Effects of vaginal birth versus caesarean section birth with general anesthesia on blood gases and brain energy metabolism in neonatal rats

Using a rat model, several laboratories have demonstrated long-term effects of Caesarean section (C-section) birth or of global hypoxia during C-secti on birth on a variety of central nervous system. (CNS) parameters. These st udies used C-section delivery from rapidly decapitated dams, to avoid confo unding anesthetic effects, or from darns anesthetized with halothane or eth er under unspecified conditions. Systemic oxygenation or cerebral energy me tabolites in the pups at birth have not been systematically measured in thi s model. To develop and characterize a C-section model with relevance to th e human situation, the present study measured arterial/venous blood gases a nd pH and brain ATP and lactate, a widely accepted measure of CNS hypoxia, in pups born either vaginally, by C-section from decapitated darns, or by C -section from dams anesthetized with nitrous oxide (N2O) and increasing con centrations of isoflurane under well-defined conditions. Immediately after birth, pups born vaginally, by C-section with maternal decapitation, or by C-section with 2.5% isoflurane showed no group differences in systemic pO(2 ) or pH or brain ATP levels, but pCO(2) was elevated in the C-section/2.5% isoflurane group. Pups born by C-section with 3.0, 3.5, or 4.0% isoflurane, showed progressive reductions in blood pO(2) and increases in pCO(2) and b lood pH was reduced with 3.5% isoflurane. Relative to vaginal birth, brain lactate levels were unchanged in pups born by C-section with any concentrat ion (2.5-4.0%) of isoflurane, but reduced in pups born by C-section from de capitated dams. At 1 h (and 4 h) after birth, in both vaginally born contro ls and the 2.5% isoflurane group, brain lactate fell while blood pO(2) and brain ATP remained stable. In the 3.0, 3.5, or 4.0% isoflurane groups, bloo d gases and pH and brain lactate also normalized to control values. In conc lusion, rat neonates show minimal signs of systemic Or CNS hypoxia followin g C-section birth under 2.5% isoflurane with N2O. However, there is a rathe r narrow window of isoflurane concentrations which produces effective mater nal anesthesia without producing respiratory compromise in the neonate. Thu s the results indicate that the level of maternal anesthesia employed is an important factor influencing neonatal systemic and CNS oxygenation during C-section birth. (C) 1999 Academic Press.