Department of Anaesthesiology and Intensive Care Medicine, University Hospital Schleswig-Holstein, Kiel, Germany.
Acta Anaesthesiol Scand. 2010 Feb;54(2):169-75. doi: 10.1111/j.1399-6576.2009.02138.x. Epub 2009 Oct 15.
The bispectral index (BIS) and spectral entropy enable monitoring the depth of anaesthesia. Mild hypothermia has been shown to affect the ability of electroencephalography monitors to reflect the anaesthetic drug effect. The purpose of this study was to investigate the effect of hypothermia during a cardio-pulmonary bypass on the correlation and agreement between the BIS and entropy variables compared with normothermic conditions.
This prospective clinical study included coronary artery bypass grafting patients (n=25) evaluating correlation and agreement (Bland-Altman analysis) between the BIS and both spectral and response entropy during a hypothermic cardio-pulmonary bypass (31-34 degrees C) compared with nomothermic conditions (34-37.5 degrees C). Anaesthesia was maintained with propofol and sufentanil and adjusted clinically, while the anaesthetist was blinded to the monitors.
The BIS and entropy values decreased during cooling (P<0.05), but the decrease was more pronounced for entropy variables compared with BIS (P<0.05). The correlation coefficients (bias+/-SD; percentage error) between the BIS vs. spectral state entropy and response entropy were r(2)=0.56 (1+/-11; 42%) and r(2)=0.58 (-2+/-11; 43%) under normothermic conditions, and r(2)=0.17 (10+/-12; 77%) and r(2)=0.18 (9+/-11; 68%) under hypothermic conditions, respectively. Bias was significantly increased under hypothermic conditions (P<0.001 vs. normothermia).
Acceptable agreement was observed between the BIS and entropy variables under normothermic but not under hypothermic conditions. The BIS and entropy variables may therefore not be interchangeable during a hypothermic cardio-pulmonary bypass.
双频谱指数（BIS）和光谱熵可用于监测麻醉深度。已证明轻度低体温会影响脑电图监测仪反映麻醉药物效应的能力。本研究旨在探讨体外循环期间低温对 BIS 与熵变量之间相关性和一致性的影响，与正常体温条件相比。
这项前瞻性临床研究纳入了 25 例冠状动脉旁路移植术患者，评估了在体外循环低温（31-34°C）与正常体温（34-37.5°C）条件下，BIS 与两种光谱和反应熵之间的相关性和一致性（Bland-Altman 分析）。麻醉维持使用丙泊酚和舒芬太尼，并根据临床情况进行调整，而麻醉师对监测仪则保持盲法。
BIS 和熵值在降温过程中降低（P<0.05），但与 BIS 相比，熵变量的降低更为明显（P<0.05）。在正常体温条件下，BIS 与光谱状态熵和反应熵的相关系数（偏差+/-标准差；误差百分比）分别为 r²=0.56（1+/-11；42%）和 r²=0.58（-2+/-11；43%），在低温条件下，分别为 r²=0.17（10+/-12；77%）和 r²=0.18（9+/-11；68%）。低温条件下偏差显著增加（P<0.001 与正常体温相比）。
在正常体温条件下，BIS 与熵变量之间观察到可接受的一致性，但在低温条件下则不一致。因此，在体外循环期间，BIS 和熵变量可能不能互换使用。
