Background and Goal of Study: BISxp® Monitoring System readings simultaneously recorded over both sides of the forehead may differ in up to 30% of the measured values(1), and it depends on the type of anaesthesia. Our objective was to compare BIS values of the new BIS VISTA Monitoring System(Aspect Medical Systems, Norwood,MA) simultaneously measured from both sides of the head in the same patient during anaesthesia with 2% sevoflurane in 30% oxygen(Sevo group) and with propofol-70% nitrous oxide(Propo group).
Materials and Methods: This randomized, prospective, comparative, observational study was approved by the local ethics committee. It enrolled 99 patients older than 18 years scheduled for elective surgery.
Patients were excluded if they had a history of stroke, dementia, organic brain disease or carotid bruit. Two BIS Quatro® electrode strips from BIS VISTA® were placed on each side of their forehead. The clocks on both monitors were synchronized before each case to ensure a time difference of < 1second. BIS values generated by both sensors were downloaded for analysis to laptop computers from the induction until emergence from anesthesia.
47 subjects per group were considered necessary to differentiate a bias of 3 point with an alfa and beta error of 0,05.
Bland-Altman tests of agreement and bias were used. Bias differences were compared with the student's t test. Chi square was used to compare proportions.
Results and Discussion: Patients characteristics were similar. There were no bias(0,0,-0,6) between the BIS VISTA monitors in both groups indicating no clinical significant tendency for one side to produce a different measurement than the other.
The dashed line shows the 95% limits of agreement for the left vs right-sided BIS values(fig. 1). These limits with BIS VISTA were smaller than previous(1) and suggest a BISxp® improvement.
Conclusion: With both anaesthetic techiques, bias and limits of agreement were similar.
1) Anesthesiology 2006;104:242-8