Mod VII: Maternal –Placental – Fetal Unit

Question 1

_{Maternal –Placental – Fetal Unit}

T/F: Fetal & Maternal circulations are 2 vastly different circulations

Answer 1

True

Question 2

_{Maternal –Placental – Fetal Unit​}

The complex organ present only at birth joining the maternal and fetal circulations for physiologic exchange is also known as:

Answer 2

Placenta

_{Semipermeable membrane that provides an interface for maternal and fetal circulations}

_{Composed of both maternal and fetal tissue and derives a blood supply from each}

Question 3

_{Maternal –Placental – Fetal Unit​}

The placenta is composed of both maternal and fetal tissue - How is the tissue on the maternal side called?

Answer 3

Basal plate

(tissue/spiral arteries)

Question 4

_{Maternal –Placental – Fetal Unit​}

The placenta is composed of both maternal and fetal tissue - How is the tissue on the Fetal side called?

Answer 4

Chorionic villi

(3 tissue layers, interface for the fetus)

Question 5

_{Maternal –Placental – Fetal Unit​}

What’s the name for the space separating the Basal plate and the chorionic villi? What happens in that space?

Answer 5

Intervillous space

Space separating the Basal plate and the chorionic villi

Chorionic villi/spiral arteries protrude

Maternal blood contacts fetal tissue

EXCHANGE of Respiratory gases, Nutrition, and Elimination of waste occurs

Question 6

_{Fetal Component - Umbilical-Placental Circulation}

What portion of fetal C.O. does the Umbilical-placental circulation receive?

Answer 6

50%

Question 7

_{Fetal Component - Umbilical-Placental Circulation}

What’s the rate of Fetal blood flow?

Answer 7

250 ml/min

Question 8

_{Fetal Component - Umbilical-Placental Circulation}

Describe blood flow from the fetus, through the placenta, and back to the fetus?

Answer 8

Blood enters placenta via 2 umbilical arteries → umbilical capillaries → traverse chorionic villi → cleansed/O2 → umbilical vein

Question 9

_{Fetal Component - Umbilical-Placental Circulation}

T/F: The Umbilical-Placental Circulation is a Low resistance system

Answer 9

True

Question 10

_{Fetal Component - Umbilical-Placental Circulation}

The Umbilical-Placental Circulation is a Low resistance system - What does it rely on to maintain umbilical-placental circulation?

Answer 10

Fetal CO

Question 11

_{Fetal Component - Umbilical-Placental Circulation}

Which one of these circulatory systems is autoregulated?

A. Umbilical-Placental Circulation

B. Uteroplacental circulation

Answer 11

A. Umbilical-Placental Circulation

B. Uteroplacental circulation (Not autoregulated)

Question 12

_{Fetal Component - Umbilical-Placental Circulation}

T/F: Umbilical-Placental Circulation is altered by pathophysiologic states

Answer 12

True

Question 13

_{Fetal Component - Umbilical-Placental Circulation}

Which factors affect umbilical-placental circulation?

Answer 13

Direct effects on umbilical vessels

Drug effects

Question 14

_{Fetal Component - Umbilical-Placental Circulation}

Direct effects on umbilical vessel that may affect umbilical-Placental Circulation include:

Answer 14

Cord compression/prolapse

Vasospasm from LA, vasopressors, maternal alkalosis

Increase in intervillous pressure (during uterine contraction)

Question 15

_{Fetal Component - Umbilical-Placental Circulation}

Drug that may affect Umbilical-Placental Circulation include

Answer 15

Benzodiazepines alter FHR variability

Tocolytics → fetal tachycardia

Question 16

_{Fetal Component - Umbilical-Placental Circulation}

Which drugs alter FHR variability?

Answer 16

Benzodiazepines

Question 17

_{Fetal Component - Umbilical-Placental Circulation}

Which drugs cause fetal tachycardia?

Answer 17

Tocolytics

(Tocolytics are medications used to suppress premature labor)

Question 18

_{Maternal Component - Uteroplacental Circulation}

T/F: Uteroplacental Circulation is autoregulated

Answer 18

False

Uteroplacental Circulation is not autoregulated

A drop in maternal BP will impair Uteroplacental blood flow

Increased uterine pressures during contractions will decrease Uteroplacental blood flow

Uterine vasculature remains sensitive to alpha-adrenergic agonists

Question 19

_{Maternal Component - Uteroplacental Circulation}

T/F: Uterine vasculature remains sensitive to alpha-adrenergic agonists

Answer 19

True

Question 20

_{Maternal Component - Uteroplacental Circulation}

Describe the change in uterine blood fow from nonpregnant state to term gestation:

Answer 20

UBF ↑ from 100mL/min (nonpregnant state) to

700 ml/min (term gestation; which is 20-40X’s pre pregnant)

_{[Uterine blood flow increases progressively during pregnancy from about 100 mL/minute in the nonpregnant state to 700 mL/minute (∼10% of cardiac output) at term gestation]}

Question 21

_{Maternal Component - Uteroplacental Circulation}

UBF ↑ to 700 ml/min during pregnancy - How much more is that compared to pre-pregnant uterus blood flow?

