The human brain constitutes only 2% of the total weight of the adult, however, given the large consumption of oxygen it demands, it requires more energy than any other organ to carry out its functions.The relationship between cerebral blood Flow (CBF) and cerebral metabolic rate (CMR) is complex and is controlled by several mechanisms that respond both to local intrinsic metabolic needs, as well as external factors such as blood pressure, carbon dioxide (CO 2 ) concentration, O 2 tension, changes in temperature, neural factors, and medications.This article aims to present with precision the aspects related CBF and CMR, explain the factors that influence their regulation, illustrate the effects exerted by some of the main drugs in anesthesia and the impact on the relationship of CMR and CBF.