Post on 12-Jan-2016
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.
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Umbilical artery (UA)Umbilical vein (UV)
Uterine arteriesUterine veinsMom
Fetus
Normal placental function: fetal and maternal circulations separated by thin membrane (syncytiotrophoblast).
“Lakes” of maternal blood
Archer TL 2006 unpublished
Fetal capillaries in chorionic villi
Precariously oxygenated environment
www.siumed.edu/~dking2/erg/images/placenta.jpgfrom Google images
www.childbirths.com/.../fetalmonitoringetc.htm
Colman-Brochu S 2004
http://www.manbit.com/OA/f28-1.htm
Manbit imageshttp://www.manbit.com/OA/f28-1.htm
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