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 resistance
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.
UBF exceeds the minimal demand for fetal oxygen - gives a little leeway
17
Q
What are the 3 big 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
around 13-16 weeks gestation
19
Q
Hypovolemia will result in decreased _________ and thus decreased UBF.
A
decreased uterine arterial pressure
dehydration, bleeding
20
Q
How will neuraxial anesthesia affect UBF?
A
Sympathetic blockade → hypotension → decreased uterine arterial pressure = ↓ UBF
21
Q
What 2 other thing can cause HoTN and decreased arterial pressure/UBF?
A
- Hemorrhage
- Drugs (Prop, VA, Mg, Opioids) dose-dependent
22
Q
What should be administered prior to epidural placement?
A
Fluid bolus to counteract hypotension.
23
Q
How will supine positioning affect uterine venous pressure?
A
↑ venous pressure due to IVC compression
24
Q
How will contractions effect uterine venous pressure?
A
- Contractions = ↑ venous pressure
- Tachysystole (Lots of strong contractions in short term.)
25
What drugs will cause a tachysystolic state?
- **Oxytocin**
- Cocaine/Meth
26
What occurs with uterine blood flow during uterine relaxation? (such as after a contraction)
Hyperemia (increased blood flow)
## Footnote
**uterus like a sponge squeezing blood out**
27
What factors will increase uterine vascular resistance?
- Endogenous vasocontrictors (catecholamines from stress response)
- Exogenous catecholamines (Phenylephrine & Ephedrine)
28
Is phenylephrine or ephedrine preferred for parturient patients?
Phenylephrine
Ephredrine can be used but crosses placental barrier and increases fetal metabolic requirements.
29
How does epinephrine, administered neuraxially, affect UBF?
- No change in healthy patients
30
What test dose of epinephrine is used in neuraxial anesthesia for parturient patients?
10 - 15 mcg
## Footnote
**no change in UBF**
31
Does Epinephrine IV affect UBF?
Yes - decreases UBF (dose-dependent) d/t **increased UVR**
32
How do clonidine and precedex affect UBF when administered:
Neuraxially?
Intravenously?
- Neuraxial = No change in UBF
- IV = ↓ UBF
33
Neuraxial anesthesia will increase UBF if _________ is avoided.
hypotension from sympathectomy
* decreased circulating catecholamines
* pain control
34
How does Magnesium Sulfate affect UBF?
* Dose-dependent **increase in UBF**
* relaxes smooth muscle = decreased UVR
35
What happens to UBF if too much Mg Sulfate is given?
* decreased UBF if the patient is getting so much that their BP drops
36
How does Hydralazine affect UBF?
**increases UBF** d/t decreased UVR & relaxation of arterioles
37
How do volatile anesthetics affect UBF?
↓ UBF if MAC > 1.5 (obviously rare) **decreased CO & BP = decreased UAP & UBF**
Minimal effect on UBF with MAC 0.5 - 1.5
38
The chorionic plate of the placenta faces the _____.
fetus
39
The basal plate of the placenta faces the _______.
mother
40
What is the **mainstem villus** in the placenta?
* comes off chorionic plate
* contains fetal capillaries
* **where gas exchange will occur b/w fetal capillaries & maternal blood that is in the intervillous space**
41
What are the **spiral arteries** in the placenta?
* on the maternal (basal) side
* where the maternal blood comes in & pools in the intervillous space
42
How many Umbilical Veins are there?
1
* it takes oxygenated blood to the fetus (blue on the image)
43
How many umbilical arteries are there?
2
* they take deoxygenated blood from the fetus back to the maternal circulation through the placenta
* (red in the image)
44
What are the functions of the placenta?
- Production of proteins, hormones, enzymes
- Gas exchange
- Nutrient & waste exchange
45
What is the intervillous space?
Large placental sinus with multiple folds
46
The intervillous space is a high resistance area. T/F?
False. The intervillous space is a low resistance area (for gas exchange)
47
How much blood is in the intervillous space at one time?
350mls
## Footnote
* 70-90% of blood flow through the uterus is going through & pools here
48
Where does blood enter into the intervillous space from?
spiral arteries
49
The umbilical vein carries __________ blood.
oxygenated
50
The umbilical arteries (two in number) carry ________ blood.
deoxygenated
51
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 within the placental tissue or to proteins to prevent fetal uptake)
52
What concentration gradient does **O2** move down in maternal-fetal gas exchange?
* from the pool of maternal blood into the intervillous space
* then to fetal capillaries
53
What concentration gradient does **CO2** move down in maternal-fetal gas exchange?
* from fetal circulation into maternal blood
54
What substances/drugs move via passive diffusion?
**movement along a concentration gradient**
- - O₂
- CO₂
- Most anesthetic drugs
55
What is facilitated diffusion?
**movement w/ the help of carrier proteins - still follows concentration gradient**
Ex: Glucose
56
When talking about facilitated diffusion, what is **saturation kinetics**?
When all available binding sites are saturated = rate of transfer maxed out
**only able to transfer so much until carrier proteins are saturated**
57
In regards to facilitated diffusion, a higher temperature will ______ rate of diffusion.
increase
58
What's an example of a molecule that moves via facilitated diffusion?
