PMID: 36822Jul 1, 1979

Effects of changes in maternal--fetal pH on the transplacental equilibrium of bupivacaine

R L KennedyT Turner


Increases in the maternal-fetal pH gradient that may occur during labor and delivery may increase the fetal concentration of local anesthetics. The authors evaluated effects of pH changes on the transplacental concentration equilibrium of bupivacaine. They increased the maternal-fetal pH gradient in each of six pregnant ewes from a control value of 0.15 to 0.54 by hyperventilating the lungs of the ewe and infusing lactic acid into her fetus. After infusion of bupivacaine, 0.15 mg/kg, intravenously into the mother, the drug rapidly appeared in fetal blood, with values significantly increased over control values at 1 and 5 min. The fetal/maternal (f/m) ratios were increased significantly at 5, 15, and 30 min. The f/m ratios had stabilized by 15 min in both control and experimental states, suggesting that equilibrium had been achieved. The consistently low f/m ratios are explained by the presumed similarity of the ovine maternal and fetal protein binding rates to those of man. It is concluded that the maternal and fetal pH values are major factors in the determination of the f/m ratios.


Jan 1, 1983·Pharmacology & Therapeutics·G W Mihaly, D Morgan
Jan 1, 1986·Journal of Perinatal Medicine·W Müller-HolveP Nagler
Jul 1, 1993·International Journal of Obstetric Anesthesia·R J CarsonF Reynolds
Jul 1, 1985·British Journal of Obstetrics and Gynaecology·A Hamshaw-Thomas, F Reynolds
Dec 1, 1980·Acta Anaesthesiologica Scandinavica·C CarlssonA Hanson
Nov 1, 1985·Clinical Allergy·D Vervloet

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