BIS monitoring to prevent awareness during general anesthesia

Background: Unexpected awareness is a rare but well-described complication of general anesthesia that has received increased scientific and media atte ntion in the past few years. Transformed electroencephalogram monitors, suc h as the Bispectral Index monitor, have been advocated as tools to prevent unexpected recall. Methods: The authors conducted a power analysis to estimate how many patien ts would be needed in an appropriately powered study to demonstrate the Bis pectral Index monitor reduces awareness, as web as a cost analysis to asses s the cost of using the monitor for this purpose alone. Results: If unexpected recall is rare (1 in 20,000), it will require a larg e study to demonstrate that the monitor reduces awareness (200,000-800,000 patients), and the cost of using it for this purpose alone would be high ($ 400,000 per case prevented). If awareness is common (1 in 100), then the nu mber of patients needed in a study to demonstrate that the monitor works be comes tractable (1,000-4,000 patients), and the cost of using the monitor f or this purpose alone becomes lower ($2,000 per case prevented). Because th ere are reported cases of awareness despite Bispectral Index monitoring, th e authors are certain that the effectiveness of the monitor is less than 10 0%. As the performance of the monitor decreases from 100%, the size of the study needed to demonstrate that it works increases, as does the cost of us ing it to prevent awareness. Conclusion: The contention that Bispectral Index monitoring reduces the ris k of awareness is unproven, and the cost of using it for this indication is currently unknown,