4. Maternal and Fetal Physiology Flashcards
blood travels from the mothers uterine artery to?
the placenta
from the placenta where does the blood go?
through the umbilical vein into the fetal right atrium
how is blood shunted around the liver in a fetus?
ductus venosus
what are the two pathways that blood can travel after being in the fetal right atrium?
50% blood shunt through foramen ovale to left atrium
50% blood goes through right ventricle
when blood makes it to the right ventricle what two ways can it go?
90% to pulm artery and is shunted to aorta via the ductus arteriosus
10% to the fetal lungs for perfusion
why does most of the blood shunt away from the fetal lungs (other than they aren’t breathing)
they have hypoxic vasoconstriction and that decreases the amount of blood that is able to flow through the lungs
how does blood return to the placenta?
umbillical artery
foramen ovale
hole between RA and LA
what % of the population have a patent foramen ovale?
10-25%
how quickly does functional closure of the foramen ovale take after birth?
rapidly after first breath
how quickly does anatomic closing of the foramen ovale take after birth?
3-12months
ductus arteriosus
connection between the pulmonary artery and the aorta
how quickly does functional closure of the ductus arteriosus take after birth?
first few days after birth
how quickly does complete closure of the ductus arteriosus take after birth?
4-6wk
what % of the population has a patent ductus arteriosus?
10%
what drug keep the ductus arteriosus open?
prostaglandins PGE1
indomethacin
promotes ductus arteriosus closure
treats PDA after birth
NSAIDS and ductus arteriosus
promotes closure of ductus arteriosus
contraindicated in third trimester pregnancy
what are the fetal circulation changes at birth?
- baby breathes = lung expands
- PaO2 incr = vasodilation of pulm vasculature
- incr pulm blood flow
incr blood flow to LA
LAP incr - incr LAP –> foramen ovale close
- incr Aortic P –> dectus arteriosus close
what triggers foramen ovale closur
incr LAP
what triggers ductus arteriosus closure?
incr aortic pressure
Maternal/Fetal blood flow order
uterus
uterine artery
placenta
umbilical vein
RA
ductus arteriosus or foramen ovale
aorta/systemic organs
umbilical arteries
placenta
umbilical vein
how much plasma ultrafiltrate do fetal lungs have?
90mL
how does the ultrafiltrate get removed from fetal lungs?
during SVD it is squeezed out by mothers pelvic muscles
the rest absorbed by pulm capillaries and lymphatics
which are more likely to have problems with respiration after birth? SVD or C-section
C-section, no squeeze of ultrafiltrate out
P50
PaO2 that will cause SaO2 of 50%
P50 normal adult hemoglobin
27mmHg
P50 pregnant mother at term
30mmHg
P50 fetal hemoglobin
19mmHg
which is more affinitive for oxygen? fetal or maternal hemoglobin?
fetal
Aortocaval compression
pregnant patient lays supine it compresses aorta and IVC
decrease CO
decrease uterine artery blood flow (fetal hypoxia)
fetal hypoxia etiologies 2
1 decrease in uterine blood flow
2 left shift of mothers oxygen Hb curve
what can cause decrease in uterine blood flow? 4
hypotension
uterine artery vasoconstriction
uterine contractions
aortocaval compression
what can cause unterine artery vasoconstriction?
hypocapnea (hypervent)
vasoconstrictors
symptoms of aortocaval compression
maternal hypotension
decreased maternal cardiac output/uterine blood flow
engorged epidural venous plexus
supine hypotensive syndrome
when a pregnant mother is supine and gets hypotensive
(AKA Aortocaval compression)
when is left uterine displacement considered mandatory?
patient is more than 20 weeks along
stage 1 labor
onset of labor to full 10cm dilation
where is the pain during the latent phase of stage 1?
abdominal area t10-L1
where is the pain during the active phase of stage 1? why?
perineal pain S2-S4 (pudendal nerve)
fetal head press against pelvis
stage 2 labor
time of max dilation to delivery of fetus
where is the pain during stage 2 labor?
perineal area
what can heavy respirations in stage 2 labor lead to?
hypocarbia
fetal alkalosis
stage 3 labor
delivery of fetus to delivery of placenta
CNS changes for pregnant patient 2
- decreased MAC requirements (up to 40%)
2. Decreased neuraxial dosing requirements
Cardiovascular changes for pregnant patient 6
- increased blood volume
- increased cardiac output
- increased clotting factor concentration
- decreased SVR
- ECG changes (left axis deviation
- Iron anemia
respiratory changes for pregnant patient 3
- hyperventilation
- rapid oxygen desaturation
- significant airway edema
GI changes for a pregnant patient 3
- decreased lower esophageal sphincter tone
- increased production of gastric acid
- decreased gastric motility
ABG changes for a pregnant patient 3
increase in PaO2
increase in pH
decrease in HCO3-
Renal changes for a pregnant patient 2
GFR increases
mild glycosuria/proteinuria is common
why is there decreased MAC requirements for pregnant women?
endogenous opiods increased
progesterone levels are 20x normal (sedative)
why is the neuraxial dosing requirements decreased? 3
- fetus compresses the IVC
- epidural venous engorgement decreases the CSF
- spinal and epidural medications have increased cephalad spread
what is the approximate blood loss for SVD?
400-500mL
what is the approximate blood loss for a c-section?
800-1000mL
what problems does increased blood volume cause?
dilutional anemia
edema from diluted albumin
is there a greater increase in plasma or RBCs?
plasma- thats why there is dilutional anemia
what causes the edema?
plasma dilutes the albumin and decreases oncotic pressure
what are the two reasons why cardiac output increases?
decrease in afterload (decrease in SVR)
increase in blood volume
why could cardiac output decrease for a pregnant patient?
aortocaval compression from laying supine
when does the greatest increase in cardiac output occur?
immediately after delivery of baby because no more aortocaval compression
why is there increased clotting factors?
prepares mother for blood loss
what risk is increased in the hypercoaguable state?
DVT risk (up to 6-12 weeks post partum)
what are the safe anticoagulants?
heparin
finbrinolytics
what is an unsafe anticoagulant?
coumadin
what causes the decreased SVR?
increase in estrogen and progesterone
what causes the left axis deviation of the heart?
diaphragm elevation shifts the heart
what causes iron anemia?
fetus consuming Fe
vitamin supplements can be recommended
why do pregnant women hyperventilate
because increased oxygen requirements= deeper TV
what stimulates the deep breaths besides increased O2 requirements?
progesterone relaxes bronchial smooth muscle
why do mothers have an right shift of the oxyhemoglobin curve?
increased 2,3 DPG levels
causes of the airway edema in pregnant mothers?
weight gain (larger tissues) decreased oncotic pressure intravasculatly ' progesterone
what type of intubation should you avoid in pregnant mothers?
nasal intubations
why does progesterone cause airway edema??
causes capillary engorgement in the upper airway
what causes a decreased LES tone?
increased progesterone
upward displacement of stomach
at what gestational age are pregnant pts considered full stomach
full stomach after 16-20 weeks gestational age
why is there an increase in PaO2 in pregnant patients?
increased MV
why is there an increase in pH in pregnant patients
respiratory alkalosis
why is there a decrease in HCO3- in pregnant patients?
compensation for resp alk
