Animal studies have shown reliable results for SVV and PVV to discriminate fluid-responder from non-responders if intraabdominal pressure is increased [Jacques D 2011]. In contrast to these findings, van Lavieren and colleagues have shown an inappropriate increase in measured dynamic preload parameters upon opening the abdomen using a non-invasive and uncalibrated system (Nexfin™). The present study thus aims to determine the effects of changes in abdominal pressure on dynamic preload parameters (PPV and SVV) (primary objective) employing an established invasive hemodynamic monitoring tool (Vigileo®, Edwards Lifescience) during open abdominal surgery as well as in minimal invasive surgical procedures using pneumoperitoneum.