Class,
In order to understand the fetal response to the lack of oxygenation, you need to understand the oxygenation pathway to the fetus. Oxygen is transferred from the environment to the fetus by maternal and fetal blood along a pathway that includes the maternal lungs, heart, vasculature, uterus, placenta, umbilical cord, and fetus.
ENVIRONMENT
↓
MATERNAL LUNGS
↓
HEART
↓
VASCULATURE
↓
UTERUS
↓
PLACENTA
↓
UMBILICAL CORD
↓
FETUS
Summary of the Oxygen pathway and causes of interrupted oxygen transfer
Oxygen Pathway | Causes of interrupted oxygen transfer |
Lungs | Respiratory depression (narcotics, magnesium sulfate) Apnea, seizures (eclampsia) Pulmonary embolus, pulmonary edema Pneumonia, ARDS Asthma, atelectasis |
Heart | Decreased cardiac output Hypovolemia Compression of the inferior vena cava Regional anesthesia (sympathetic blockade) Cardiac arrythmias |
Vasculature | Hypotension Hypovolemia Compression of the inferior vena cava Regional anesthesia(sympathetic blockade) Medications (hydralazine, labetalol, nifedipine) |
Uterus | Excessive uterine activity Uterine stimulants (prostaglandins, oxytocin) Uterine rupture |
Placenta | Placental separation Rarely vasa previa Rarely fetal-maternal hemorrhage Placental infarct, infection (usually confirmed retrospectively) |
Umbilical cord | Cord compression Cord prolapse “True” knot |
Please post your comments and questions.
Next module, I will be discussing the fetal response to interrupted oxygenation.
Miller, L. (2008). Electronic fetal monitoring. HANYS Obstetric Safety Initiative. Train the trainer power point presentation.
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