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S5 - Regional/OB - Test 1 > Uterine Blood Flow & Placental Transfer > Flashcards

Uterine Blood Flow & Placental Transfer Flashcards

1
Q

Main blood supply to uterus

A

Uterine arteries

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2
Q

Secondary source of blood supply to uterus (lesser, variable contribution)

A

Ovarian arteries

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3
Q

what supplies oxygenated blood to the intervillous space?

A

spiral arteries

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4
Q

where does maternal and fetal gas, nutrient, and waste exchange occur?

A

the intervillous space

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5
Q

How does deoxygenated blood return to maternal circulation?

A

Through uterine and ovarian veins

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6
Q

What mechanism allows increased uterine blood flow to meet needs of the growing uterus and fetus?

A

Uterine arteries are maximally dilated allowing more flow

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7
Q

What supplies blood to the placenta?

A

maternal arcuate, radial and spiral arteries?

or maybe the intervillous space?

who fcking knows but it aint me and it aint MBG

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8
Q

What happens to pressure as it goes towards the intervillous space?

A

Decreases

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9
Q

Which do you expect to have the highest pressure?

Spiral arteries?
Intervillous space?
Uterine arteries?
Radial arteries?

Lowest?

A

Uterine arteries- highest

Intervillous space- lowest

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10
Q

Uterine blood flow at term

A

800 ml/min

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11
Q

Blood flow to myometrium

A

150 ml/min

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12
Q

Blood flow to decidua (placenta)

A

100 ml/min

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13
Q

What percent of cardiac output is directed towards the uterus?

A

10-20%

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14
Q

When do vascular changes occur in pregnancy?

A

FIrst 3 months

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15
Q

What happens to vessel and diameter lenghth pregnancy?

A

Both increase, but diameter more so than length

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16
Q

What can decrease uterine blood flow?

A
  1. Contractions
  2. Hypertension
  3. Hypotension
  4. Exogenous vasoconstrictors
  5. Local anesthetic toxicity
  6. Increased uterine tone associated with sympathetic block
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17
Q

What are the two mechanisms by which uterine blood flow is decreased?

A

Decreased perfusion pressure
Increased uterine vascular resistance

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18
Q

What are the two mechanisms by which perfusion pressure is decreased to uterus?

A

Decreased uterine arterial pressure
Increased uterine venous pressure

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19
Q

Causes of decreased uterine arterial pressure

A
  • Supine position (aortocaval compression)
  • Hemorrhage/hypovolemia
  • Drug induced hypotension
  • Hypotension during sympathetic block
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20
Q

Causes of increased uterine venous pressure

A
  • Venacaval compression
  • Uterine contraction
  • Drug induced tachysystole
  • Skeletal muscle hypertonus (seizures, valsalva)
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21
Q

Which endogenous vasoconstrictors cause increased uterine vascular resistance?
What causes these to be released?

A
  • Catecholamines (in response to stress)
  • Vasopressin (in response to hypovolemia)
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22
Q

Which exogenous vasoconstrictors cause increased uterine vascular resistance?

A
  • Epi
  • Vasopressors (phenylephrine > ephedrine)
  • Local anesthetics in high concentrations
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23
Q

How to determine uterine blood flow?

A

Uterine perfusion pressure / Uterine vascular resistance

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24
Q

How does neuraxial anesthesia cause increased uterine blood flow?

A
  • Pain relief
  • Decreased sympathetic activity
  • Decreased maternal hyperventilation
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25
Q

How does neuraxial anesthesia cause decreased uterine blood flow?

A
  • Hypotension
  • Unintentional IV injection of local anesthetic or epi
  • Absorbed local anesthetic (little effect)
26
Q

What effect do commonly used induction agents have on uteroplacental blood flow?

A

Little to no effect

27
Q

What effect do inhalational agents have on uterine blood flow?

A

Little to no effect

28
Q

Indirect effects of GA on uteroplacental blood flow

A
  • Blood pressure changes
  • Sympathetic response (laryngoscopy/intubation
29
Q

What changes in hemodynamics are associated with deeper planes of anesthesia that may effect uterine blood flow?

A

Negatives: reduction in CO, maternal BP, and uterine artery blood flow

Positives: vasodilation

30
Q

What occurs as a result of dose dependent reduction in uterine tone associated with inhalational agents?

