1. Tom Archer, MD, MBA January 31, 2012
Threats to fetal oxygenation during labor– what is the context of your epidural?
Tom Archer, MD, MBA
January 31, 2012

2. The fetus floats at the far end of a tunnel of oxygen delivery.
If the tunnel is blocked, the fetus dies.

3. Systematic approach to thinking about the “risk context” of an epidural
We can do the “usual things” directly related to hypotension more intelligently (fluids, pressors, LUD, O2.
Think about “less usual things” (hyperstimulation, nuchal cord, pre-existing disease that make patient more precarious.
Epidural may only be tangentially “to blame”– or not at all!

4. The fetal oxygen supply is precarious– both on the fetal and maternal sides of the placental interface
med.yale.edu

5. Fetal-side (umbilical cord) problems with fetal oxygen supply

6. Nuchal umbilical cord

7. Knotted umbilical cord

8. Vasa previa– fetal blood vessels between presenting part and cervix– will rupture as presenting part descends.

9. Prolapsed umbilical cord

10. Maternal-side threats to fetal oxygen supply

11. Fetal O2 supply Figure 1 Healthy, abundant uteroplacental perfusion
Upper body
Minimal collateral venous return to heart via lumbar and azygos system
Uncompressed aorta and iliac arteries
Open IVC
Fetal O2 supply

12. Fetal O2 supply Uterine contractions
Figure 2 Uterine contractions periodically deprive placenta of perfusion.
Upper body
Uncompressed aorta and iliac arteries
Open IVC
Minimal collateral venous return to heart via lumbar and azygos system
Fetal O2 supply
Uterine contractions

14. ACC ACC Uterine contractions Uterine mass Fetal O2 supply
Figure 3 Aortocaval compression reduces placental perfusion pressure.
Upper body
Increased collateral venous return to heart via lumbar and azygos system
Compressed IVC
Compressed aorta and iliac arteries
ACC
Uterine mass
ACC
Fetal O2 supply
Uterine contractions

15.
Manbit images

17. Ballas, Mantell, Archer SOAP 2012

20. Both positive pressure ventilation and uterine contractions in the presence of free venous return cause the heart to receive periodic increases in venous return.
Could these periodic volume challenges shed light on the parturient’s “volume status?”
Michard

21. Placental vascular disease
Figure 4 Placental vascular disease (e.g. preeclampsia) further reduces placental perfusion.
Upper body
Increased collateral venous return to heart via lumbar and azygos system
Compressed IVC
Compressed aorta and iliac arteries
ACC
ACC
Uterine mass
Fetal O2 supply
Uterine contractions
Placental vascular disease

22. Pre-eclampsia: ischemic chorionic villi release pre-E mediators into maternal blood.
Say “OUCH!”
Pre-E
mediators
Poor placentation

23. Poor-placentation theory of pre-E:
Synciotrophoblast invades myometrium but does not denervate spiral arteries of mother properly.
Hence, intervillous flow is sub-optimal.
Chorionic villi are ischemic and release mediators (VEGF, etc) which damage maternal endothelium.

24. Placental spiral artery disease Placental abruption or thrombosis
Figure 5 Placental abruption reduces placental volume available for gas exchange
Upper body
Increased collateral venous return to heart via lumbar and azygos system
Compressed IVC
Compressed aorta and iliac arteries
ACC
ACC
Uterine mass
Fetal
O2 supply
Uterine contractions
Placental spiral artery disease
Placental abruption or thrombosis

25. Placental abruption decreases placental area available for gas exchange.

26. Epidural reduces arterial blood pressure
Figure 6 Epidural may be “straw that breaks camel’s back” and causes “fetal distress”.
Epidural reduces arterial blood pressure
Upper body
Increased collateral venous return to heart via lumbar and azygos system
Compressed IVC
Compressed aorta and iliac arteries
ACC
ACC
Uterine mass
Fetal
O2 supply
Uterine contractions
Placental vascular disease
Placental abruption or thrombosis

27. “Routine” epidural.

28. Your next epidural
Ask yourself, “What are the pre-existing threats to fetal oxygenation in my patient?”
“What special precautions should I take to prevent fetal hypoxia in this patient?”
Be attentive to hyperstimulation, preeclampsia, abruption, hypotension, etc.

29. The End