Uteroplacental & Fetal Physiology Pt. 1 (Exam II) Flashcards
1
Q
What does UBF stand for?
A
Uterine Blood Flow
2
Q
What does IUGR stand for?
A
Intrauterine Growth Restriction
3
Q
What does PIH stand for?
A
Pregnancy Induced Hypertension
4
Q
What does Gravida mean?
A
of pregnancies
5
Q
What does Para mean?
A
of live births or >20 weeks
6
Q
What does P50 mean?
A
Oxygen level at which Hgb is 50% saturated
7
Q
What does HbF stand for?
A
Fetal Hemoglobin
HbA = Adult Hgb
8
Q
Uterine perfusion increases or decreases throughout gestation?
A
Increases
9
Q
What is uterine blood flow at term?
What percentage of CO is this?
A
~ 700 ml/min
~ 12% of CO
10
Q
Pregnancy is ____ resistance, but _____ flow.
A
Low Resistance, High Flow
Vasodilation w/ ↑ volume & CO
11
Q
What is the primary source of uterine blood flow?
A
Uterine Arteries that branch from internal iliac (hypogastric) arteries
12
Q
What is the secondary source of uterine blood flow?
A
Ovarian Arteries that branch from the aorta at the L4 level
13
Q
70 - 90% of uterine blood flow will pass through the ________ space.
A
Intervillous space
Low resistance area of maternal blood pooling for exchange of gas/nutrients.
14
Q
Uterine blood flow = __________ ?
Formula for uterine blood flow.
A
Uterine perfusion pressure ÷ Uterine vascular pressure
15
Q
Uterine perfusion pressure = __________?
A
Uterine arterial pressure - uterine venous pressure
16
Q
What is the mechanism for autoregulation of UBF during pregnancy?
A
Trick question. There is no autoregulation of UBF. Entirely dependent on maternal blood pressure.
17
Q
What are the overarching causes of decreased UBF?
A
- ↓ uterine arterial pressure
- ↑ uterine venous pressure
- ↑ uterine vascular resistance
18
Q
What position would compromise uterine arterial pressure?
A
Supine due to aortocaval compression
19
Q
Hypovolemia will result in decreased _________ and thus decreased UBF.
A
decreased uterine arterial pressure
20
Q
How will neuraxial anesthesia affect UBF?
A
Sympathetic blockade → hypotension → decreased uterine arterial pressure = ↓ UBF
21
Q
What should be administered prior to epidural placement?
A
Fluid bolus to counteract hypotension.
22
Q
Examples of drugs that can lead to decreased UAP:
A
- Propofol
- Volatiles
- Magnesium
- Opioids
*Dose Dependent
23
Q
How will supine positioning affect uterine venous pressure?
A
↑ venous pressure due to IVC compression
24
Q
Stronger Contractions = ___ UBF
A
Stronger Contractions = Slower UBF
25
How will contractions effect uterine venous pressure?
- Contractions = ↑ venous pressure
- Tachysystole (Lots of strong contractions in short term.)
26
What drugs will cause a tachysystolic state?
- **Oxytocin**
- Cocaine/Meth
27
What occurs with uterine blood flow during uterine relaxation? (such as after a contraction)
Hyperemia (increased blood flow)
28
What factors will increase uterine vascular resistance?
- Endogenous vasocontrictors (catecholamines from stress response)
- Exogenous catecholamines (Phenylephrine & Ephedrine)
29
Is phenylephrine or ephedrine preferred for parturient patients?
Phenylephrine
Ephredrine can be used but crosses placental barrier and increases fetal metabolic requirements.
30
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
31
How does epinephrine, administered neuraxially, affect UBF?
- No change in healthy patients
32
What test dose of epinephrine is used in neuraxial anesthesia for parturient patients?
10 - 15 mcg
33
How do clonidine and precedex affect UBF when administered:
Neuraxially?
Intravenously?
- Neuraxial = No change in UBF
- IV = ↓ UBF through increased UVR
34
Neuraxial anesthesia will increase UBF if _________ is avoided.
hypotension
35
How do volatile anesthetics affect UBF?
↓ UBF if MAC > 1.5 (obviously rare)
Minimal effect on UBF with MAC 0.5 - 1.5
36
The chorionic plate of the placenta faces the _____.
fetus
37
The basal plate of the placenta faces the _______.
mother
38
What are the functions of the placenta?
- Production of proteins, hormones, enzymes
- Gas exchange
- Nutrient & waste exchange
39
What is the intervillous space?
Large placental sinus with multiple folds
40
The intervillous space is a high resistance area. T/F?
False. The intervillous space is a low resistance area.
41
How much blood is in the intervillous space at one time?
350mls
42
Where does blood enter into the intervillous space from?
spiral arteries
43
The umbilical vein carries __________ blood.
oxygenated
44
The umbilical arteries (two in number) carry ________ blood.
deoxygenated
45
What variables change the rate and amount of transfer of (drugs, toxins, O₂, CO₂, etc.) in the intervillous space?
- Concentration gradient
- Permeability
- Restriction of movement (some substances are bound to in the placental tissue to prevent fetal uptake)
46
What substances/drugs move via passive diffusion?
- O₂
- CO₂
- Most anesthetic drugs
47
In regards to facilitated diffusion, a higher temperature will ______ rate of diffusion.
increase
48
What's an example of a molecule that moves via facilitated diffusion?
Glucose
49
Active transport requires ____.
What is required for active transport?
