Effects of High-Inspired Oxygen Fraction During Elective Caesarean Section Under Spinal Anaesthesia on Maternal and Fetal Oxygenation and Lipid Peroxidation

Abstract

Women undergoing cesarean section under regional anesthesia commonly receive supplemental oxygen. A high oxygen fraction may be administered to enhance fetal oxygenation, but this measure also may increase free radical formation and promote lipid peroxidation in both mother and infant. This prospective randomized double-blinded study was intended to clarify the effects of a high-inspired oxygen fraction on these parameters. Forty-four parturients in good general health (ASA I-II) were randomly assigned to breathe either air (containing 21% oxygen) or 60% oxygen during elective cesarean section using the ventimask, a high-flow Venturi-type facemask. Spinal anesthesia was performed using 0.5% hyperbaric bupivacaine and fentanyl. Maternal arterial blood was sampled every 5 minutes, and umbilical cord blood at delivery. Blood gases were measured as well as products of lipid peroxidation including 8-isoprostane, malondialdehyde (MDA), and hydroperoxide (OHP). Maternal and fetal characteristics and operative variables were similar in the air and high-oxygen groups. Oxygen-treated women had higher arterial PO 2 levels at the time of delivery, the mean difference being 16 kPa (P <.001). They also had higher umbilical cord blood venous PO 2 levels than women breathing room air, with a mean difference of 0.8 kPa (P <.04). Both maternal and umbilical blood concentrations of 8-isoprostane, DA, and OHP were greater in women given supplemental oxygen. In both groups, maternal arterial PO 2 correlated positively with umbilical venous levels of 8-isoprostane, OHP, and MDA. Plasma MDA levels increased significantly within 10 minutes of beginning oxygen supplementation. All Apgar scores that exceeded 7 and 9 at 1 and 5 minutes, respectively. Healthy women undergoing cesarean delivery experience a modest increase in fetal oxygenation when breathing a high-inspired oxygen fraction during surgery, but levels of oxygen free radicals increase in both the mother and fetus. The clinical import of the latter observation remains uncertain. In view of the limited benefit, patient discomfort from wearing an oxygen facemask might be taken into account.