Isoflurane 흡입마취 동안 아산화질소가 뇌 엔트로피에 미치는 영향

Abstract

The bispectral index has a limitation to describe the exact depth of anesthesia during ketamine infusion or nitrous oxide inhalation. This study is intended to know the effect of nitrous oxide on cerebral entropy measured by entropy module (M-ENTROPY Module S/5, Datex-Ohmeda division, Instrumentarium Corporation, Helsinki, Finland) during the stable anesthetic maintenance period with isoflurane inhalation. Sixty unpremdicated ASA physical statusⅠ-Ⅱ patients scheduled for elective lower abdominal surgery, age ranging 18-65 years, were randomly allocated into one of the three groups of twenty patients. During the stable anesthetic maintenance period after skin incision, baseline entropy (RE; response entropy, SE; state entropy) were recorded and averaged on a single frontal channel at 0.9% end-tidal isoflurane with medical air in oxygen (FiO₂ = 0.4) for 20 minutes. After this, medical air was used continuously (group C) or replaced by nitrous oxide at 40% (group L) or 60% (group H) with continuous hemodynamic variables and entropy values monitoring. Each of the variables was recorded and analyzed at intervals of 2.5 minutes for 20 minutes. Averaged values (mean ± SD) of RE and SE during experimental period were lower in group H (29.2 ± 12.3, 28.5 ± 11.7) than group L (33.9 ± 7.3, 33.0 ± 7.3) and the averaged values were lower in group L than group C (46.6 ± 14.8, 45.5 ± 14.2). The percent reductions of group H (42.1 ± 14.2, 38.7 ± 16.5) were larger than group L (25.3 ± 15.1, 24.4 ± 14.9) and the percent reductions of group L were larger than group C. The added nitrous oxide during anesthetic maintenance period with isoflurane decrease cerebral entropy and it may be dose-dependant.