Uteroplacental & Fetal Physiology Pt. 1 (Exam 2) Flashcards
What does UBF stand for?
Uterine Blood Flow
What does IUGR stand for?
Intrauterine Growth Restriction
What does PIH stand for?
Pregnancy Induced Hypertension
What does Gravida mean?
number of pregnancies
What does Para mean?
number of live births or >20 weeks
What does P50 mean?
Oxygen partial pressure level at which Hgb is 50% saturated
What does HbF stand for? HbA?
HbF = Fetal Hemoglobin
HbA = Adult Hgb
Uterine perfusion increases or decreases throughout gestation?
Increases
What is uterine blood flow at term?
What percentage of maternal CO is this?
- ~700 ml/min
- ~12% of CO
Pregnancy is ____ resistance, but _____ flow.
Low Resistance, High Flow
Systemic Vasodilation w/ ↑ volume & CO
What is the primary source of uterine blood flow?
Uterine Arteries that branch from internal iliac (hypogastric) arteries
What is the secondary source of uterine blood flow?
Ovarian Arteries that branch from the aorta at the L4 level
70 - 90% of uterine blood flow will pass through the ________ space.
Intervillous space
Low resistance area of maternal blood pooling for exchange of gas nutrients.
Uterine blood flow = [__________] ?
Formula for uterine blood flow.
Uterine perfusion pressure ÷ Uterine vascular pressure
Uterine perfusion pressure = [__________]?
Uterine arterial pressure - uterine venous pressure
What is the mechanism for autoregulation of UBF during pregnancy?
There is no autoregulation of UBF. Entirely dependent on maternal blood pressure.
this is why UBF exceeds minimal demand for fetal oxygen (cushion)
What are the overarching causes of decreased UBF?
- ↓ uterine arterial pressure
- ↑ uterine venous pressure
- ↑ uterine vascular resistance
What position would compromise uterine arterial pressure?
Supine position due to aortocaval compression
Hypovolemia will result in decreased _________ and thus decreased UBF.
decreased uterine arterial pressure
potentially from hypovolemia or bleeding
How will neuraxial anesthesia affect UBF?
Sympathetic blockade → hypotension → decreased uterine arterial pressure = ↓ UBF
What should be administered prior to epidural placement?
Fluid bolus to counteract hypotension.
typically recommended to co-load, instead of prior administration
How will supine positioning affect uterine venous pressure?
↑ venous pressure due to IVC compression ⇒ ↓UBF
What is tachysystole?
Condition of the uterus contracting too forcefully or too frequently (usually 5+ contractions in 10min or contraction lasting longer than 60seconds)
How will contractions effect uterine venous pressure?
- Contractions = ↑ venous pressure
- Tachysystole (Lots of strong contractions in short term.)
What drugs can cause a tachysystolic state?
- Oxytocin
- Cocaine/Meth
What occurs with uterine blood flow during uterine relaxation? (such as after a contraction)
Hyperemia (increased blood flow)
What factors will increase uterine vascular resistance?
- Endogenous vasocontrictors (catecholamines from stress response)
- Exogenous catecholamines (Phenylephrine & Ephedrine)
Is phenylephrine or ephedrine preferred for parturient patients?
- Phenylephrine
- Both are effective but Ephredrine crosses the placental barrier and increases fetal metabolic requirements. Has also been shown to decrease fetal pH, base excess, and umbilical O2 content.
High concentrations of local anesthetics will have what effect on uterine blood flow?
↓ UBF from high LA’s from:
- Arterial constriction
- Inhibition of endothelial vasodilation
- Stimulation of myometrial contraction
How does epinephrine (epi wash), administered neuraxially, affect UBF?
- No change in healthy patients
What test dose of epinephrine is used in neuraxial anesthesia for parturient patients?
10 - 15 mcg
(generally doesn’t change UBF)
How do clonidine and precedex affect UBF when administered:
Neuraxially?
Intravenously?
- Neuraxial = No change in UBF
- IV = ↓ UBF
Neuraxial anesthesia will increase UBF if _________ is avoided.
hypotension
(if HoTN is present, will lead to decreased UBF)
How does magnesium sulfate affect UBF?
- Relaxes smooth muscle, and causes vasodilation which increases UBF
- If HoTN is present, will lead to decreased UBF
How do volatile anesthetics affect UBF?
- ↓ UBF if MAC > 1.5
- Minimal effect on UBF with MAC 0.5 - 1.5
The chorionic plate of the placenta faces the _____.
fetus
The basal plate of the placenta faces the _______.
mother
What are the functions of the placenta?
- Production of proteins, hormones, enzymes
- Gas exchange
- Nutrient & waste exchange
What is the intervillous space?
Large placental sinus with multiple folds
The intervillous space is a high resistance area. T/F?
False. The intervillous space is a low resistance area.
How much blood is in the intervillous space at one time?
~350mls of maternal blood
Where does blood enter into the intervillous space from?
spiral arteries
The umbilical vein carries __________ blood.
oxygenated
The umbilical arteries (two in number) carry ________ blood.
deoxygenated
