 Sample size Estimates of power and minimal group size were obtained by performing a forward looking power analysis based upon the ability to show a significant difference in neurocognitive testing. This is based on our previous study showing a 38 incidence of neurocognitive abnormality in a group consistent with the propofol arm, and aiming for an effect size reduction of 50. For an 80 power to reject the null hypothesis of no significance P0.05 in each group, the sample size is 90 patients in each group. 