Test 2: Uteroplacental & Fetal Physiology Part 1 (Slides 1 - 44) Flashcards
What does the acronym UBF stand for?
Uterine Blood Flow
What does the acronym IUGR stand for?
Intrauterine Growth Restriction
What does the acronym PIH stand for?
Pregnancy Induced Hypertension
What is Gravida?
Number of Pregnancies
What is Para?
Number of live births (>20 weeks)
What is P50?
Oxygen level at which hemoglobin is 50% saturated
What is HbF?
Fetal Hemoglobin
What is HbA?
Adult Hemoglobin
What is one of the most important determinants of maternal/fetal gas exchange?
Uterine Perfusion
Uterine Perfusion Increases throughout gestation
What is the UBF at term?
UBF makes up what percent of total maternal cardiac output?
- 700 ml/min
- 12% of total maternal CO
What accounts for the low resistance of uterine perfusion?
Systemic Vasodilation
What makes the high blood flow of uterine perfusion?
- Increase blood volume
- Increase CO
When is the uterine arterial bed maximally dilated?
At term
What is the primary source of UBF?
What is the secondary source of UBF?
- Primary Source: Uterine Artery
- Secondary Source: Ovarian Artery
Where does the Uterine Artery branch from?
Internal iliac (hypogastric) arteries
Where does the Ovarian Artery branch from?
Aorta at L4 Level
70-90% of uterine blood passes through the _______ space.
Intervillous space
What is the intervillous space of the placenta?
- Large sinus w/ multiple folds that act on the fetal-maternal interface, where maternal blood enters to provide nutrients and gas exchange.
- Low resistance system
The intervillous space accommodates _______ mL of maternal blood.
350 mL
Blood enters the intervillous space via ______.
Spiral Arteries
What is the equation for UBF?
Uterine Perfusion Pressure / Uterine Vascular Resistance
What is the equation for Uterine Perfusion Pressure?
Uterine arterial pressure - Uterine venous pressure
Is there autoregulation of UBF in pregnancy?
What is UBF dependent on?
- No
- UBF is dependent on maternal blood pressure
What protective mechanism is in place for fetal oxygenation?
UBF exceeds the minimal demand for fetal oxygenation
What are the three causes of Decreased UBF?
- Decreased Uterine Arterial Pressure (UAP)
- Increase Uterine Venous Pressure (UVP)
- Increase Uterine Vascular Resistance (UVR)
What factors can decrease Uterine Arterial Pressure?
- Supine Position (Aortocaval Compression)
- Hypovolemia (Dehydration or Hemorrhage)
- Hypotension (Drugs, Neuraxial Anes, or Bleed)
How does Neuraxial Anesthesia cause hypotension?
Sympathetic blockade
It is important to get ahead and treat hypotension (fluid bolus before neuraxial anesthesia)
What drugs used in anesthesia can cause maternal hypotension?
- Propofol, VA
- Magnesium (Often given to treat pre-eclampsia)
- Opioids
What are the treatments for maternal hypotension?
- Vasopressors
- Fluid bolus
What happens to Uterine Arterial Pressure if there is a decrease in Maternal Blood Pressure?
Decrease Uterine Arterial Pressure
This will result in decrease Uterine Profusion Pressure and decrease UBF
What are the factors that increase Uterine Venous Pressure?
- Supine position (IVC Compression)
- Contractions
- Drug-induced tachysytole
- Pushing efforts
- Seizures
How are UBF and contraction strength related?
- UBF is inversely related to contraction strength
- ↑ Contraction Strength = ↓ UBF (vice versa)
What is tachysystole?
- A high amount of contraction over a short period
- 5 contractions over 10 minutes for 2 consecutive intervals
What is Hyperemia?
When does it occur?
- Excess of blood in the vessels supplying an organ or other part of the body.
- Hyperemia occurs during uterine relaxation.
What drugs can cause tachysystole?
- Oxytocin
- Cocaine
- Methamphetamine
What are factors that can increase Uterine Vascular Resistance?
- Endogenous Vasoconstrictors (Catecholamines triggered by stress response or hypotension)
- Exogenous Catecholamines (Neo, Ephedrine)
- High concentration of Local Anesthetic
What vasopressor crosses the placenta and increases fetal metabolic requirements?
Ephedrine
Has been shown to decrease fetal pH, base excess, and umbilical O2 content
What is the vasopressor of choice if repeated doses are needed?
Phenylephrine
How does a high concentration of local anesthetic increase Uterine Vascular Resistance?
- Arterial Constriction
- Inhibition of endothelium-mediated vasodilation
- Stimulation of myometrial contraction
How does epinephrine affect the UBF for healthy parturients receiving neuraxial analgesia/anesthesia (epi wash)?
No change in UBF
If Epi is administered IV, there will be a DECREASE in UBF
Why is epinephrine used in neuraxial anesthesia?
Epi increases the duration of action of neuraxial anesthesia.
What is the test dose of epinephrine used in neuraxial anesthesia?
10-15 mcg
Effects of clonidine and dexmedetomidine as adjunct agents in neuraxial anesthesia.
Clonidine and dexmedetomidine are alpha2-adrenergic agonists that can potentiate analgesia when added to epidural solutions.
Clonidine and Precedex effect on UBF if given epidurally.
Clonidine and Precedex effect on UBF if given IV.
- Epidural: No change in UBF
- IV: Decrease in UBF
High doses of IV clonidine and dexmedetomidine can have what effect on Uterine Vascular Resistance?
