Pre-oxygenation enhances induction with sevoflurane as assessed using bispectral index monitoring

Background: Several methods may enhance the inhalational induction of anesthesia. In this randomized double-blind study, we evaluated the speed of induction of anesthesia with sevoflurane with or without pre-oxygenation. Methods: Fifty-four patients scheduled for hysteroscopy received for 10 min air or 100% oxygen via a facemask followed by ≥ 7% sevoflurane in 100% oxygen. During the first 300 s of sevoflurane administration, bispectral index (BIS) values were recorded every 30 s in all patients. In 14 patients, seven in each group, BIS, endtidal CO₂, tidal volume, respiratory rate, SpO ₂, and heart rate were recorded every minute during the pre-induction period and every 30 s during the first 5 min of sevoflurane administration. Results: The BIS, endtidal CO₂, tidal volume and respiratory rate did not differ between the oxygen or air breathing groups (P = 0.696, P = 0.999, P = 0.388, and P = 0.875, respectively), though the oxygen group exhibited lower tidal volumes by 16-20%. The SpO₂ and heart rates were higher in the oxygen breathing group (P < 0.001 and P = 0.042, respectively). During sevoflurane administration, BIS values were lower in the oxygen group vs. the group breathing air, in particular at 90, 120, 150, 180 and 210 s (P = 0.001, P = 0.001, P = 0.001, P = 0.001 and P = 0.030, respectively). The endtidal CO ₂ and the tidal volumes between the groups did not differ. The two groups differed in the SpO₂ and the heart rates during induction (P = 0.004 and 0.003, respectively). Conclusions: Before sevoflurane administration, breathing 100% oxygen for 10 min enhances induction of anesthesia with sevoflurane.