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OB > Maternal and fetal physiology > Flashcards

Maternal and fetal physiology Flashcards

1
Q

How much does mean maternal weight increase by during pregnancy?

A

Increases by 17%, or roughly 12kg

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2
Q

How much do the uterus, amniotic fluid, etc weigh?

A

uterus - 1kh
amniotic fluid - 1 kg
blood volume/interstitial fluid - 2kg
deposition of new fat and protein - 4kg

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3
Q

Cardiovascular changes in pregnancy

A

Increased heart size due to increased blood volume and increased stretch and force of contraction

Changes in heart sounds

Cardiac output increases by 5 weeks gestation and is 35-40% above baseline by the end of 12 weeks

Strove volume increases by 20% in the 1st trimester and 25-30% in the 2nd trimester (correlated with increased estrogen levels)

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4
Q

What happens to the heart rate during pregnancy?

A

Heart rate steadily increases (15-20% above baseline) during 1st and 2nd trimesters – both the PR interval and uncorrected Qt interval are shortened

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5
Q

What happens to skin blood flow?

A

At term skin blood flow is 3-4x higher than nonpregnant levels

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6
Q

What is aortocaval compression? (supine hypotension syndrome)

A

It typically occurs in pregnant females, usually after 20 weeks of gestation, when the patient is in the supine position. Blood flow from the lower extremities back to the maternal heart and central circulation is impeded due to the uterus compressing the inferior vena cava and aorta

Blood returns from the lower extremities through intraosseous, vertebral, paravertebral and epidural veins; however, the collateral return is not as great resulting in decreased right atrial pressure. Supine position at term 10-20% decline in stroke volume and cardiac output.

Beginning at mid-pregnancy, assumption of the supine position may result in compression of the inferior vena cava and aorta by the gravid uterus, which may result in decreases in both cardiac output and uteroplacental perfusion. Severe hypotension and bradycardia in the supine position is called the supine hypotension syndrome.

Pregnant women should not lie supine after 20 weeks’ gestation without aggressive maintenance of baseline blood pressure. The uterus should be displaced to the left by placement of a wedge underneath the right hip or by tilting the operating table, or the pregnant women should assume the full lateral position.

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7
Q

How much can stroke volume and cardiac output decrease in the supine position with aortocaval compression?

A

10-20%

With regional anesthesia - profound hypotension

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8
Q

How can you avoid supine hypotension syndrome?

A

The uterus should be displaced by placing a rigid wedge under the right hip and tilting the table left side down

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9
Q

Cardiac changes during labor and postpartum

A

Cardiac output increases from pre-labor values by approx. 10% in the first stage to 25% in the late first stage, 40% by second stage of labor

Immediate post-partum period as much as 75% above predelivery measurements and 150% above pre-pregnancy baseline

Postpartum increase is from relief of vena caval compression, diminished lower extremity venous pressure, sustained myocardial contraction, and loss of the low-resistance placental circulation

Cardiac output decreased to just below pre-labor values at 24 hrs. postpartum and returns to pre-pregnancy between 12-24 weeks postpartum

a right shift in the oxyhemoglobin dissociation curve.

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10
Q

What is Relaxin?

A

the hormone responsible for relaxation of the pelvic ligaments, causes relaxation of the ligamentous attachments to the lower ribs

Capillary engorgement of the larynx and the nasal and oropharyngeal mucosa begins early in the first trimester and increases progressively throughout pregnancy

estrogen on the nasal mucosa may cause symptoms of rhinitis and epistaxis

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11
Q

Is dyspnea common during pregnancy?

A

Yep!

Dyspnea is a common complaint during pregnancy, affecting up to 75% of women. Contributing factors include:
increased respiratory drive
decreased Paco2
increased oxygen consumption from the enlarging uterus and fetus
larger pulmonary blood volume
anemia
nasal congestion

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12
Q

Does exercise have any effect on pregnancy induced changes in ventilation?

A

Nope.

The hypoxic ventilatory response is increased during pregnancy to twice the normal level, secondary to elevations in estrogen and progesterone levels.84 This increase occurs despite blood and cerebrospinal fluid (CSF) alkalosis

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13
Q

Are FEV1 and FVC and flow-volume loops and closing capacity changed with pregnancy?

A

No

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14
Q

Is diaphragm excursion changed?

A

It’s increased

Also, pulmonary resistance is decreased

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15
Q

Is ventilation overall increased or decreased?

A

Increased

Respiratory rate increased 15%
Tidal volume is increased 40%
Minute ventilation increased 50%

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16
Q

Ph and co2 changes

A

PaCO2 decreased to 28-32 mm Hg secondary to hyperventilation ie: resp. alkalosis
Compensatory metabolic acidosis by excretion of Bicarbonate maintains normal ph

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17
Q

What is one VERY important thing about induction for OB patients?

