O2 delivery to the fetus (DO2) is dependent on blood flow to the uterus, the amount of hemoglobin present in maternal blood, and percent of oxyhemoglobin (as with other organs). All three of these factors are modifiable, particularly uterine blood flow – maximize cardiac output (volume, beta agonists/increase contractility, reduction in afterload), and avoid alpha agonists. Ensure materal SpO2 of 100% (of note, increasing maternal FiO2 to PaO2 > 100 mm Hg does not appear to increase fetal SvO2, during epidural or general anesthesia [see Figure 12-6 in Datta], i.e. if SpO2 is 100%, increasing PaO2 is irrelevant)
Fetal stress responses to decreased DO2 includes bradycardia (2/2 vagal activity), increased alpha adrenergic activity, redistribution of blood (from splanchnic bed to heart, brain, placenta, adrenals), decrease in ventricular output, and decreased fetal breathing movements.
- Uterine Blood Flow: modifiable – increase cardiac output, minimize alpha activity
- Maternal Hemoglobin: modifiable (transfusion)
- % Saturation (maternal): modifiable (Ensure maternal SpO2 100%). Note that supranormal PaO2 does not seem to affect fetal SvO2 [see Figure 12-6 in Datta]