Answer 21

20-40X’s more than pre-pregnant uterus blood flow

Question 22

_{Maternal Component - Uteroplacental Circulation}

Uteroplacental Circulation Receives what portion of maternal C.O.?

Answer 22

Uteroplacental Circulation Receives 10% of maternal C.O

Question 23

_{Maternal Component - Uteroplacental Circulation}

Approximately what % of UBF perfuses the placenta?

Answer 23

80%

Question 24

_{Maternal Component - Uteroplacental Circulation}

Approximately what % of UBF perfuses the myometrium?

Answer 24

10%

Question 25

_{Maternal Component - Uteroplacental Circulation}

The smooth muscle tissue of the uterus is also known as:

Answer 25

Myometrium

Question 26

_{Maternal Component - Uteroplacental Circulation}

Why is perfusion to the uterus NOT AUTOREGULATED?

Answer 26

Uterine vascular bed maximally dilated

Question 27

_{Maternal Component - Uteroplacental Circulation}

What is uterine blood flow directly related to? What is UBF inversely related to?

Answer 27

UBF = PPP/UVR

UBF is directly r/t Placental Perfusion pressures (PPP)

UBF is inversely r/t Uterine Vascular Resistance (UVR)

_{Uterine and placental blood flow depend on maternal cardiac output and are directly related to uterine perfusion pressure and inversely related to uterine vascular resistance}

_{Decreased perfusion pressure can result from maternal hypotension secondary to hypovolemia, aortocaval compression, or sympathetic blockade and decreased systemic resistance from either general or neuraxial anesthesia}

_{Increased uterine venous pressure also can decrease uterine perfusion}

_{This can occur from supine positioning with vena caval compression, frequent or prolonged uterine contractions, or significant prolonged abdominal musculature contraction (Valsalva) during pushing}

_{Additionally, extreme hypocapnia (PaCO2 < 20 mm Hg) occasionally associated with hyperventilation secondary to labor pain can reduce uterine blood flow with resultant fetal hypoxemia and acidosis}

Question 28

_{Maternal Component - Uteroplacental Circulation}

What are Fetal O2 transfer and CO2 elimination directly r/t?

Answer 28

Placental UBF

Question 29

_{Maternal Component - Uteroplacental Circulation}

What’s the Uterine Perfusion Equation aka UBF equation?

Answer 29

UBF = (MMAP – UVP)/ UVR = PPP/ UVR

UBF: Directly proportional to MAP/PPP

UBF: Indirectly proportional to UVR

_{MMAP: maternal mean arterial pressure}

_{UVP: uterine venous pressure}

_{UVR: uterine vascular resistance}

_{PPP: placental perfusion pressure}

Question 30

_{Uteroplacental Circulation - Factors influencing UBF}

Which factors affect UBF?

Answer 30

Maternal hypotension

Alterations in uterine tone

Maternal respiratory alterations

Catecholamines (endogenous/exogenous)

IV induction agents

Inhalation agents

N20

Question 31

_{Uteroplacental Circulation - Factors influencing UBF}

Which conditions may lead to Maternal hypotension and subsequent decrease in UBF?

Answer 31

Aortocaval compression

^{↓ MMAP → ↓ UPP/PPP → ↓UBF}

^{↑ UVP → ↓ UBF}

Hypovolemia

Regional & general anesthesia

^{(more to come)}

Question 32

_{Uteroplacental Circulation - Factors influencing UBF}

Which conditions may cause Alterations in uterine tone and subsequent decrease in UBF?

Answer 32

Increased Uterine tone

^{↑ Uterine tone → ↑ UVP → ↓ UBF}

Contractions

^{Contractions → ↑ UVP → ↓ UBF}

Anesthetic drugs

^{(more to come)}

Question 33

_{Uteroplacental Circulation - Factors influencing UBF}

Which maternal blood gas alterations may result in decreased UBF?

Answer 33

SEVERE hypoxia (low PaO2)

hypercarbia (high PaCO2)

hypocarbia (low PaCO2)

Question 34

_{Uteroplacental Circulation - Factors influencing UBF}

How do Catecholamines (endogenous/exogenous) cause a decrease in UBF?

