Assessment of xenon-induced depth of hypnosis according to Kugler’s scale in elderly and senile patients undergoing knee replacement surgery: a prospective open-label cohort study

Abstract

INTRODUCTION. Anesthesia with xenon is characterized by stable hemodynamic parameters, cardio- and neuroprotection preferable in elderly. Assessment of the depth of hypnosis remains challenging. The Kugler classification based on electroencephalogram has been suggested for such assessment. OBJECTIVES. To assess the feasibility of Kugler scale for objective assessment of the depth of hypnosis induced by xenon alone or in combination with narcotics and regional anesthesia during knee arthroplasty in elderly. MATERIALS AND METHODS. The study included 57 patients divided into 2 groups. In group 1, general anesthesia with xenon was performed, fentanyl and femoral nerve block were used for pain control. In group 2, xenon anesthesia was performed in combination with femoral and sciatic nerve block. The depth of hypnosis was monitored using EEG and matched with the Kugler scale. Also, the bispectral index (BIS) was recorded. RESULTS. At xenon concentration of 40 %, the depth of hypnosis reached D2 stage in group 1 and D1 in group 2 patients, while at 55 % and above it was D2 in both groups. Fentanyl increased the δ-rhythm by 19.08 %, which corresponded to reduction in the effective xenon concentration by 20 %. A correlation between δ-rhythm decrease and BIS was seen in groups 1 (r = –0.78; R2 = 60 %) and 2 (r = –0.61; R2 = 37 %). The differences could be related to the use of fentanyl in group 1. The intergroup difference between the reduction of BIS was not significant. CONCLUSIONS. In elderly patients undergoing knee arthroplasty under combined anesthesia, stage D2 according to Kugler scale (proportion of δ-rhythm more than 50 %) is achieved at xenon concentration of 55 % without narcotics and at concentration of 40 % with fentanyl. The diminished correlation between δ-rhythm and BIS in group 2 and no difference in decrease of BIS suggests that BIS is less accurate for determining the depth of hypnosis during xenon monoanesthesia.