Epileptiform EEG during sevoflurane mask induction: Effect of delaying theonset of hyperventilation

Background: Hyperventilation during sevoflurane-N2O-O-2 mask induction in a dults is associated with a hyperdynamic circulatory response and epileptifo rm electroencephalogram (EEG). We tested the hypothesis that delaying onset of hyperventilation will prevent severe (periodic) epileptiform EEG and hy perdynamic response. Methods: Thirty patients were randomized to receive either delayed (group D , n=15) or immediate (group I, n=15) onset of hyperventilation during sevof lurane (8% in N2O 50%) mask inhalation induction with single-breath method for unconsciousness. Fifteen patients were allowed to breathe spontaneously for 2 min after loss of consciousness and controlled hyperventilation (ETC O2 <4%) was started thereafter. In 15 patients controlled hyperventilation was started immediately after loss of consciousness. EEG was recorded, and mean arterial pressure (MAP) and heart rate (HR) registered. Results: Epileptiform EEG patterns were seen in 13 patients in group I and in 9 patients in group D (n.s.). Periodic epileptiform discharges (PED) ten ded to occur more often in group I (P=0.07). Heart rate and MAP were higher in group I than in group D from 2 min to 3 min (P<0.05), and both HR and M AP rose significantly from the baseline in group I. In group D, HR but not MAP rose significantly from baseline. Conclusion: Regardless of its timing, hyperventilation at a high sevofluran e concentration produced severe epileptiform EEG with a hyperdynamic respon se. FED tended to occur more often with immediate onset of hyperventilation . (C) Acta Anaesthesiologica Scandinavica 44 (2000).