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Awake on the table: 'Index' falls short

St. Louis — Bispectral index, a brain-activity monitoring system that has gained favor as a way to detect an anesthetized patient’s awareness during surgery, may be no more effective in doing so than the tried-and-true method of measuring anesthetic gases in a patient’s breath, ABC News reports.

In an international randomized trial led by Michael S. Avidan, M.B., B.Ch., professor of anesthesiology at Washington University School of Medicine, there were fewer cases of “unintended intraoperative awareness” among patients monitored by measuring gas concentrations than among those whose brain activity was measured by the bispectral index method.

The study found that 27 of 5,713 patients — all considered at high risk for intraoperative awareness — had either definite or possible awareness during their surgery, based on follow-up interviews. The patients had been randomly assigned to be monitored either by the bispectral index — the BIS group — or the standard method, known as end tidal anesthetic-agent concentration (ETAC). None of the patients reported feeling pain.

Investigators cautioned that the results may not apply to all surgical patients, since those in the study were at high risk for intraoperative awareness and were sedated with gases. Results might differ for patients at lower risk or sedated intravenously, they noted.

The study appears in the Aug. 18 issue of the New England Journal of Medicine.

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