Increase UVR d/t vasoconstriction
How does neuraxial anesthesia increase UBF?
- Decrease circulating catecholamines
- Pain control
How does hypotension secondary to neuraxial anesthesia affect uterine arterial pressure?
Decrease UAP
When will neuraxial anesthesia INCREASE UBF?
- Increases UBF when hypotension is avoided
When will neuraxial anesthesia DECREASE UBF?
- Decrease UBF when hypotension is present
- Sympathectomy → Peripheral Vasodilation → Hypotension → Decrease UBF
How does magnesium sulfate increase UBF?
- Relaxation of smooth muscles
- Vasodilation
**Mag can either increase or decrease uterine blood flow
**Dr. Freeman said this concept will not be tested
How does hydralazine increase UBF?
- Direct relaxation of arterioles
At what MAC range will volatile anesthetic have minimal effect on UBF?
0.5 - 1.5 MAC
Increased MAC will decrease CO and BP will decrease UBF as a result of decrease UAP.
What is the effect of increased MAC on Uterine Arterial Pressure?
- Decrease UAP
What is the yellow side of the placenta called?
What is the purple side of the placenta called?
- Yellow Side: Chorionic Plate (Fetal Side)
- Purple Side: Basal Plate (Maternal Side)
The placenta grows in proportion to the ________
Fetus
Name the four functions of the placenta.
- Production of proteins, hormones, & enzymes
- Gas Exchange
- Nutrient & Waste exchange
- Drug & Toxin transfer can occur
The umbilical cord usually contains how many arteries and veins?
- 2 Arteries
- 1 Vein
2 Arts (Hearts) make 1 Vein-by (Baby)
What structure will deliver oxygenated blood to the fetus?
- Umbilical Vein
What structure will take de-oxygenated blood away from the fetus to the placenta?
- Umbilical Arteries
The two-way substance transfer in the intervillous space depends on what three factors?
- Concentration gradient
- Permeability
- Restriction of movement (Some substances are bound w/i placental tissue, minimize fetal exposure and accumulation)
Describethe movement of oxygen in the intervillous space
Oxygen moves down the concentration gradient from the pool of maternal blood in intervillous space into fetal capillaries.
Describe the movement of CO2 in the intervillous space
CO2 moves down the concentration gradient from the fetal circulation into maternal blood.
What are the four transfer mechanisms of the placenta?
- Passive Diffusion
- Facilitated Diffusion
- Active Transport
- Pinocytosis
What is Passive Diffusion?
Movement along a concentration gradient without the use of ATP.
Examples: O2, CO2, and most anesthestic drugs
What is Facilitated Diffusion?
Movement with the help of carrier proteins, still following concentration gradient
Example: Glucose
Follows saturation kinetics
Increase Temp, Increases Transfer
What is Active Transport?
Movement against the concentration gradient requiring energy (ATP)
Example: Na+, K+, Ca2+
What is Pinocytosis?
- Cellular engulfment
- Transfer of large macromolecules requiring energy.
- Requires membrane rearrangement and vesicle formation
Example: Transfer of Immunoglobulin G from mother to fetus
What are the five main pharmacokinetic factors that impact drug transfer across the placenta?
- Blood flow
- Lipid solubility
- Protein binding
- pKa and pH change
- Size of Molecule
Honorable Mentions: Gestational age, maternal factors, drug metabolism in placenta
How are most anesthetic drugs transferred?
Passive Transfer
Rate of blood flow impacts amount of drug crossing placenta
What can cause a drug to be trapped in placental tissue?
- High Lipid Solubility of a drug means more bilayer penetration
Example: Sufentanil
Name two local anesthetics that are highly protein-bound and less likely to cross the placenta.
- Bupivacaine
- Ropivacaine
Albumin binds to _________ and lipophilic compounds.
Acidic
Alpha-1-acid glycoprotein binds to _______ compounds.
Basic
What is pKa?
The pH at which 50% of the drug is ionized, and 50% of the drug is non-ionized
Which drug (Non-ionized or Ionized) tends to cross the placenta more easily?
Non-ionized cross the placenta more easily
How does ion trapping occur in the fetus?
- The fetus usually has a lower pH than the mother d/t increase metabolism
- Hydrogen ions bind to non-ionize form of the drug and trap it in fetal circulation
What are examples of drugs that are non-ionized and can cross the placenta.
- Local anesthetic
- Opioids
Does succinylcholine cross the placenta?
- No
- SCh is highly ionized and does not cross the placenta
Most drugs with a molecular weight less than _______ cross the placenta.
Less than 500 Daltons
Most drugs with a molecular weight greater than _______ do not cross the placenta.
Greater than 1000 Daltons
What are examples of large molecular weight drugs that do not cross the placenta?
- Non-depolarizing Muscle Relaxers
- Heparin
- Protamine
Drugs that can readily cross the placenta (Long List)
- Anticholinergics (Atropine, Scopolamine)
- Anti-hypertensives (β-antagonist, NitroP, NTG)
- Anti-cholinesterase (Neostigmine)
- Anti-coagulants (Warfarin)
- Acetaminophen
- BZD
- Induction agents (Prop, Ketamine, Etomidate, Precedex)
- VA
- LA (Lidocaine)
- Opioids
- Ephedrine
Drugs that DO NOT readily cross the placenta
- Anticholinergics (Glycopyrrolate)
- Anti-coagulant (Heparins)
- Muscle Relaxants (SCh and Non-depolarizers)
- Sugammadex
- Phenylephrine
