In preparation for surgery, the patients were equipped with central and peripheral venous and arterial catheters. Standard monitoring included continuous recording of electrocardiography; body temperature, heart rate, pulse oxymetry and arterial blood pressure. Central venous pressure, ScvO2 , arterial blood gases, lactate concentration, body temperature, and urine output were recorded hourly. Hemoglobin concentration was measured when deemed necessary by the anesthesiologist. For the purpose of the study, blood gases measured on arterial and central venous samples, arterial lactate and O2ERe (SaO2-ScvO2/SaO2 [SaO2 : arterial oxygen saturation, ScvO2 : central venous saturation]) were recorded after induction of anesthesia (T0), hourly after cutaneous incision (T1a-f), throughout surgery, during the first 6 hours of the postoperative period (T2a-f) and on postoperative day 1.