The response of bispectral index to laryngoscopy, comparison between hemispheres in patients with a brain tumour versus a healthy control group

Background and Goal of Study: Electroencephalogram during anaesthesia may be affected by brain tumour.(1) We studied whether patients with a brain tumour have different BIS responses after laryngoscopy (LAR). We compared tumour patients with healthy control patients. Materials and Methods: After EC approval, 40 ASA 1 or 2 patients (control) and 41 intracranial tumour patients(tumour) received standardized anaesthesia while measuring bilateral BIS (BIS VISTAXP4 with bilateral sensor).(Covidien, Dublin, Ireland) Remifentanil was randomized to 3 or 5ng/ml effect‐site concentration (Minto) and maintained throughout the study. Propofol effect‐site concentration(CePROP)(Schnider) was set at 2 μg/ml and increased with incremental steps of 0.5 μg/ml until loss of consciousness was observed. After 3 minutes, laryngoscopy was performed and BIS was monitored during one minute. The median BIS of 1 minute before LAR is subtracted from the median BIS one minute after LAR to obtain delta BIS for each hemisphere. We tested if delta BIS is significantly different between hemispheres in control, between healthy and diseased hemispheres in tumour and between ipsilateral control and tumour hemispheres. Statistical significance was set at p< 0.05. Results and Discussion: No demographic differences were present except for age.(table 1) Delta BIS is not statistically different, neither between hemispheres in control, nor between healthy and diseased hemispheres in tumour groups.(table 2) No significant difference was found in delta BIS between ipsilateral control and pathological hemispheres. Conclusion(s): Bilateral BIS does not provide additional information on responsiveness to a standardized stimulus. We could not observe major differences in bilateral BIS response between control and brain tumour patients. Unilateral BIS monitoring seems to be equally informative in healthy and brain tumour patients compared to bilateral monitoring

General Purpose Pharmacokinetic-Pharmacodynamic Models for Target-Controlled Infusion of Anaesthetic Drugs:A Narrative Review

Target controlled infusion (TCI) is a clinically-available and widely-used computer-controlled method of drug administration, adjusting the drug titration towards user selected plasma- or effect-site concentrations, calculated according to pharmacokinetic-pharmacodynamic (PKPD) models. Although this technology is clinically available for several anaesthetic drugs, the contemporary commercialised PKPD models suffer from multiple limitations. First, PKPD models for anaesthetic drugs are developed using deliberately selected patient populations, often excluding the more challenging populations, such as children, obese or elderly patients, of whom the body composition or elimination mechanisms may be structurally different compared to the lean adult patient population. Separate PKPD models have been developed for some of these subcategories, but the availability of multiple PKPD models for a single drug increases the risk for invalid model selection by the user. Second, some models are restricted to the prediction of plasma-concentration without enabling effect-site controlled TCI or they identify the effect-site equilibration rate constant using methods other than PKPD modelling. Advances in computing and the emergence of globally collected databases has allowed the development of new "general purpose" PKPD models. These take on the challenging task of identifying the relationships between patient covariates (age, weight, sex, etc) and the volumes and clearances of multi-compartmental pharmacokinetic models applicable across broad populations from neonates to the elderly, from the underweight to the obese. These models address the issues of allometric scaling of body weight and size, body composition, sex differences, changes with advanced age, and for young children, changes with maturation and growth. General purpose models for propofol, remifentanil and dexmedetomidine have appeared and these greatly reduce the risk of invalid model selection. In this narrative review, we discuss the development, characteristics and validation of several described general purpose PKPD models for anaesthetic drugs