Advanced Principles A > OB 2 > Flashcards

OB 2 Flashcards

Exam 2 (90 cards)

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1
Q

Concept: P50

A

Definition: The oxygen level at which hemoglobin is 50% saturated.

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2
Q

What is the approximate uterine blood flow at term in ml/min?

A

~700 ml/min

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3
Q

At term, uterine blood flow represents approximately what percentage of total maternal cardiac output?

A

12%

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4
Q

Why is the uterine arterial bed considered to have low resistance at term?

A

It is maximally dilated to accommodate high blood flow.

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5
Q

What are the primary anatomical sources of uterine blood flow?

A

The uterine arteries.

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6
Q

The uterine arteries are branches of which maternal vessels?

A

The internal iliac (hypogastric) arteries.

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7
Q

What are the secondary anatomical sources of uterine blood flow?

A

The ovarian arteries.

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8
Q

From which vessel and at what vertebral level do the ovarian arteries branch?

A

The aorta at the L4 level.

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9
Q

What percentage of uterine blood flow passes through the intervillous space?

A

70%-90% - low resistance system for exchange of gas and nutrients

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10
Q

What is the formula for Uterine Blood Flow?

A

Uterine perfusion pressure/uterine vascular resistance

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11
Q

How is Uterine Perfusion Pressure calculated?

A

Uterine arterial pressure - Uterine venous pressure.

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12
Q

What unique characteristic describes UBF regulation regarding maternal blood pressure?

A

There is no autoregulation of UBF in pregnancy.

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13
Q

What is the primary maternal factor that Uterine Blood Flow is dependent upon?

A

Maternal blood pressure.

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14
Q

List the three broad categories of physiological changes that decrease Uterine Blood Flow.

A

Decreased uterine arterial pressure, increased uterine venous pressure, and increased uterine vascular resistance.

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15
Q

How does the supine position decrease uterine arterial pressure?

A

Via aortocaval compression.

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16
Q

Besides aortocaval compression, list two causes of hypovolemia that decrease uterine arterial pressure.

A

Dehydration and bleeding (hemorrhage).

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17
Q

How does neuraxial anesthesia lead to decreased uterine arterial pressure?

A

By causing a sympathetic blockade resulting in hypotension.

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18
Q

List the drug classes or specific agents that can decrease uterine arterial pressure through drug-induced hypotension.

A

Propofol, volatile agents, magnesium, and opioids

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19
Q

What are the two primary recommended treatments for maternal hypotension to maintain UBF?

A

Fluid bolus and vasoconstrictors.

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20
Q

How does the supine position specifically increase uterine venous pressure?

A

Via inferior vena cava (IVC) compression.

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21
Q

What is the relationship between uterine contraction strength and UBF?

A

Uterine blood flow is inversely related to contraction strength.

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22
Q

What term describes a state of excessive uterine contractions that increases venous pressure?

A

Tachysystole - hyperemia during uterine relaxation

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23
Q

List two exogenous substances that can induce drug-induced tachysystole.

A

Oxytocin and cocaine (or methamphetamine).

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24
Q

Identify two maternal activities or conditions, other than contractions, that increase uterine venous pressure.

A

Pushing effort and seizures.

