Abstract
BackgroundAnesthetic administration is increasingly guided by electroencephalography (EEG)-based monitoring, such as the bispectral index (BIS). However, during cardiopulmonary bypass (CPB), factors other than the administered hypnotic agents may influence EEG signals, and their effects on BIS values are unknown.MethodsThis report is a secondary analysis of data from a prospective, controlled interventional study comparing the effect of sevoflurane administration guided by BIS monitoring (group SevoBIS) and constant administration of sevoflurane (group Sevo1.8Vol%) during CPB. Sevoflurane plasma concentration (SPC) was measured using gas chromatography. The relationships of BIS to SPC, CPB pump flow, arterial pressure, hematocrit, temperature, time on CPB, and patient characteristics were analysed.ResultsNo association was observed between BIS values and SPC in group SevoBIS. In group Sevo1.8Vol%, a 40 μg ml-1 increase in SPC, which encompassed the entire range of observed values of the SPC in this analysis, was associated with a decrease of 3.6 (95% confidence interval (CI): 1.1–6.1) in BIS values (p = 0.005). Each increase in CPB time of 10 minutes was associated with an increase in BIS values of 0.25 (95%CI: 0.11–0.39, p<0.001). Path analysis revealed that the BIS values of SevoBIS patients were 5.3 (95%CI: 3.2–7.5) units higher than those of Sevo1.8Vol% patients (p<0.001), which was the strongest effect on BIS values. Path analysis revealed a slope of 0.5 (95%CI: 0.3–0.7) BIS units per 1°C body temperature (p<0.001).ConclusionBIS monitoring is insensitive to clinically relevant changes in SPC in individual patients during CPB.
Highlights
The anesthetic requirement of a patient is nearly impossible to predict due to high betweenpatient and within-patient variabilities of patient needs and is challenging for anesthesiologists during cardiopulmonary bypass (CPB) [1,2,3]
In group Sevo1.8Vol%, a 40 μg ml-1 increase in Sevoflurane plasma concentration (SPC), which encompassed the entire range of observed values of the SPC in this analysis, was associated with a decrease of 3.6 (95% confidence interval (CI): 1.1–6.1) in bispectral index (BIS) values (p = 0.005)
Each increase in CPB time of 10 minutes was associated with an increase in BIS values of 0.25 (95%confidence intervals (CIs): 0.11–0.39, p
Summary
The anesthetic requirement of a patient is nearly impossible to predict due to high betweenpatient and within-patient variabilities of patient needs and is challenging for anesthesiologists during cardiopulmonary bypass (CPB) [1,2,3]. Many clinicians guide anesthetic delivery by monitoring the depth of sedation in cardiac surgery to prevent the under- or overdosing of anesthetics [3,4,5,6]. The most frequently used and validated monitor is the bispectral index (BIS, BIS-Monitor; Covidien, Boulder, CO, USA). Factors other than the hypnotic agents delivered during CPB may influence the EEG signal and interfere with BIS monitoring. Because different causes of changes in BIS values have different therapeutic consequences, it is important for clinicians to understand factors that contribute to the origin of BIS indices during CPB. Anesthetic administration is increasingly guided by electroencephalography (EEG)-based monitoring, such as the bispectral index (BIS). During cardiopulmonary bypass (CPB), factors other than the administered hypnotic agents may influence EEG signals, and their effects on BIS values are unknown
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