A

Increased blood flow

31
Q

Which inhalational agent is BEST for a lil mama based on blood flow?

A

Trick question…
No reason to choose one over another

32
Q

What carries oxygen poor blood from the fetus to the placenta?

A

Umbilical arteries (2)

33
Q

How does blood enter fetal circulation?

A

Through the ductus venosus

34
Q

What carries oxygen rich blood from the placenta to the fetus?

A

Umbilical vein (1)

35
Q

At what maternal SBP does inadequate fetal oxygenation occur in awake healthy patients during labor epidural analgesia?

A

<100 mm Hg

36
Q

Label 1-5

A
  1. Umbillical arteries (2)
  2. Umbilical vein (1)
  3. Fetal capillaries
  4. Intervillous space
  5. Spiral arteries
37
Q

Flow may differ between the R and L uterine arteries, whcih USUALLY gets more?

A

The side the placenta is implanted on

38
Q

What four things affect placental transfer of drugs?

A
  1. Concentration
  2. Molecular weight
  3. Lipid solubility
  4. Ionization
39
Q

Which drug will cross placenta more readily?

Smaller molecular weight (<500 Da) or Larger MW (>100 Da)?

More lipid or water soluble?

Ionized or unionized?

A

Smaller

More lipid soluble

More unionized

40
Q

How are drugs diluted as they get closer to the baby?

A

Diluted in maternal blood

Diluted in intervillous blood

Diluted in Placental blood

Circulate to fetus then diluted in fetal blood

Then first pass effect through liver

41
Q

How does blood bypass the fetal liver?

A

Ductus venosus

42
Q

What percent of fetal CO returns to the placenta without circulating?

A

20 percent

43
Q

Does all umbilical venous blood bypass the liver via the ductus venosus?

A

No

44
Q

Can the fetus and neonate metabolize drugs at all?

A

Yes, but at a much slower rate than adults

45
Q

When the fetus excretes drugs into the urine what happens to them?

How are they actually eliminated?

A

Excreted and later swallowed as amniotic fluid

Actual elimination is mostly dependent on placental transfer

46
Q

How does maternal FRC and MV differ from norm?

Effect on uptake and absorption of inhaled agents?

A

Reduced FRC

Increased MV

Increased (more rapid) uptake of inhaled agents

47
Q

What effect does increased CO have on distribution to tissues?

A

Increased distribution to all tissues

48
Q

How much does total body water increase on average?

What is the significance of this?

A

Increases on average 8L

Increased Vd for hydrophilic drugs

49
Q

How much is hepatic blood flow increased?

A

Ha… gotcha…. It is not significantly increased

50
Q

Maternal changes in CYP enzymes

A

Some have increased activity

some have decreased activity

………….

51
Q

Maternal effect on renal blood flow and GFR

Significance?

A

Increased

Drgus that are excreted by kidneys unchanged (like cephalosporins) are eliminated faster

52
Q

How can drugs be transferred across the placenta?

A
  • Simple diffusion
  • Simple diffusion via channels
  • Facilitated diffusion
  • Active transport
  • Endocytosis
53
Q

Which anticholinergics readily cross the placenta?

Atropine, Scopolamine, Glycopyrrolate

A

Atropine and scopolamine

54
Q

Which commonly given drugs in anesthesia make for a floppy baby if given before cord is cut because they readily cross placenta?

A

Opioids and benzos (Diazepam and midazolam)

55
Q

Which vasopressor readily crosses placenta?

Phenylephrine or ephedrine?

A

ephedrine

56
Q

Do induction agents and inhalation agents readily cross the placenta?

A

Yes

Propofol, ketamine, etomidate, thiopental

All the volatiles and nitrous

57
Q

Do local anesthetics readily cross the placenta?

A

Yes

Except chlorprocaine

58
Q

Do muscle relaxants readily cross the placenta?

A

Nope

59
Q

Does heparin readily cross placenta?

A

Nope

60
Q

Do antihypertensives readily cross placenta?

A

Yes

Beta blockers

Nipride

Nitroglycerine

61
Q
A
62
Q

what is primarily responsible for supplying oxygenated maternal blood to the uterus?

(quiz question)

A

uterine arteries

S5 - Regional/OB - Test 1 (13 decks)

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