A

ALL INTUBATIONS/GENERAL ANESTHESIA ARE Rapid Sequence Inductions!!!

USE SMALLER ENDOTRACHEAL TUBE (6.5) AND AVOID NASAL INTUBATION OR INSTRUMENTATION

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18
Q

Are pregnant women prone to hypoxia during general anesthesia?

A

YES! Must pre-oxygenate very well

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19
Q

P50 of hemoglobin _____ from 27 to _____ mmHg

A

P50 of hemoglobin increases from 27 to 30 mmHg, which Aids delivery of oxygen to fetus.

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20
Q

Respiratory highlights

A

No change to vital capacity, total lung capacity.
Decreased FRC, coupled with increased maternal oxygen consumption, can rapidly lead to maternal hypoxia during induction of GA.

Decreased physiological dead space.

Slight decrease in airway resistance.

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21
Q

Expanding uterus displaces diaphragm ______
FRC _______ by ~20%.
Potential for small airway closure.

A

Expanding uterus displaces diaphragm cephalad (towards the head) FRC decreases by ~20%.
Potential for small airway closure.

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22
Q

Gastrointestinal

A

Stomach is displaced by uterus resulting in reduced competence of gastroesophageal sphincter.

Progesterone decreases gastroesophageal sphincter tone.

Placental gastrin secretion increases acid secretion

Slowed gastric emptying is controversial.

Net effect of the above is that most patients have gastric fluid of greater than 25 cc w/ a pH of less than 2.5 and are thus at increased risk of symptomatic aspiration.

ALL GENERAL ANESTHESIA IS A RSI

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23
Q

Renal blood flow and glomerular filtration are ______ by about ___% by 16th week, remains elevated until delivery.

A

Renal blood flow and glomerular filtration increased by about 50% by 16th week, remains elevated until delivery.

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24
Q

Are Serum BUN and creatinine mildly increased or decreased?

A

decreased

25
Q

True/false: Mild glycosuria and proteinuria are common.

A

true

26
Q

Are pregnant women hypercoagulable?

A

Yep. Increased risk of P.E

27
Q

What are the most common musculoskeletal complaints?

A

Back pain and leg pain are the most common concerns/complaints

28
Q

Is MAC increased or decreased with pregnancy?

A

decreased

29
Q

Cerebrospinal fluid volumes are _______ and epidural veins are engorged

A

Cerebrospinal fluid volumes are decreased and epidural veins are engorged

30
Q

Do pregnant women have greater sympathetic tone than nonpregnant women?

A

Yes

31
Q

What acid-base balance occurs throughout pregnancy?

A

partially compensated respiratory alkalosis

32
Q

True/false: Gastric volume, emptying, and pH are unaltered during pregnancy, but lower esophageal sphincter tone may be reduced with increased risk for gastroesophageal reflux.

A

True

33
Q

A few other key points

A

Pregnant women have a rapid decrease in Pao2 during periods of apnea.

Pregnant women are at increased risk for failed tracheal intubation.

Pregnant women are less responsive to vasopressors than nonpregnant women.

34
Q

Diffusion (passive transport)

A

drugs with less than 600 Da cross the placenta

35
Q

Bulk flow

A

Bulk flow – Similar to Active transport but requires greater energy and is considered “Facilitated Transport”. This mode of transport exhibits: 1. saturation kinetics 2. competitive and noncompetitive inhibition 3. stereospecificity 4.temperature influences

36
Q

Active transport

A

Movement of any substance across a cell membrane requiring energy from ATP hydrolysis

37
Q

Pinocytosis

A

An energy requiring process in which the cell membrane invaginates around large macromolecules that exhibit negligible diffusion properties

38
Q

Breaks

A

an example is when the mother has preeclampsia it may alter the net placental transport

39
Q

How much O2 must the placenta provide?

A

The placenta must provide 8ml O2/min/kg for fetal body weight for fetal growth and development while adults require 3-4ml O2/min/kg at rest

40
Q

Where does oxygen has the smallest storage to utilization ratio in?

A

the fetus

41
Q

What is placental PAo2?

A

40 mmHG

To compensate for this the fetal oxy-hemoglobin dissociation curve is left shifted and the maternal curve is right shifted.

Fetal hemoglobin is also higher than maternal.

42
Q

Placental Transfer of CO2

A

Occurs by simple diffusion across the placenta.

Fetal Hgb has a lower affinity for CO2 than maternal.

