The main objective of this study is to demonstrate that the LIR (Learning Intravenous Resuscitator) Closed-Loop Fluid Administration System (hereafter the "LIR system"), a new device for the automated administration of intravenous fluids during major abominal surgery and which allows the reinjection of 250 ml of saline filling (crystalloid or colloid), maintains blood volume at values that are acceptable by the "gold standard", i.e. the anesthetist in charge of the patient.