PROPOFOL BLOOD-CONCENTRATION AND THE BISPECTRAL INDEX PREDICT SUPPRESSION OF LEARNING DURING PROPOFOL EPIDURAL-ANESTHESIA IN VOLUNTEERS

Propofol is often used for sedation during regional anest hesia. We te sted the hypothesis that propofol blood concentration, the Bispectral Index and the 95% spectral edge frequency predict suppression of learn ing during propofol/epidural anesthesia in volunteers. In addition, we tested the hypothesis that the Bispectral Index is linearly related t o propofol blood concentration. Fourteen healthy, male volunteers were studied on three randomly ordered days: no propofol, target propofol blood concentration 1 mu g/mL, and target propofol blood concentration 2 mu g/mL. Each day, epidural anesthesia (approximate to T11 level) w as induced using 2% 2-chloroprocaine. Propofol was infused by a comput er-controlled pump, and propofol concentration measured in central ven ous blood. We administered a Trivial Pursuit(R)-type question task on all 3 days. The electroencephalogram was monitored continuously (F-p1, F-p2; reference, C-2; ground, mastoid). Propofol caused concentration -related impairment of learning. The propofol blood concentration supp ressing learning by 50% was 0.66 +/- 0.1 mu g/mL. The Bispectral Index value when learning was suppressed by 50% was 91 +/- 1. In contrast, the 95% spectral edge frequency did not correlate well with learning. The Bispectral Index decreased linearly as propofol blood concentratio n increased (Bispectral Index = -7.4 .[propofol] + 90; r(2) = 0.47, n = 278). There was no significant correlation between the 95% spectral edge frequency and propofol concentration. In order to suppress learni ng, propofol blood concentrations reported to produce amnesia may be t argeted. Alternatively, the Bispectral Index may be used to predict an esthetic effect during propofol sedation.