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

The fetus floats at the far end of a tunnel of oxygen delivery. If the tunnel is blocked, the fetus dies. http://darksideofthecatalogue.wordpress.com/2011/11/22/light-at-the-end-of-the-tunnel-is-glowing-thing-23-12/

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!

The fetal oxygen supply is precarious– both on the fetal and maternal sides of the placental interface med.yale.edu http://www.spiralzoom.com/Science/SpiralsHumanBody/SpiralsHumanBody.html

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

Nuchal umbilical cord http://library.med.utah.edu/WebPath/PLACHTML/PLAC002.html

Knotted umbilical cord http://library.med.utah.edu/WebPath/PLACHTML/PLAC010.html

Vasa previa– fetal blood vessels between presenting part and cervix– will rupture as presenting part descends. http://midwifemuse.wordpress.com/2008/02/27/vasa-previa/

Prolapsed umbilical cord http://www.empowher.com/media/reference/umbilical-cord-prolapse

Maternal-side threats to fetal oxygen supply

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

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

http://www.birthinjury-legalinfo.com/injury_asphyxia.html

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

http://www.manbit.com/OA/f28-1.htm Manbit images

http://www.manbit.com/OA/f28-1.htm

Ballas, Mantell, Archer SOAP 2012

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

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

Pre-eclampsia: ischemic chorionic villi release pre-E mediators into maternal blood. Say “OUCH!” Pre-E mediators Poor placentation www.siumed.edu/~dking2/erg/images/placenta.jpg

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. http://pharyngula.org/images/preeclampsia_model.jpg

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

Placental abruption decreases placental area available for gas exchange. http://emedicine.medscape.com/article/252810-overview

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

“Routine” epidural. http://www.macllp.com/child_birth_anesthesia/epidural_ad.cfm

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.

The End