The effects of nitrous oxide on the auditory evoked potential index during sevoflurane anaesthesia

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Abstract
Summary We have studied the effects of nitrous oxide on the auditory evoked response index (AAI™‐index) derived from the A‐line monitoring device during sevoflurane anaesthesia in 21 patients undergoing minor ambulatory surgery. During sevoflurane anaesthesia with an AAI™‐index < 30, the addition or withdrawal of nitrous oxide in a concentration of 66% end tidal did not show any linear dose dependent change in AAI™‐index. However, comparing nitrous oxide > 40% to nitrous oxide < 10% end tidal concentration the AAI™‐index did decrease, p < 0.05. The AAI™‐index is either non‐linear at deeper anaesthetic levels or is insensitive to the anaesthetic effects of nitrous oxide in terms of MAC‐multiples.