Figure 7. Effect of fetal perfusate pH on the maternal to fetal clearance of bupivacaine. Steady-state bupivacaine transfer was established with the pH of both circuit at 7.4, after which the fetal pH was changed to 7.2, 7.0, 6.8, and back to 7.4 in 30-min intervals. A significant increase in bupivacaine clearance was seen at each pH level studied. Data expressed as mean plus/minus SEM of 21 clearance observations at each concentration during seven open placental perfusions.