Purpose: To show that the bispectral index (BIS) is not only a monitor of the depth of anesthesia but that acute decreases of the index may be related to severe cerebral ischemia.
Clinical features: Several clinical observations suggest that an unexplained fall of the BIS may be the result of cerebral ischemia. Somatosensory evoked potentials decreased in parallel to the decrease in BIS during carotid clamping in a 58-yr-old patient undergoing carotid endarterectomy. In a 62-yr-old patient undergoing resection of an aortic aneurysm, the BIS decreased from 40-50% to 8% as the cardiac index and central venous O(2) saturation decreased. The BIS returned to normal values when the low cardiac output was corrected pharmacologically.
Conclusion: While the BIS is a well accepted monitor of the depth of anesthesia, several factors, unrelated to anesthesia, can modify the index. Thus, to adjust the level of anesthesia based solely on the BIS could be inappropriate. While the sensitivity and specificity of the BIS for this indication have not been determined, we suggest that the BIS may be useful to detect severe cerebral ischemia.