The effect of sevoflurane on implicit memory: a double-blind, randomised study

Forty-eight gynaecological patients were randomly allocated to three groups (target end-tidal sevoflurane concentration 1.2, 1.5 or 2%), and into subgroups for positive or neutral suggestion. Anaesthesia was induced by inhalation of sevoflurane in oxygen. When the target concentration was achieved, the bispectral index, computed from a bi-frontal electroencephalogram, was noted. One of two eight-word lists was then played to prime implicit memory, followed by a positive or neutral suggestion. After surgery, each patient tried to identify 24 words obscured by background noise. Priming increased the likelihood of identifying words in the 1.2% group only, i.e. there was evidence of implicit memory in this group. There was no evidence of a therapeutic effect of positive suggestion (p = 0.3), but the power of this part of the study was low. The bispectral index did not achieve statistical significance as an indicator of susceptibility to priming.