O2 delivery to fetus in labor

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.

Fetal DO₂

• 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].