Correlation and agreement between the bispectral index vs. state entropy during hypothermic cardio-pulmonary bypass.
BACKGROUND
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.


METHODS
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.


RESULTS
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).


CONCLUSIONS
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.
Department of Anaesthesiology and Intensive Care Medicine, University Hospital Schleswig-Holstein, Kiel, Germany. meybohm@anaesthesie.uni-kiel.de
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P
Meybohm
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Gruenewald
J
J
Höcker
J
J
Renner
J-T
JT
Graesner
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C
Ilies
J
J
Scholz
B
B
Bein
D000368:Aged; D018681:Anesthetics, General / Q000008:administration & dosage; D018686:Anesthetics, Intravenous / Q000008:administration & dosage; D001785:Blood Gas Monitoring, Transcutaneous; D001794:Blood Pressure / Q000502:physiology; D001831:Body Temperature / Q000502:physiology; D002315:Cardiopulmonary Bypass; D001026:Coronary Artery Bypass; D004562:Electrocardiography; D004569:Electroencephalography / Q000706:statistics & numerical data*; D004576:Electromyography; D019277:Entropy; D005260:Female; D006801:Humans; D007036:Hypothermia, Induced; D007385:Intermittent Positive-Pressure Ventilation; D008297:Male; D016343:Monitoring, Intraoperative / Q000706:statistics & numerical data*; D010092:Oximetry; D015742:Propofol / Q000008:administration & dosage; D011446:Prospective Studies; D016037:Single-Blind Method; D017409:Sufentanil / Q000008:administration & dosage
D018681:Anesthetics, General; D018686:Anesthetics, Intravenous; D017409:Sufentanil; D015742:Propofol