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 CO 2 , 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 CO 2 , 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 SpO 2 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 SpO 2 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.