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Methods of Anesthesia > Maternal & Fetal Physiology > Flashcards

Maternal & Fetal Physiology Flashcards

1
Q

Maternal/fetal blood flow steps (5)

A
  1. Blood comes from the mother’s uterine artery to the placenta
  2. From the placenta, oxygenated blood is delivered to the fetal R atrium via the umbilical vein
  3. From the fetal R atrium, blood goes:
    a. ~50% shunts across foramen ovale into the L atrium
    b. ~50% goes into the R ventricle
  4. ~90% of blood from the R ventricle goes to the pulmonary artery and is shunted across the ductus arteriousis into the aorta
    ~10% goes to the fetal lungs for perfusion
  5. After blood gets into fetal aorta and perfuses the fetus, deoxygenated blood returns to the placenta via the umbilical artery
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2
Q

Shunts blood around the liver

A

Ductus venosus

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3
Q

Why does most of the blood shunt around the lungs prior to birth?

A

-Hypoxic pulmonary vasoconstriction

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4
Q

Hole between the RA and LA

A

Foramen ovale

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5
Q

Percentage of population with patent foramen ovale

A

10-25%

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6
Q

Speed of function closure of foramen ovale

A

Rapidly after the first breath

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7
Q

Speed of anatomic closure of foramen ovale

A

3-12 months

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8
Q

Connects the pulmonary artery to the aorta

A

Ductus arteriosus

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9
Q

Functional closure of the ductus arteriosus occurs when?

A

Within the first few days

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10
Q

Complete closure of the ductus arteriosus occurs when?

A

Within 4-6 weeks

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11
Q

The ductus arteriosus is patent in ___ of the population

A

10%

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12
Q

Drugs that effect the ductus arteriosus

A
  1. PGE1 (open)
  2. Indomethacin (closes)
  3. NSAIDs (closes)
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13
Q

When are NSAIDs contraindicated?

A

During the 3rd trimester of pregnancy because they promote ductus arteriosus closure

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14
Q

Fetal circulation changes at birth

A
  1. At birth, the baby breathes and the lungs exapnd
  2. Due to increase in PaO2, blood flow to the pulmonary artery and L atrium increases, causing pressure in L atrium to increase
  3. Increased LA pressure causes the foramen ovale to close
  4. Increased aortic pressure causes the ductus arteriosus to close
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15
Q

Contained in fetal lungs at term

A

~90 mL plasma ultrafiltrate

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16
Q

When are neonates more likely to have difficulty breathing immediately after birth?

A

If their mother had a C-section rather than vaginal delivery

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17
Q

P50 for normal adult hemoglobin

A

27 mmHg

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18
Q

P50 for hemoglobin of a pregnant mother at term

A

30 mmHg

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19
Q

Normal P50 for fetal hemoglobin

A

19 mmHg

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20
Q

Fetal hypoxia etiologies

A
  1. Decrease in uterine blood flow

2. Any L shift of the mother’s oxygen hemoglobin dissociation curve

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21
Q

Causes of decrease in uterine blood flow

A
  1. Hypotension
  2. Uterine artery vasoconstriction (hypocapnea, vasoconstrictors)
  3. Uterine contractions
  4. Aortocaval compression
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22
Q

Symptoms of aortocaval compression

A
  1. Maternal hypotension
  2. Decreased maternal cardiac output/uterine blood flow
  3. Engorged epidural venous plexus (inc epidural blood volume, dec CSF volume)
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23
Q

How can you minimize aortocaval compression?

A

Place the patient in Left uterine displacement (LUD)

24
Q

When is LUD considered mandatory?

A

If the patient is >20 weeks along

25
Q

When is the first stage of labor?

A

Onset of labor all the way until maximum (10cm) cervical dilation

26
Q

2 phases of stage 1 labor

A
  1. Latent phase

2. Active phase

27
Q

During the latent phase of stage 1 labor, pain is primarily in the lower abdominal area through what innervation

28
Q

During the active phase of stage 1 labor, pain is perineal in what innervation

29
Q

When does the 2nd stage of labor occur?

A

From the time of maximum cervical dilation to the delivery of the fetus

30
Q

Heavy respirations can lead to:

A
  1. Hypocarbia

2. Possible fetal alkalosis

31
Q

When does stage 3 labor occur?

A

From delivery of the fetus to the delivery of the placenta

32
Q

CNS changes during pregnancy

A
  1. Decreased MAC requirements (up to 40%)

2. Decreased neuraxial dosing requirements

33
Q

Why is MAC requirement decreased in pregnancy?

A
  1. Endogenous opiate levels are increased

2. Progesterone levels are increased up to 20x normal

34
Q

Why are neuraxial dose requirements decreased in pregnancy?

A
  1. The fetus compresses the IVC and epidural veins become engorged
  2. The epidural venous engorgement decreases CSF volume
  3. Spinal and epidural medications have an increased cephalad spread when CSF volume is diminished, so less medication is required
35
Q

Cardiovascular changes in pregnancy

A
  1. Increased blood volume
  2. Increased cardiac output
  3. Increased clotting factor concentration
  4. Decreased SVR
  5. EKG changes (LAD)
  6. Iron anemia
36
Q

Why does cardiac output increase in pregnancy?

A
  1. A decrease in afterload (from decreased in SVR)

2. Increase in blood volume

37
Q

When can cardiac output decrease in pregnancy?

A

If the mother lays supine

38
Q

When is the greatest increase in cardiac output in pregnancy?

A

Immediately after delivery of the baby because aortocaval compression is gone

39
Q

What is a disadvantage to increased clotting factor concentration in pregnancy?

A

It increases the DVT risk up to 6-12 weeks post partum

40
Q

Safe anticoagulants in pregnancy

A

Heparin

Fibrinolytics

41
Q

Contraindicated anticoagulant in pregnancy

42
Q

What causes a decreased SVR in pregnancy?

A

Increase in estrogen and progesterone

43
Q

Why does the EKG show LAD in pregnancy?

A

Diaphragm elevation shifts the heart

44
Q

Why does iron anemia occur in pregnancy?

A

Fetus consumes iron

45
Q

Respiratory changes in pregnancy

A
  1. Hyperventilation
  2. Rapid oxygen desaturation
  3. Significant airway edema
46
Q

Why does rapid oxygen desaturation occur in pregnancy?

A

Elevated diaphragm and higher oxygen requirements

47
Q

Etiology of airway edema in pregnancy

A
  1. Weight gain
  2. Decreased intravascular oncotic pressure
  3. Progesterone
48
Q

What causes a R shift in the PaO2/SaO2 curve in pregnancy?

A

Increased 2,3 DPG levels

49
Q

GI changes in pregnancy

A
  1. Decreased LES tone
  2. Increased production of gastric acid
  3. Decreased gastric motility
50
Q

Why is the LES tone decreased in pregnancy?

A
  1. Increased progesterone levels

2. Upward displacement of the stomach by the uterus

51
Q

When is a pregnant patient generally regarded as having a full stomach?

A

After 16-20 weeks of gestational age

52
Q

ABG changes in pregnancy

A
  1. Slight increase in PaO2
  2. Slight increase in pH
  3. Slight decrease in HCO3-
53
Q

Why does PaO2 slightly increase in pregnancy?

A

Due to increased minute ventilation

54
Q

Why does pH slightly increase in pregnancy?

A

Due to respiratory alkalosis

55
Q

Why does HCO3- slightly decrease in pregnancy?

A

Due to renal compensation for respiratory alkalosis

56
Q

Renal changes in pregnancy

A
  1. GFR increases

2. Mild glycosuria/proteinuria is common

Methods of Anesthesia (20 decks)

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