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25
How does maternal stress or hypotension increase uterine vascular resistance?
By stimulating the release of endogenous catecholamines.
26
Which two exogenous catecholamines are commonly used to treat maternal hypotension?
Phenylephrine and Ephedrine.
27
Why might Ephedrine be less desirable than Phenylephrine for treating hypotension in the fetus?
It crosses the placenta and increases fetal metabolic requirements, potentially decreasing fetal pH, base excess, and umbilical oxygen content
28
Which vasopressor is often considered the 'choice' for maternal hypotension, especially if repeated doses are needed?
Phenylephrine
29
What is the effect on UBF when a 10-15 mcg Epinephrine epidural test dose is given to a healthy parturient?
There is no change in UBF.
30
What is the effect on UBF when Epinephrine is administered intravenously?
Uterine blood flow decreases.
31
What is the effect of epidural Clonidine or Dexmedetomidine on UBF?
There is no change in UBF.
32
By what mechanism do intravenous Clonidine and Dexmedetomidine decrease UBF?
By decreasing uterine arterial pressure (hypotension).
33
How does neuraxial anesthesia improve UBF in a patient experiencing significant pain?
By providing pain control and decreasing circulating catecholamines.
34
Under what condition does neuraxial anesthesia cause a decrease in UBF?
When sympathectomy leads to uncorrected maternal hypotension.
35
What are the two primary mechanisms by which Magnesium Sulfate increases UBF?
Smooth muscle relaxation and vasodilation leading to decreased UVR
36
By what specific mechanism does Hydralazine increase Uterine Blood Flow?
Direct relaxation of arterioles, which decreases uterine vascular resistance.
37
What is the effect of volatile anesthetic agents on UBF when administered at 0.5-1.5 MAC?
There is a minimal effect on UBF.
38
Why does a high MAC of volatile agents lead to decreased UBF?
It decreases maternal cardiac output and blood pressure, reducing uterine arterial pressure.
39
Concept: Chorionic Plate
Definition: The fetal side of the placenta.
40
Concept: Basal Plate
Definition: The maternal side of the placenta.
41
How much maternal blood is typically accommodated in the intervillous space?
~350 ml
42
Through which vessels does maternal blood enter the intervillous space?
Spiral arteries
43
Transfer of substances within the intervillous space depends on which 3 factors?
1. Concentration gradient 2. Permeability 3. Restriction of movement
44
What are the 4 transfer mechanisms of placental transfer?
Passive, active, facilitated, and pinocytosis
45
Placental transfer: How does facilitated diffusion differ from simple diffusion?
It utilizes carrier proteins but still moves down a concentration gradient.
46
What occurs to the rate of facilitated diffusion when all binding sites are occupied?
The rate of transfer is 'maxed out' due to saturation kinetics.
47
What is an example of placental facilitated diffusion?
glucose
48
How does temperature influence facilitated diffusion?
higher temp = increased transfer
49
Placental transfer: What are the two requirements for active transport?
Energy (ATP) and a protein membrane carrier.
50
List three electrolytes transferred across the placenta via active transport.
Sodium, Potassium, and Calcium.
51
Concept: Pinocytosis
Definition: The transfer of large macromolecules via membrane rearrangement and vesicle formation.
52
Which specific immune molecule is transferred from mother to fetus via pinocytosis?
Immunoglobulin G (IgG).
53
What are the 5 pharmacokinetic factors that impact drug transfer across the placenta?
Blood flow, lipid solubility, protein binding, pKa (pH/charge), and molecular size.
54
How does lipid solubility impact placental drug transfer? Give an example
highly lipid soluble drugs = bilayer penetration - may encourage drug to become trapped in placental tissue - sufentanil
55
Which maternal protein typically binds to acidic and lipophilic drug compounds?
Albumin
56
Which maternal protein typically binds to basic drug compounds?
Alpha1-Acid Glycoprotein
57
Why are Bupivacaine and Ropivacaine less likely to cross the placenta than other local anesthetics?
They are highly protein bound.
58
Between ionized and non-ionized drugs, which crosses the placenta more easily?
Non-ionized drugs.
59
Describe the mechanism of 'ion trapping' in the fetus.
Basic drugs cross the placenta non-ionized, enter the more acidic fetal environment, become ionized, and can no longer cross back.
60
Which drugs are susceptible to ion trapping?
LAs and opioids
61
Why does Succinylcholine not cross the placenta easily?
It is highly ionized.
62
Most drugs with a molecular weight greater than _____ Daltons do not cross the placenta.
1000 Da
63
Drugs with molecular weight less than _____ can cross the placenta
500 Da
64
List three examples of drugs with high molecular weights that do not cross the placenta.
Non-depolarizing muscle relaxers, Heparin, and Protamine.
65
Which anticholinergic agents cross the placenta?
Atropine and scopolamine
66
Which anticholinergic agent does NOT cross the placenta?
Glycopyrrolate
67
Why is Atropine preferred over Glycopyrrolate when reversing neuromuscular blockade in a pregnant patient?
To counteract fetal bradycardia caused by the crossing of neostigmine.
68
Which antihypertensive agents cross the placenta readily?
Beta antagonists, nitroprusside, NTG
69
Which anticholinesterases cross the placenta easily?
Neostigmine and edrophonium
70
Which anticoagulant crosses the placenta and is therefore avoided?
Warfarin
71
Which induction agents are known to cross the placenta?
Propofol, Ketamine, and Etomidate.
72
Which anticoagulant does NOT cross the placenta readily?
Heparin
73
What is the status of Sugammadex use in the pregnant population?
It has not been studied widely and is not recommended.
74
What is the critical gestational age range for teratogenic drug effects?
15 to approximately 60 days.
75
Although nitrous oxide has theoretical concerns regarding DNA synthesis, what have human studies concluded about its teratogenicity?
It has not been found to be associated with congenital abnormalities in humans.
76
How does the FDA assign safety categories to medications for pregnant patients?
PLLR - pregnancy and lactation labeling role
77
Chronic exposure to which drug class is associated with cleft palate formation in the first 6 weeks of pregnancy?
Benzodiazepines (e.g., Diazepam).
78
What is the FDA teratogenicity rating for Diazepam?
Class D - positive evidence of risk; only chronic use within the 1st 6 weeks
79
How does morphine affect the fetus?
Dec maternal RR - deoxygenation in fetus - fewer fetal HR accelerations
80
Why is Remifentanil considered to have minimal fetal exposure despite maternal use?
It undergoes rapid metabolism - can cause resp depression if given close to delivery
81
How does butophanol (Stadol) impact the fetus?
good pain relief for mom w/o s/e to fetus
82
What is the primary factor limiting oxygen transfer across a normal, healthy placenta?
Blood flow to the placenta (maternal UBF).
83
How does the P50 of fetal hemoglobin (HbF) compare to adult hemoglobin (HbA)?
Fetal hemoglobin has a lower P50 - shift to left
84
What is the physiological advantage of the lower P50 found in fetal hemoglobin?
It has a higher affinity for oxygen, allowing it to 'pull' oxygen from maternal blood effectively.
85
Concept: Bohr Effect
Definition: The shift in hemoglobin's oxygen affinity caused by changes in carbon dioxide concentration and pH
86
In the Double Bohr effect, what happens to the maternal oxyhemoglobin dissociation curve as fetal CO2 enters maternal blood?
It shifts to the right, enhancing the release of oxygen.
87
In the Double Bohr effect, why does the fetal oxyhemoglobin dissociation curve shift to the left?
Fetal blood loses CO2 to the mother, becoming more alkaline and increasing its oxygen affinity.
88
How does maternal hyperventilation/ alkalosis impair fetal oxygenation?
It shifts the maternal oxyhemoglobin curve to the left, making the mother 'hold onto' oxygen more tightly.
89
Severe fetal hypercapnia can lead to which two dangerous fetal conditions?
Fetal acidosis and myocardial depression.
90
What are the P50 values of adult and fetal Hb?
Adult - 27 mmHg Fetal - 19 mmHg
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