Hgb.
1. What is the P50 value of fetal blood?
2. What is the P50 value of adult blood?
1. 19 - 21 mmHg (75-85% of fetal blood is Hgb F). Thus, fetal hgb has a higher affinity for O2 than maternal Hgb.
2. 27 mmHg
What curve denotes that the hgb binds more tightly.
What is the fetal Hgb? Maternal Hgb?
Fetal: 15g/ dl, Maternal: 12g/ dl
What will happen when there is significant lack of O2 in fetus? (4)
1. Decreased fetal O2 consumption
2. Redistribute blood flow
3. Will lead to lactic production and metabolic acidosis
What are the effects of maternal hypocapnea on the fetus? (2)
fetal hypoxia and acidosis due to vasoconstriction, decreased venous return, and left shift of the maternal O2 dissociation curve.
Hypocapnea is usually the result of
hyperventilation and increased intrathoracic pressure
What are the two most important components of placental exchange?
1. Rates of blood flow on each side of the placenta
2. Area available for exchange
Name 4 factors which could cause a decline in perfusion pressure or increase uterine vascular resistance.
3. Endogenous or exogenous vasoconstriction
Pain relief is the core mechanism by which regional anesthesia may INCREASE uterine blood flow. Acute stress increases plasma norepi ___% and decreases UBF ___%
25% ..... 50%
Regional anesthesia may DECREASE UBF as a result of maternal hypotension. How? (3)
1. Decreased perfusion pressure
2. Stimulation of release of endogenous vasoconstrictors
3. Unintentional IV injection of meds intended for epidural space.
IV eli when given as test dose can reduce UBF as much as ____ for 3 mins.
Seem to have MINIMAL direct effect on UBF. Reduction in systemic arterial pressure resulting in decreased uterine perfusion pressure.
Rapid uptake and distribution, leading to fast maternal-fetal balance with a fast decrease in fetal blood after birth. This is better than Thiopental at blunting hypertensive response to DL and intubation.
This drug may have sedative effects on the neonate, resulting in lower 1 and 5 minute APGARs than with thiopental.
When do you give versed?
after the baby is out
This induction drug may result in hypertension and tachycardia. This is especially helpful in patients with decreased IV volume. It will maintain UBF.
Halogenated inhalation agents are potent UTERINE relaxant. They are used for (7)
1. Version and extraction
2. Breech delivery
3. Retained placenta/ Placenta abruption
4. tetanic contractions
5. Surgical manipulations
6. hyper stimulation with oxytocin
7. Cocaine overdose
At what MAC will not change the UBF?
< 1 MAC (all agents are similar)
At what MAC will prevent bleeding in C/S?
< 0.5 MAC
This inhalational agent is detectable in both umbilical venous blood and arterial blood within 1 minute.
How is MAC affected by pregnancy?
MAC decreases by 2nd or 3rd months of gestation due to effects of progesterone.
Use of this drugs in epidural have no effect on UBF (2)
fentanyl and morphine.
At 50 mcg of this drug, when given epidurally, will decrease maternal MAP but not alter the uterine blood velocity waveform indices in laboring women.
These drugs are associated with hypotension when given spinal.
Demerol and sufenta
This drug when given spinal has low placental tissue content and fast washout.
(Concurrent NArcan apparently doesn't affect placental transfer of Morphine)
What do you suspect if you don't see hypotension post spinal?
IV drug which can be detected in umbilical venous blood as soon as 90 seconds after maternal administration.
This IV opioid when given before CS gives excessive maternal sedation without adverse neonatal effects.
Timing is important in IV drugs. Consider timing of ___- vs ____.
highest peak concentration vs delivery of infant.
Maternal administration of muscle relaxants rarely affects neonatal muscle tone at delivery because ____ (2)
it is highly ionized and has high molecular weight
Sux doses larger than ____ are required before the drug can be detected in umbilical venous blood.
> 300 mg
Neonatal neuromuscular blockade can occur when high doses are given repeatedly or when the fetus has ___
1. These 2 anticholinergics cross the placenta easily
2. Which one is poorly transferred?
1. atropine and scopolamine
Quartenary ammonium compounds undergo LIMITED transplacental transfer. Maternal administration of neostigmine does not reverse atropine-induced fetal tachycardia.
What is the preferred anti cholinesterase/ anticholinergic mix?
Neostigmine + Atropine (because atropine can cross and will treat fetal bradycardia)
1. Epinephrine, frequently mixed with LA, has NO evidenced effect on intervillous blood flow.
2. Clonidine contains warning against epidural use --> vasoconstriction and hypotension.
T and T
1. More likely to increase BP by increasing cardiac output with less direct vasoconstriction
2. Safe given in small doses that are titrated to effect.
1. Ephedrine (preferred; it has longer duration than epinephrine)
This anticoagulant is CONTRAINDICATED because it can cause fetal loss and congenital anomalies
Which anticoagulants don't cross the placenta?
Regional anesthetics cross the placenta very easily, but when max recommended doses are respected, there is a good maternal and fetal tolerance.
How / when do local anesthetics affect uterine blood flow?
1. inadvertent IV injection of local anesthetic
2. Paracervical block
_____exerts greater vasoconstrictor effect than either chlorprocaine or lidocaine.
2 anti-HTN meds that decrease BP while increasing UBF
Hydralazine and Nitroglycerine
This anti-HTN does not alter UBF
This antiHTN inhibit uterine contractility, will slow AV conduction and will produce arteriolar vasodilation.
Hypo or hyper ventilation:
Occurs during painful contractions or increased vent setting. This alone can decrease UBF.