 Considering the known risk factors for POCD advanced age, major surgery and low level of education, the minimization criterion will be applied to the randomization. Minimization allows to randomize each new patient enrolled in the study in order to minimize the differences between the two allocation arms for the risk factors considered. This means that when a new patient enters the study, the patients own characteristics for the risk factors considered will affect the patients probability to be enrolled in one of the two allocation arms. The minimization criterion allows to reduce unbalancing for known risk factors between the allocation arms of the study. 