43
Q

During pregnancy, anatomic adaptations result in substantial (near-maximal) vasodilation of the uterine spiral arteries; this leads to a low-resistance pathway for the delivery of blood to the placenta. Therefore, adequate uteroplacental blood flow depends on the maintenance of a normal maternal perfusion pressure.

A

During pregnancy, anatomic adaptations result in substantial (near-maximal) vasodilation of the uterine spiral arteries; this leads to a low-resistance pathway for the delivery of blood to the placenta. Therefore, adequate uteroplacental blood flow depends on the maintenance of a normal maternal perfusion pressure.

44
Q

Can fetal acidemia result in the “ion trapping” of both local anesthetics and opioids?

A

Yep

45
Q

Lipophilicity and drug depot

A

Lipophilicity, which enhances the central nervous system uptake of general anesthetic agents, also heightens the transfer of these drugs across the placenta. However, the placenta itself may take up highly lipophilic drugs, thereby creating a placental drug depot that limits the initial transfer of drug.

46
Q

What is the hallmark for fetal well-being?

A

Maintenance of uteroplacental blood flow

47
Q

How much of cardiac output goes to uterine blood flow?

A

10%

48
Q

What three factors affect uterine blood flow?

A

Systemic blood pressure
Uterine vasoconstriction
Uterine contractions

49
Q

Anesthesia and UBF

A

Propofol and thiopental: mildly reduce UBF via maternal hypotension.

Ketamine has no net effect at doses <1.5 mg/kg.

Volatile agents dec. UBF secondary to hypotension but at < 1 MAC the effect is minor.

Nitrous oxide has negligible effects.

Opioids have little effect.

High serum local anesthetic levels can result in uterine vasoconstriction.

50
Q

Uterine blood flow may improve with _____ _______ as a reduction in maternal catechol levels reduces vasoconstriction, as long as normal blood pressure is maintained.

A

Uterine blood flow may improve with neuraxial analgesia as a reduction in maternal catechol levels reduces vasoconstriction, as long as normal blood pressure is maintained.

51
Q

Stages of labor

A

Normal labor starts 40 +/-2 weeks after LMP

1st stage: onset of true labor until complete cervical dilatation.

 Latent phase: minor dilation 2-4 cm, infrequent 
 contractions.

 Active phase: progressive dilation to 10 cm and 
 regular contractions (3-5 min).

2nd stage: time from complete dilation until infant delivered.

3rd stage: time from delivery of infant until placenta delivered.

52
Q

What are decelerations in labor?

A

temporary decreases in the fetal heart rate (FHR) during labor

Normal to have decelerations when the baby is coming down the vaginal canal.

not normal for extended periods of time or with uteroplacental insufficiency & umbilical cord compression.

53
Q

What is the method most commonly used clinically to assess uteroplacental blood flow in humans?

A

Doppler ultrasonography

54
Q

What three three anatomic communications characterize fetal blood flow?

A

the ductus venosus, the foramen ovale, and the ductus arteriosus

55
Q

Fetal Circulation

A

Oxygenated blood leaves the placenta via the fetal umbilical vein (1), enters the liver where flow divides between the portal sinus and the ductus venosus, and then empties into the inferior vena cava (2). Inside the fetal heart, blood enters the right atrium, where most of the blood is directed through the foramen ovale (3) into the left atrium and ventricle (4), and then enters the aorta. Blood is then sent to the brain (5) and myocardium, ensuring that these cells receive the highest oxygen content available. Deoxygenated blood returning from the lower extremities and the superior vena cava (6) is preferentially directed into the right ventricle (7) and pulmonary trunk. The majority of blood passes through the ductus arteriosus (8) into the descending aorta (9), which in turn supplies the lower extremities (10) and the hypogastric arteries (11). Blood returns to the placenta via the umbilical arteries for gas and nutrient exchange. A small amount of blood from the pulmonary trunk travels through the pulmonary arteries (12) to perfuse the lungs. Arrows in this figure depict the direction and oxygen content [white (oxygenated), blue (deoxygenated)] of the blood in circulation.

56
Q

Fetal swallowing

A

Fetal swallowing plays an important role in amniotic fluid homeostasis, and the swallowed fluid appears to provide nutritional support for mucosal development within the gastrointestinal tract.

57
Q

When is surfactant made?

A

The pulmonary surfactant system is one of the last systems to develop before birth. Surfactant assembly occurs in the type II alveolar cells, and components of surfactant are first detected between 24 and 28 weeks’ gestation.

58
Q

Acute hypotension in the fetus stimulates a reflex response, which includes both _____ and _______.

A

Acute hypotension in the fetus stimulates a reflex response, which includes both bradycardia and vasoconstriction.

OB (6 decks)

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