This study compares the actual standard of care with a new protocol to guide hemodynamic optimization during major abdominal surgery, which is more tailored on patient real needs. During general anesthesia metabolic needs of the body are markedly reduced and increase in CO may not be necessary. In addition, excessive fluid administration has been related to worse post-operative outcomes. We divide patients into three groups: the standard treatment group, the NICE protocol group and the intervention group. In this group we use the v-aCO2/CaO2-CvO2 as marker of tissue ability to increase their oxygen consumption in response to increased O2 delivery, and based on this index the administration of fluid. The principal aim is to optimize functional hemodynamics in order to reduce the fluid balance at the end of the surgery.