Burke, Ob Lecutre Ii

Front 1

What perfuses the placenta and uterus?

Back 1

the uterine and ovarian arteries

Front 2

Uterine blood flow is what before pregnancy?
What is it at term?

Back 2

50-100ml/min before pregnancy

700-900ml/min at term

Front 3

What is cardiac output before pregnancy and at term?

Back 3

CO before pregnancy is <5%
CO at term is 10-12%

Front 4

Does the placenta self regulate what the blood flow?

Back 4

No, uterine blood flow is not autoregulated. The uterine vascular bed is almost maximally dilated under normal conditions. Flow is proportional to the mean uterine perfusion pressure.
Moms BP dictates uterine blood flow and perfusion

Front 5

What is the UBF calculation?

Back 5

UBF = aterial pressure – venous pressure uterine Over vascular resistance

Front 6

What increases uterine vascular resistance?

Back 6

contractions

Front 7

If venous pressure goes up, what happens to UBF?

Back 7

UBF goes down

Front 8

As perfusion pressure goes down, blood flow goes....?

Back 8

down (mom's Bp)

Front 9

As uterine vascular resistance goes up, blood flow goes...?

Back 9

down

Front 10

What are some causes of decreased uterine blood flow?

Back 10

decrease uterine arterial pressure

increased uterine venous pressure

endogenous vasoconstrictors

exogenous vasoconstrictors

Front 11

Give examples of decreased arterial blood flow

Back 11

supine position

hemorrhage/hypovolemia

hypotension (drugs or sympathetic block)

Front 12

Give examples of increased uterine venous pressure

Back 12

vena caval compression

uterine contractions

hypertonus (drug induced - pitocin)

skeletal muscle hypertonus (seizures, valsalva)

Front 13

Give some examples of endogenous vasoconstrictors

Back 13

catecholamines, vasopressin

Front 14

Give some examples of exogenous vasoconstrictors

Back 14

epinephrine, phenylephrine > ephedrine, locals

Front 15

Other reasons for Uteroplacental blood flow problems

Back 15

severe hypoxia

hypercarbia

hypocarbia = alteration in uterine vascular resistance

Front 16

Why should we avoid hyperventilating a pregnant woman?

Back 16

hyperventilation of Paco2 to 18-20mmHg causes vasocontriction of uterine artery = decreased uterine blood flow = fetal hypoxia and acidosis

Front 17

What is the purpose of the placenta?

Back 17

It provides all nutrients to the fetus. It allows for the physiologic exchange between maternal and fetal tissue

Front 18

Fetal Blood

Back 18

Comes from 2 umbilical arteries that divide into small vessels in villi

Capillaries in villi allow gas exchange with maternal blood

Fetal blood flows through villi

Collects into single umbilical vein that carries nutrient-rich blood to fetus

Front 19

Maternal Blood

Back 19

Enters basal place of placenta via uterine arteries (branch into spiral arteries in endometrium)

thru chorionic plate

spurts into intervillous space where nutrients are exhanged with fetal blood (in villi)

drains thru beins in basal plate

Front 20

3 microscopic tissue layers separate fetal and maternal blood...name them

Back 20

1) Fetal trophoblast (cytotrophoblast, syncytiotrophoblast - the metabolically active part)

2) fetal connective tissue (supports villi)

3) endothelium of fetal capillaries

Front 21

Describe characteristics of the placenta

Back 21

disc shaped, weighs approx 500grams

2 umbilical arteries

1 umbilical vein

villous surface area of term placenta = 11 m2

area of exchange (vasculosyntytial membrane area) = 1.8 m2

Front 22

Name the 5 mechanisms of placental exchange

Back 22

1) diffusion (active or facilitated)
2) active transport
3) bulk flow
4) pinocytosis
5) breaks in the villi (might allow fetal blood into maternal circulation)

Front 23

Passive diffusion

Back 23

O2, CO2, small ions, fatty acids, narcotics and locasl

Depends on concentration gradient, electrochemical difference, MW, lipid solubility, degree of ionization, membrane surface area and thickness

Front 24

Facilitated diffusion

Back 24

rate of diffusion is greated than concentration gradient. (carrier molecule)

Front 25

Active Transport

Back 25

transfer against concentration gradient

amino acids, water-soluble viatmins, larger ions (Ca++, and Fe++)

Front 26

Bulk Flow

Back 26

Passage due to hydrostatic or osmotic gradient

water, solutes

Front 27

Pinocytosis

Back 27

molecules transported in small vesicles made up of cell membranes

immune globulins

Front 28

Breaks

Back 28

villi may break allowing contents to pass into maternal circulation

fetal Rh-positive cells

Front 29

*If Mom is RH- and dad fetus are RH+:

Back 29

mom has no Rh+ antibodies but will develop them if exposed to Rh + blod from break in placenta. (some fetal blood normall gets into mom's system at birth).

These antibodies will destroy RBCs in future fetus'

Erythroblastosis fetalis

Treatment - RhoGam at 26-18 weeks and within 72 hours after birth or miscarriage

Front 30

How much O2 does a term fetus have?

Back 30

42ml of O2 in body

Front 31

The fetus uses about how much O2 per minute?

How long will the O2 last?

Back 31

Uses about 21 mL/min

Only 2 min of O2????? (no - irreversible brain damage after about 10 min)

In animals, uterine flow can decrease by about 50% before we see severe fetal acidosis (if normal preg.)
Redistribution of flow in fetus to vital organs leads to decrease in O2 consumption

Front 32

Is it common that total O2 interruption occurs?

Back 32

Total interruption of O2 rare

Front 33

What are some of the components of placental and gas exhange of O2 from mom to fetus?

