Fluid therapy optimization in the perioperative period has been considered as major contributor to improve oxygen delivery. A recent, noninvasive approach to estimate fluid requirements in the anesthetized patient with arterial line is the assessment of difference in pulse pressure (dPP). Intraoperative fluid management by dPP is a goal-directed fluid management approach to avoid both hypervolemia and hypovolemia. However, several clinical factors may impede dPP measurements. Surgical manipulations in abdominal procedures may interfere with hemodynamic stability due to obstruction of the caval vein. Physiological considerations make us hypothesize that only intense pressure impedes caval blood flow and thus hemodynamics and dPP. Therefore, the investigators want to assess those changes after standardized application of three different pressure levels (2 N, 5 N, 10 N) on the caval vein.