Effects of different inspired oxygen fractions on lipid peroxidation during general anaesthesia for elective...

During general anaesthesia (GA) for Caesarean section (CS), fetal oxygenation is increased by administering an inspired oxygen fraction (Fi(o(2))) of 1.0. However, it is unclear whether such high Fi(o(2)) will increase oxygen free radical activity.

We randomized 39 ASA I-II parturients undergoing elective CS under GA to receive 30% (Gp 30), 50% (Gp 50), or 100% (Gp 100) oxygen with nitrous oxide and sevoflurane adjusted to provide equivalent minimum alveolar concentration. Baseline maternal arterial blood before preoxygenation and maternal arterial, umbilical arterial and venous blood at delivery were sampled for assays of the by-product of lipid peroxidation, isoprostane, and for measurement of blood gases and oxygen content.

Maternal and umbilical isoprostane concentrations were similar among the three groups at delivery, despite significantly increased maternal and fetal oxygenation in Gp 100. However, paired comparisons of maternal delivery vs baseline concentration of isoprostane showed an increase at delivery for all groups [Gp 30: mean 342 (sd 210) vs 154 (65) pg ml(-1), P=0.016; Gp 50: 284 (129) vs 156 (79) pg ml(-1), P=0.009; Gp 100: 332 (126) vs 158 (68) pg ml(-1), P<0.001]. The magnitude of increase was similar in all three groups and independent of the Fi(o(2)) or duration after induction.

GA for CS is associated with a marked increase in free radical activity in the mother and baby. The mechanism is unclear but it is independent of the inspired oxygen in the anaesthetic mixture. Therefore, when 100% oxygen is administered with sevoflurane for GA, fetal oxygenation can be increased, without inducing an increase in lipid peroxidation.