Randomized,double-blind comparison of different inspired oxygen fractions during general anaesthesia for Caesarean section

Background. The optimal inspired oxygen fraction FI_O2 for fetaloxygenation during general anaesthesia for Caesarean sectionis not known. Methods. We randomized patients having elective Caesarean sectionto receive one of the following: FI_O2 0.3, FI_N2O 0.7 and end-tidalsevoflurane 0.6% (Group 30, n=20); FI_O2 0.5, FI_N2O 0.5 and end-tidalsevoflurane 1.0% (Group 50, n=20), or FI_O2 1.0 and end-tidalsevoflurane 2.0% (Group 100, n=20) until delivery. Neonataloutcome was compared biochemically and clinically. Results. At delivery, for umbilical venous blood, mean PO₂ wasgreater in Group 100 (7.6 (SD 3.7) kPa) compared with both Group30 (4.0 (1.1) kPa, P<0.0001) and Group 50 (4.7 (0.9) kPa,P=0.002) and oxygen content was greater in Group 100 (17.2 (1.6)ml dl^–1) compared with both Group 30 (12.8 (3.6) ml dl^–1,P=0.0001) and Group 50 (13.8 (2.6) ml dl^–1, P=0.0001).For umbilical arterial blood, PO₂ was greater in Group 100 (3.2(0.4) kPa) compared with Group 30 (2.4 (0.7) kPa, P=0.003),and in Group 50 (2.9 (0.8) kPa) compared with Group 30 (2.4(0.7) kPa, P=0.04); oxygen content was greater in Group 100(10.8 (3.5) ml dl^–1) than in Group 30 (7.0 (3.0) ml dl^–1,P<0.01). Apgar scores, neonatal neurologic and adaptive capacityscores, and maternal arterial plasma concentrations of epinephrineand norepinephrine before induction and at delivery were similaramong groups. No patient reported intraoperative awareness. Conclusions. Use of FI_O2 1.0 during general anaesthesia forelective Caesarean section increased fetal oxygenation. Br J Anaesth 2002; 89: 556–61