Glucose
59
Active transport requires ____.
Active transport also involves ________ ________ and ________ inhibition.
**movement against the concentration gradient**
- requires ATP (protein membrane carrier)
- Saturation kinetics
- Competitive inhibition
ex. Na⁺, K⁺, Ca⁺⁺
60
What transfer mechanism is characterized by cellular engulfment, membrane rearrangement, vesicle formation, and the movement of large macromolecules?
Pinocytosis
## Footnote
**requires energy**
61
What is an example of pinocytosis transfer in pregnancy?
Transfer of IgG from mother to fetus
62
What are the major factors that impact drug transfer across the placenta? **5**
- **Blood flow**
- Lipid solubility
- Protein binding
- pKa & pH/charge
- Molecular size
(Also, gestational age, maternal factors, and placental drug metabolism).
63
What is the primary factor affecting anesthetic drug delivery across the placenta? Why?
Blood flow because most drugs are passively transferred.
## Footnote
**from high concentration to low**
64
High lipid solubility results in _______ bilayer penetration.
more
## Footnote
**may encourage drug to be trapped in placental tissue (ion trapping)**
65
What drug is an example of high lipid solubility resulting in placental tissue trapping of the drug?
Sufentanil
66
Why are bupivacaine and ropivacaine less likely to cross the placenta?
Both are **highly protein-bound**.
67
Albumin binds to _____ and ________ compounds.
acidic & lipophillic
68
α-1 acid glycoprotein binds to ______ compounds.
basic
69
What is pKa?
The pH at which 50% of a drug is ionized & 50% is non-ionized
70
Do ionized or non-ionized drugs tend to cross the placenta more easily?
non-ionized
71
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.
72
What are examples of highly ionized drugs that don't cross the placenta easily?
- Succinylcholine
73
What are examples of drugs that are non-ionized and subject to ion trapping?
* Lidocaine
* Opioids
74
Drugs with a molecular weight of ________ typically cross the placenta.
< 500 Da (Daltons)
75
Most drugs with a molecular weight of _______ do not cross the placenta.
> 1000 Da (Daltons)
76
What are examples of drugs that don't cross the placenta due to their high molecular weight?
- ND NMBD's
- Heparin
- Protamine
77
What anticholinergics readily cross the placenta?
- **Atropine**
- Scopolamine
78
What anti-hypertensives readily cross the placenta?
- β blockers
- Nitroprusside
- Nitroglycerin
79
What local anesthetic can readily cross the placenta? (in contrast to other LA's)
Lidocaine
80
What drug classes typically are able to readily cross the placenta?
- Anticholinergics
- Anti-hypertensives
- VAA's
- Benzo's
- Ephedrine
- Induction agents (prop, ketamine, etomidate, dex)
- Tylenol
- **Neostigmine**
- Warfarin
81
What drugs **DO NOT** readily cross the placenta?
- **Glycopyrrolate**
- Heparin
- Succinylcholine
- NDNMBD's
- Sugammadex*
- Phenylephrine
82
What drugs should be used to reverse paralysis in pregnant patients? Why?
**Neostigmine & Atropine**
Glyco does not cross the placenta - the fetus will have bradycardia with neostigmine
## Footnote
**atropine will prevent brady in mom & fetus**
83
T/F Sugammadex is safe in preganancy
False
* 1st trimester - can encapsulate pregnancy hormones
* not studied widely in pregnancy
84
What is a teratogen?
Substance that increases the risk of a fetal defect
* must be given in a sufficient dose & at a critical point in development to cause defect
85
When during development are teratogens most likely to cause fetal defect?
15 - 60 days gestational age
86
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.
87
What drug that we commonly use is not regulated by the FDA?
N₂O (medical gas, not drug)
88
What is the teratogenicity profile of benzodiazepines?
- Probable cleft palate formation from GABA activity
- Chronic exposure (not a one time low dose)
*Especially Diazepam*.
89
How does meperidine effect the fetus?
- Neonate CNS depression
- Can cause seizures due to normeperidine accumulation
90
How does morphine affect the fetus?
- ↓ maternal respirations = ↓ fetus O₂
- fewer fetal heart rate accelerations
91
What opioid can be really useful for maternal sedation? Why?
Remifentanil
*Rapid metabolism = minimal fetal exposure*.
92
What mixed opioid agonsist-antagonist is commonly given in L&D for pain control?
Butorphanol (stadol)
* less fetal side effects.
93
What is P50 ?
The partial pressure of O₂ at which Hgb is 50% saturated with O₂
94
At ____ mmHg of partial pressure of oxygen, 50% of fetal hgb are saturated.
19mmHg
95
What is the P50 of adult Hgb?
27 mmHg PO2
96
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.
97
A lower P50 will result in a ________ affinity for oxygen.
higher
98
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
99
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*
100
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*
101
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
102
How will maternal **hypoventilation & hypercapnia** affect the fetus?
CO2 crosses the placenta = fetal acidosis & fetal myocardial depression