Back 33

Intervillous blood flow
Fetal-placental blood flow
Mom’s affinity for O2, PaO2, Hgb
Baby’s affinity for O2, PaO2, Hgb
Placental diffusing capacity
Placental O2 consumption
Mom & baby’s pH and PaCO2

Front 34

What are the most important components of placental exchange?

Back 34

Rates of blood flow on each side
Area available for exchange

Front 35

What are other things you can do to enhance O2 exchange?

Back 35

Keep mom’s B/P up
Manage contractions
Careful with Pitocin
Watch for UP compromise

Front 36

You should remember to keep mom's BP up in order to have good placenta & gas exhange. When should you treat mom's BP?

Back 36

Treat mom's BP if it gets less than 100mmHg systolic

Front 37

When you have decrease size in the placenta, what are some of the reasons?

Back 37

Maternal hypertension
Intrauterine infections
Congenital defects
Abruptio placenta
Acute decrease
Fetal survival depends on how large

Front 38

When you have increase in the size of the placenta, what are some of the reasons?

Back 38

Maternal diabetes
Erythroblastosis fetalis

Front 39

What are some of the effects of anesthesia on uterine blood flow?

Back 39

Decreases with positive pressure ventilation
Drugs
Affect on uterus usually from altered maternal B/P
Volatiles
Reduced – dose dependent
Induction agents
May reduce – may be reduced from increased uterine vascular resistance from catecholamines with light anesthesia
Ketamine
Up to 1 mg/kg OK

Front 40

What are some of the effects of regional anesthesia on uterine blood flow?

Back 40

Increase in uterine blood flow when
Pain relieved
Decreased sympathetic activity
Decreased maternal hyperventilation
Decrease in uterine blood flow when
Hypotension results
Unintentional IV injection of local or epi
Absorbed local (little effect)

Front 41

How do you measure uterine activity?

Back 41

Uterine activity determined by frequency and strength of contractions and pressure generated by contractions
Measured indirectly by tocodynamometer (external)
Triggered by changing shape of uterus during contraction
Measured directly (internally) by intrauterine pressure catheter inserted into uterine cavity

Front 42

Describe first stage of labor

Back 42

Beginning of cervical dilation and effacement to full dilation
Latent phase (early dilation) or active phase (contractions regular, every 5 min., dilation 4-10 cm)

Front 43

What is second stage of labor?

Back 43

Complete dilation to delivery of infant

Front 44

What is the third stage of labor?

Back 44

Delivery of infant until placenta is delivered

Front 45

When you have abnormal progress of labor you might have a prolonged latent phase. What does this mean and what might it be caused by?

Back 45

It means effacement and softening of cervix.
May be caused by
Incoordinate contractions
Excessive sedation or anesthesia
May see Pitocin started to augment contractions

Front 46

If you have a protracted active phase, what might you see?

Back 46

Cephalic-pelvic disproportion
Malposition
Malpresentation

Front 47

What are some other abnormal progress of labor issues?

Back 47

Active phase arrest
Protractred descent
Arrest of descent
Uterine relaxation

Front 48

Describe stations of the fetal head

Back 48

Relation of presenting part to ischial spines of pelvic inlet

Want 0 or + numbers

Don’t want “ballotable” head

Front 49

Describe some effects of Anesthesia on Uterine Activity

Back 49

Inhalation agents
All cause dose-related relaxation of uterus (limited studies on Des and Sevo)
Keep concentration < 1 MAC
Don’t exceed 0.5% MAC until after delivery
Higher concentrations may interfere with oxytocin effect on uterus
Normotension and LUD prevents ill effects
Low dose inhalation not associated with increased blood loss or decreased uterine tone

Front 50

Describe effects of Nitrous and Ketamine on uterine activity

Back 50

Nitrous Oxide
Little or no effect on uterus
60-70% required for amnesia
Don’t administer > 50% until after delivery
Ketamine (increase in SNS activity)
Slight increase in uterine tone in small doses
< 0.25 mg/kg will not depress fetus
> 1.1 mg/kg may cause decreased perfusion to point of depression of fetal scores (OK up to 1 mg/kg)

Front 51

What about regional anesthesia? What are its effects on uterine activity?

Back 51

Improper technique will slow labor
One agent not more so than others
Some think use of epi will slow contractions
T-10 block during stage 1 will not affect labor if
Preload with 20cc/kg IVF (avoid hypotension)
Avoid aortocaval syndrome (15° LUD)
Limit dose to essential amount

Front 52

What about epidurals? What effect will it have on labor?

Back 52

Epidural will slow labor if
Excessive concentrations are used
Some debate that epidurals:
May remove urge to push in 2nd stage
Higher rate of forceps delivery
Higher C-section rate
Increased incidence of fetal malposition

Front 53

Uterius has what kind of receptors? What happens when they are stimulated?

Back 53

Uterus has alpha and beta receptors
Alpha stimulation – uterine hypertonus
Beta stimulation – uterine relaxation

Front 54

What are the effectsof phenylephrine on uterine activity?

Back 54

Debate continues regarding effect on uterine artery
Most sources say OK
Titrate in small increments (20-100mcg/dose)
Start with Ephedrine

Front 55

Whats the effect of Ephedrine?

Back 55

No effect on uterine activity
Does not reduce uterine blood flow

Front 56

What's the effect of epinephrine in locals?

Back 56

Effects on labor debated
Increases uterine activity
Increases need for oxytocin augmentation
Does not improve activity of bupivacaine
Some say that it should be avoided especially in patients with compromised uterine blood flow

Front 57

How do you choose which vasopressor to use?

Back 57

Vasopressor to use is dictated by HR.
Ephedrine causes more fetal acidosis than neo

Front 58

How much neo should you start with?

Back 58

start with 50mcg of neo at a time. If too much, you can constrict the uterine artery