Is Depth of Anesthesia, as Assessed by the Bispectral Index, Related to Postoperative Cognitive Dysfunction and Recovery?

In Brief We randomized 74 patients to either a lower Bispectral Index (BIS) regimen (median BIS, 38.9) or a higher BIS regimen (mean BIS, 50.7) during the surgical procedure. Preoperatively and 4–6 wk after surgery, the patients’ cognitive status was assessed with a cognitive test battery consisting of processing speed index, working memory index, and verbal memory index. Processing speed index was 113.7 ± 1.5 (mean ± se) in the lower BIS group versus 107.9 ± 1.4 in the higher BIS group (P = 0.006). No difference was observed in the other two test battery components. Somewhat deeper levels of anesthesia were therefore associated with better cognitive function 4–6 wk postoperatively, particularly with respect to the ability to process information. IMPLICATIONS: Elderly patients were randomized to lighter or deeper levels of anesthesia, as measured by Bispectral Index. The deeper anesthetic group had better cognitive function 4-6 weeks postoperatively.