Answer 34

Catecholamines cause increased UVR

UBF = PPP/UVR

Increased UVR → ↓ UBF

Question 35

_{Uteroplacental Circulation - Factors influencing UBF}

How does Ephedrine affect UBF?

Answer 35

Alpha and beta-adrenerguc receptor stimulant

Stimulates both alpha and beta-adrenerguc receptors thus provides cardiac stimulation, w/ subsequent increase in peripheral and UBF

Traditionally drug of choice in treatment of maternal hypotension

Has no effect on actual uterine contraction

Ephedrine, which has considerable β-adrenergic activity, has traditionally been considered the vasopressor of choice for hypotension during pregnancy

However, clinical studies suggest that the α-adrenergic agonist phenylephrine is more effective in treating hypotension in pregnant patients and is associated with less fetal acidosis than ephedrine

Question 36

_{Uteroplacental Circulation - Factors influencing UBF}

How does Phenylephrine affect UBF?

Answer 36

Pure alpha-adrenergic stimulant

Pure alpha-adrenergic agents have thought to increase maternal BP at the expense of utero-placental flow

Pure alpha → uterine artery vasoconstriction →↓ UBF at high doses

Recent studies suggest there is no difference btw the use of Ephedrine or Neo

Recent studies: small doses of Phenylephrine (50ug) improve maternal hemodynamics w/ adverse effects of fetus

Phenylephrine may be safely used to treat maternal hypotension

Ephedrine or Neo have no effect on actual uterine contraction

Question 37

_{Uteroplacental Circulation - Factors influencing UBF}

What’s a potentially negative effect of giving high dose Phenylephrine?

Answer 37

Pure alpha → U_terine artery_ vasoconstriction →↓ UBF

Question 38

_{Uteroplacental Circulation - Factors influencing UBF}

T/F: Recent studies suggest there is no difference btw the use of Ephedrine or Neo

Answer 38

True

Question 39

_{Uteroplacental Circulation - Factors influencing UBF}

T/F: Recent studies: small doses of Phenylephrine (50ug) improve maternal hemodynamics w/ adverse effects of fetus

Answer 39

True

Question 40

_{Uteroplacental Circulation - Factors influencing UBF}

T/F: Phenylephrine may be safely used to treat maternal hypotension

Answer 40

True

Question 41

_{Uteroplacental Circulation - Factors influencing UBF}

T/F: Ephedrine or Neo have no effect on actual uterine contraction

Answer 41

True

Question 42

_{Uteroplacental Circulation - Factors influencing UBF}

When is the use of more potent vasoconstrictors such as Epi or NorEpi indicated?

Answer 42

Severe cases of hypotension

^{(where volume resuscitation and Ephedrine and Phenylephrine are innefective)}

Question 43

_{Uteroplacental Circulation - Factors influencing UBF}

What’s an indirect effect of IV induction agents on UBF?

Answer 43

Hypotension, which… Decreases UBF

This is an Indirect effect = Not direct effect

Question 44

_{Uteroplacental Circulation - Factors influencing UBF}

T/F: IV induction agents directly decrease UBF

Answer 44

False

IV induction agents indirectely decrease UBF

Question 45

_{Uteroplacental Circulation - Factors influencing UBF}

Eventhough there is concern for decreased UBF with administration of IV induction agents, why is it not recommended to administerd smaller doses of these agents?

Answer 45

Smaller dosing may result in light anesthesia & activation of SN

Which could cause even Greater reduction in UBF!!!

Question 46

_{Uteroplacental Circulation - Factors influencing UBF}

Smaller dosing of IV induction agents may result in light anesthesia & activation of SNS → Greater reduction in UBF. Which two induction agents are exceptions to this?

Answer 46

Ketamine

Etomidate

Question 47

_{Uteroplacental Circulation - Factors influencing UBF}

Which dose of Ketamine ↑ UBF? via which mechanism?

Answer 47

Ketamine

1.5 mg/kg → ↑MAP → ↑ UBF

_{<strong>[</strong>Ketamine in doses of less than 1.5 mg/kg does not appreciably alter uteroplacental blood flow; its hypertensive effect typically counteracts any vasoconstriction]}

Question 48

_{Uteroplacental Circulation - Factors influencing UBF}

Which dose of Ketamine ↓ UBF? via which mechanism?

