Fig. 3. Umbilical artery and vein blood gas values as a function of maternal inspired oxygen concentration. Administration of oxygen (fractional concentration of oxygen 0.21, 0.47, 0.74, or 1.0) to women undergoing elective cesarean delivery during epidural anesthesia resulted in a dose-related increase in partial pressure of oxygen (Po2) in both the umbilical vein (UV) and artery (UA). Maternal partial pressure of carbon dioxide (Pco2) values were, at the four inspired oxygen concentrations, respectively, 27.6 ± 1.2, 29.3 ± 0.8, 29.2 ± 1.05, and 28.6 ± 0.5 mmHg (mean ± SEM). Graph redrawn from Ramanathan et al. ,16 with permission.