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Tuesday, March 08, 2011
It’s alright to let the BIS stay below 40 at least for non-cardiac surgery
If I have any say, a depth of anesthesia monitor is used for the patients I anesthetize. If patients receive a lesser amount of anesthesia, they recover faster, have less postoperative nausea and vomiting and, particularly for patients with cardiovascular compromise, their blood pressure is higher. For some patients, when the depth of anesthesia reading is between 40 and 60, if not paralyzed, they move. Is it safer to paralyze those patients or to deepen their anesthetic? There is some evidence that it might be safer to paralyze these patients. Yet, in a study published this month, characteristics other than depth of anesthesia were associated with increased mortality. The problem with the earlier studies that showed an association between depth of anesthesia and poor outcome was that they did not adequately account for preexisting disease. The editorial that accompanied this month’s study summarized some of the older studies, the controversy that was generated by those studies and the difference between causation and correlation.

In this month’s study, patients were part of the B-Unaware trial. 1,473 non-cardiac surgery patients were studied and their perioperative data was collected. Mean length of follow-up was 3.2 years. Though many characteristics were associated with intermediate-term mortality, there was no association with age–adjusted MAC equivalents or duration of BIS less than 45 or 40.

Is the issue resolved? It definitely is not. Is there something unique to patients who undergo surgery for cancer which puts them specifically at risk, as evidenced by the first paper to show such an association? Certainly, anesthetics may have an effect longer than during the immediate perioperative period; see, for example, two studies(a, b) published this month and also discussed on Page 2 indicating that rats’ exposure to inhalation anesthetics in utero may have an effect on brain development.

More study is needed, but this study was a great start! Tell us what you think.
Posted by J. Lance Lichtor, M.D.
J. Lance Lichor, MD
About the Author

J. Lance Lichtor, M.D
J. Lance Lichtor, M.D. is a professor of anesthesiology and pediatrics at The University of Massachusetts Medical School. He is the web editor and an associate editor for Anesthesiology.

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