Answer 48

Ketamine

> 2mg/kg → uterine hypertonicity → ↓ UBF

_{<strong>[</strong>Uterine hypertonus may occur with ketamine at doses of more than 2 mg/kg]}

Question 49

_{Uteroplacental Circulation - Factors influencing UBF​}

Which IV induction agent is recommended in the presence of hypovolemia? - Why?

Answer 49

Etomidate

(cardiovascular stability)

_{[Etomidate likely has minimal effects, but its actions on uteroplacental circulation have not been well described]}

Question 50

_{Uteroplacental Circulation - Factors influencing UBF​}

What’s the direct effect of inhalation agents on UBF?

Answer 50

Direct decrease uterine smooth muscle contractility

(Dose dependent)

Question 51

_{Uteroplacental Circulation - Factors influencing UBF​}

What’s the indirect effect of inhalation agents on UBF?

Answer 51

Indirectly decrease UBF

^{(Dose dependent)}

_{(Done via ↓ <strong>C.O./SVR</strong>→ ↓ MMAP; recall that UBF=MMAP/UVR)}

Question 52

_{Uteroplacental Circulation - Factors influencing UBF​}

In general, which dose of inhalation agents has minimal effect on UBF?

Answer 52

<1 MAC

_{<strong>[</strong>Volatile inhalational anesthetics decrease blood pressure and, potentially, uteroplacental blood flow. In concentrations of less than 1 MAC, however, their effects are generally minor, consisting of dose-dependent uterine relaxation and minor reductions in uterine blood flow]}

Question 53

_{Uteroplacental Circulation - Factors influencing UBF​}

How does N20 affect UBF when used alone?

Answer 53

Nitrous oxide alone can vasoconstrict the uterine arteries

↑ SNS activity/constant uterine contraction → ↓ UBF (theory)

Minimal effects when combined with volatile agents

_{<strong>[</strong>Nitrous oxide has minimal effects on uterine blood flow when administered with a volatile agent. In animal studies, nitrous oxide alone can vasoconstrict the uterine arteries]}

Question 54

_{Uteroplacental Circulation - Factors influencing UBF​}

Which Technique of using N2O decreases uterine atony and blood loss?

Answer 54

0.5 MAC volatile agent + N2O

Leads to decreased uterine atony and blood loss

Question 55

_{Uteroplacental Circulation - Factors influencing UBF​}

What’s the direct effect of Regional anesthesia on UBF?

Answer 55

No direct effect UBF

^{Studies proven it to be beneficial (esp. pre-eclamptic pt)}

Question 56

_{Uteroplacental Circulation - Factors influencing UBF​}

Studies have proven Regional anesthesia to be beneficial (esp. pre-eclamptic pt) in increasing UBF. How is this achieved?

Answer 56

Via ↑ intervillous blood flow

Question 57

_{Uteroplacental Circulation - Factors influencing UBF​}

What’s the indirect effect of Regional anesthesia on UBF?

Answer 57

Decrease UBF

[via sympathectomy (↓BP)]

Question 58

_{Uteroplacental Circulation - Factors influencing UBF​}

How do blood levels of Local anesthetics affect UBF?

Answer 58

↑↑↑ concentrations => uterine arterial vasoconstriction

=> ↑uterine tone => ↓ UBF

^{<strong>[</strong>High blood levels of local anesthetics—particularly lidocaine—cause uterine arterial vasoconstriction. Such levels are seen only with unintentional intravascular injections and occasionally following paracervical blocks (in which the injection site is in close proximity to the uterine arteries), and local absorption or injection into these vessels cannot be ruled out)]}

Normal serum concentration => Clinically insignificant effect

Question 59

_{Uteroplacental Circulation - Factors influencing UBF​}

There is ↓ UBF & ↑uterine tone at ↑↑↑ concentrations of local anesthetics - When is this notable?

Answer 59

Direct myometrial injection

PARACERVICAL block

Question 60

_{Uteroplacental Circulation - Factors influencing UBF​}

What are some deleterious clinical effects of PARACERVICAL block?

Answer 60

Increased LA concentration (esp. bupivacaine)

→ vasoconstriction uterine artery + ↑ uterine tone

→ ↓ UBF => FETAL BRADYCARDIA due to asphyxia

Question 61

_{Uteroplacental Circulation - Factors influencing UBF​}

Why must adverse changes in uterine perfusion pressures be addressed RAPIDLY?

Answer 61

To avoid fetal compromise!!

Question 62

_{Uteroplacental Circulation - Factors influencing UBF​}

Adverse changes in uterine perfusion pressures must be addressed RAPIDLY to avoid fetal compromise!! - How is this acheived?

Answer 62

IV fluids

LUD

Vasopressors

Avoid maternal hyperventilation