Accuracy of Pulse Pressure Variation and of Pleth Variability Index to Predict the Response to a Fluid Challenge

Inclusion Criteria: * patients undergoing major abdominal surgical procedures performed by laparotomy * patients undergoing major urological surgical procedures performed by laparotomy * patients undergoing major gynecological surgical procedures performed by laparotomy * age ≥ 18 years * signed informed consent Exclusion Criteria: * pregnant women * esophageal disease * aortic valve disease * allergy to gelatin * BMI \> 35 * beta blocker treatment, antiarrhythmic treatment, arrhythmia, pace-maker, * presence of an arterio-venous shunt or of any other vascular disease on upper limb