In the last years, there is a growing interest in the improvement of prognosis and shortening of hospital length of stay in high-risk surgical patients. Several evidence-based protocols ("fast-track" surgery) have been developed and implemented in some hospitals for this purpose. Cardiovascular optimization through the so-called "goal-directed therapy" (GDT) is a key element in these protocols. Previous studies in the literature use invasive monitors to assess hemodynamics. The NICOM ™ is a non-invasive monitor validated in several clinical scenarios. The aim of the present randomized, international, multi-center, open-label clinical trial is to use a GDT protocol (including colloid boluses and vasoactive drug infusion) based on data obtained from the NICOM™ device (cardiac index and mean arterial pressure) to test the hypothesis that GDT is superior to standard practice in terms of reduction in the incidence of perioperative complications and length of hospital stay in high-risk major abdominal surgery patients (requiring ICU surveillance for, at least, 24 hours). As secondary objectives, time to first flatus, wound infection, anastomotic leaks and mortality will be analysed. All patients will be followed from the day of surgery up to hospital discharge (determined by a specialist surgeon not involved in the study) or death.