ATP
- Protein membrane carrier
- Saturation kinetics
- Competitive inhibition
ex. Na⁺, K⁺, Ca⁺⁺
50
What transfer mechanism is characterized by membrane rearrangement, vesicle formation, and the movement of large macromolecules?
Pinocytosis
51
What is an example of pinocytosis transfer in pregnancy?
Transfer of IgG from mother to fetus
52
What are the major factors that impact drug transfer across the placenta?
- **Blood flow**
- Lipid solubility
- Protein binding
- pKa & pH/charge
- Molecular size
(Also, gestational age, maternal factors, and placental drug metabolism).
53
What is the primary factor affecting anesthetic drug delivery across the placenta? Why?
Blood flow because most drugs are passively transferred.
54
High lipid solubility results in _______ bilayer penetration.
more
55
What drug is an example of high lipid solubility resulting in placental tissue trapping of the drug?
Sufentanil
56
Why are bupivacaine and ropivacaine less likely to cross the placenta?
Both are **highly protein-bound**.
57
Albumin binds to _____ and ________ compounds.
acidic & lipophillic
58
α-1 acid glycoprotein binds to ______ compounds.
basic
59
What is pKa?
The pH at which 50% of a drug is ionized & 50% is non-ionized
60
Do ionized or non-ionized drugs tend to cross the placenta more easily?
non-ionized
61
What is ion-trapping?
When the fetus has a lower pH than the mother resulting in drugs being trapped in fetal circulation via H⁺ binding to non-ionized drug.
62
Are the following drugs more or less subjected to ion trapping?
- LA’s
- Opioids
- Succinylcholine
- LA's: Non-ionized = therefore more subject to ion-trapping
- Opioids: Non-ionized = therefore more subject to ion-trapping
- Succinylcholine: Highly ionized = therefore less likely to cross the placental barrier
63
Drugs with a molecular weight of ________ typically cross the placenta.
< 500 Da (Daltons)
64
Most drugs with a molecular weight of _______ do not cross the placenta.
> 1000 Da (Daltons)
65
What are examples of drugs that don't cross the placenta due to their high molecular weight?
- ND NMBD's
- Heparin
- Protamine
66
What anticholinergics readily cross the placenta?
- **Atropine**
- Scopolamine
67
What anti-hypertensives readily cross the placenta?
- β blockers
- Nitroprusside
- Nitroglycerin
68
What local anesthetic can readily cross the placenta? (in contrast to other LA's)
Lidocaine
69
What drug classes typically are able to readily cross the placenta?
- Anticholinergics
- Anti-hypertensives
- VAA's
- Benzo's
- Ephedrine
- Induction agents
- Tylenol
- **Neostigmine**
- Warfarin
| BEAT WIN VA
70
What drugs **DO NOT** readily cross the placenta?
- **Glycopyrrolate**
- Heparin
- Succinylcholine
- NDNMBD's
- Sugammadex*
- Phenylephrine
71
What drugs should be used to reverse paralysis in pregnant patients? Why?
**Neostigmine & Atropine**
Glyco does not cross the placenta, thus neostigmine will cause severe fetal bradycardia in conjunction with neostigmine. Use atropine to avoid this.
72
What is a teratogen?
Substance that increases the risk of a fetal defect
73
When during development are teratogens most likely to cause fetal defect?
15 - 60 days gestational age
74
Which anesthetics drugs are proven teratogens?
**None**
However, we like to minimize or eliminate fetal exposure to anesthesia in the 15 - 60 days gestational period.
75
What drug that we commonly use is not regulated by the FDA?
N₂O (medical gas, not drug)
76
What is the teratogenicity profile of benzodiazepines?
- Probable cleft palate formation from GABA activity
- Chronic exposure (not a one time low dose)
*Especially Diazepam*.
77
How does meperidine effect the fetus?
- Neonate CNS depression
- Can cause seizures due to normeperidine accumulation
78
How does morphine affect the fetus?
- ↓ maternal respirations = ↓ fetus O₂
- fewer fetal heart rate accelerations
79
What opioid can be really useful for maternal sedation? Why?
Remifentanil
*Rapid metabolism = minimal fetal exposure*.
80
At ____ mmHg of partial pressure of oxygen, 50% of fetal hgb are saturated.
19mmHg
81
What is the P50 of adult Hgb?
27 mmHg PO2
82
How does the P50 of HbF compare to that of HbA?
HbF = 19 mmHg
HbA = 27 mmHg
HbF will preferentially pick up O₂ from the mother's blood.
83
A lower P50 will result in a ________ affinity.
higher
84
What concept is linked with the increase of CO₂ and decrease of pH resulting in a _______ affinity of Hgb for oxygen.
Bohr Effect
decreased affinity
85
The presence of CO₂ and blood acidity in fetal blood will _______ the release of of O₂ from maternal hemoglobin.
enhance
***R**ight shift = **R**elease*
86
What happens as the CO₂ content of fetal blood decreases?
Fetal blood becomes alkaline → curve shifts left → facilitates more O₂ uptake by HbF (increased affinity).
*Left shift = Lock*
87
How will maternal hyperventilation affect fetal oxygenation?
Hyperventilation = hypocapnia/maternal alkalosis → maternal oxyhemoglobin curve shifts left and prevents as much O₂ from getting to the baby
88
How does neuraxial anesthesia increase UBF?
- Decrease in circulating catecholamines
- Pain Control
89
What effect do Mg Sulfate and hydralazine have on both UBF and UVR?
BOTH increase UBF and Decrease UVR
90
What mixed agonist/antagonist drug is commonly used for pain relief in L&D?
Why?
Butorphanol (Stadol)
- Good pain relief without many side effects to the fetus
