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

Background. The optimal inspired oxygen fraction FIO2 for fetal oxygenation during general anaesthesia for Caesarean section is not known. Methods. We randomized patients having elective Caesarean section to receive one of the following: FIO2 0.3, FIN2O 0.7 and end-tidal sevoflurane 0.6% (Group 30, n=20); FIO2 0.5, FIN2O 0.5 and end-tidal sevoflurane 1.0% (Group 50, n=20), or FIO2 1.0 and end-tidal sevoflurane 2.0% (Group 100, n=20) until delivery. Neonatal outcome was compared biochemically and clinically. Results. At delivery, for umbilical venous blood, mean PO2 was greater in Group 100 (7.6 (SD 3.7) kPa) compared with both Group 30 (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 capacity scores, and maternal arterial plasma concentrations of epinephrine and norepinephrine before induction and at delivery were similar among groups. No patient reported intraoperative awareness. Conclusions. Use of FIO2 1.0 during general anaesthesia for elective Caesarean section increased fetal oxygenation.