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,