Uterine blood flow
and tocolysis
Tom Archer, MD, MBA
UCSD Anesthesia
Uterine blood flow (UBF)
• Fetal O2 supply depends on adequate perfusion
of placental lacunae.
• Adequate perfusion requires high inflow
pressure and low outflow pressure  avoid
aorto-caval compression with LUD.
• UBF stops during uterine contraction  need to
avoid hyperstimulation from too much oxytocin.
)
Normal placental function: fetal and maternal circulations separated by thin
membrane (syncytiotrophoblast).
Umbilical artery (UA)
Umbilical vein (UV)
Fetus
“Lakes” of
maternal blood
Fetal capillaries
in chorionic villi
Precariously oxygenated environment
Uterine veins
Mom
Archer TL 2006 unpublished
Uterine arteries
www.siumed.edu/~dking2/erg/images/placenta.jpg
from Google images
www.childbirths.com/.../fetalmonitoringetc.htm
Colman-Brochu S 2004
http://www.manbit.com/OA/f28-1.htm
http://www.manbit.com/OA/f28-1.htm
Manbit
images
Chestnut chap. 2
Short term: Why increase
uterine tone?
• Stop placental implantation site from
bleeding.
– Let baby breast feed nipple stimulation
causes oxytocin release from posterior
pituitary.
– Exogenous oxytocin (causes hypotension)
– Methylergonovine (Methergine). No in HBP.
– Carboprost (Hemabate). No in asthma /
COPD. May cause diarrhea.
Short term: Why decrease
uterine tone?
• Entrapped placenta (uterus has contracted with
placenta or fragments inside).
• Retained placenta will not allow uterus to fully
contract  continued bleeding.
• Methods to relax uterus (for manual removal):
–
–
–
–
Traditional: halothane anesthesia (+ETT)
Probably better: IV or SL NTG.
NTG also helps placenta to separate
How about a spinal or epidural? What will they do?
Not do?
Tocolysis
• Current OB practice:
– no tocolytics after 34 weeks (because 34 weekers do
very well)
– If membranes are ruptured, don’t delay delivery
(chorioamnionitis  neurological injury to fetus).
– Does tocolysis improve outcomes before 34 weeks?
You can delay delivery, but are you accomplishing
anything? We don’t know.
Hauth JC Semin Perinatol 30:98-102 © 2006
Tocolysis: Why decrease
uterine tone?
• Allow time for betamethasone to promote lung
maturation (before 33 weeks).
• Does tocolysis before 34 weeks improve
outcomes?
• Maybe not.
• If membranes are ruptured, delaying delivery
may allow chorioamnionitis and fetal damage
Management of spontaneous
preterm labor
• < 33 weeks, steroids.
• < 34 weeks consider tocolysis
• < 37 weeks, group B strep prophylaxis
Hauth JC Semin Perinatol 30:98-102 © 2006
Tocolytics
• Ethanol (historical interest).
• MgSO4– NOT!
• And, >50 gm MgSO4 associated with neonatal brain
damage (IVH) (Mittendorf R Journal of Perinatology (2006) 26, 57–63).
• Beta agonists (terbutaline, ritodrine). Pulmonary
edema, tachycardia, hypotension, anxiety
• Cyclooxygenase inhibitors (indomethacin)
• Ca++ channel antagonists (nifedipine)– 1st line drug
• Oxytocin antagonists (atosiban)—1st line drug
Hauth JC Semin Perinatol 30:98-102 © 2006