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Bispectral index and electroencephalographic entropy in patients undergoing aortocoronary bypass grafting

Background and objective: This study was conducted to compare bispectral index, state entropy and response entropy in patients undergoing coronary artery bypass grafting. Methods: In 66 patients, anaesthesia was maintained at two different levels using bispectral index. Doses of sufentanil and midazolam were adjusted to achieve a bispectral index in the range of 45‐55 in 33 patients (BIS 50 group) and 35‐44 in another 33 patients (BIS 40 group). Simultaneously, state entropy and response entropy were recorded. Results: The targeted values of bispectral index were achieved in both groups and the bispectral index values differed significantly during whole anaesthesia. Median response entropy and state entropy fell to 19‐26 during anaesthesia in both groups. Response entropy and state entropy values in the two groups differed significantly only after induction of anaesthesia and did not differ during further anaesthesia. There was no explicit intraoperative recall in both groups. Patients in Group BIS 40 received significantly (P < 0.05) more sufentanil than the BIS 50 group (704 ± 181 &mgr;g vs. 490 ± 107 &mgr;g, respectively) and midazolam (18.5 ± 6.1 mg vs. 15.6 ± 3.8 mg, respectively). After cardiopulmonary bypass, significantly (P < 0.05) more patients in Group BIS40 needed inotropic support with dobutamine (79%) than in the BIS50 group (52%). Time to extubation did not differ between the two groups. Conclusion: In patients undergoing coronary artery bypass grafting, no relationship was found between bispectral index levels and state entropy and response entropy at two different stages of a sufentanil‐midazolam anaesthesia. A bispectral index level of 45‐55 reduced anaesthetic medications used and the need for inotropic support.