The critical manipulable variables of hemispheric low flow during carotid surgery.
A significant EEG change, 40% power attentuation in anesthetic-induced fast activity, was documented with a tracing record, compressed spectral analysis, and PSA-1 in this series of 195 patients. Interpretation of the change was simplified by the use of the compressed spectral analysis or PSA-1. Quantification of the change was aided by use of the PSA-1, and the graphic output form of this instrument minimized user error. Also, it provided the needed information to those members of the operative team not skilled in EEG interpretation. No immediate postoperative deficits were missed by the monitoring technique. There were no postoperative deficits upon awakening in the 138 patients without processed EEG change. Shunt placement, depth of anesthesia, and intraoperative blood pressure levels were accurately guided throughout the operative procedure by these monitoring techniques. Accurate documentation of an acute significant change permits prompt treatment for restoration of necessary collateral flow. The monitoring technique described continuously provides information for efficacy of treatment. Attention to blood pressure level, which seems to passively determine cerebral collateral flow during clamping, was a very important clinically manipulable variable. Manipulation of this variable with processed EEG control may prove efficacious not only in patients undergoing carotid procedures but in nonsurgical cases of acute carotid occlusion or middle cerebral stem occlusion. Manipulation of identifiable critical variables has a positive impact on the clinical outcome when continuous monitoring is employed. The detection of hemispheric low flow in 34 patients during the preclamp, clamp, and postclamp periods suggests that shunting will not prevent all low flow deficits. Finally, perfection of surgical therapy for stroke prevention necessitates detection and treatment of hemispheric low flow.