Background: The dynamic preload variables (pulse pressure variation (PPV), stroke volume variation (SVV) and systolic pressure variation (SPV)) are good predictors of fluid responsiveness. To give a good interpretation of the results the patient has to be mechanically ventilated with a tidal volume > 7-8 ml kg-1, must have a sinus rhythm and no open thorax. The Nexfin® is a new device that can measure and determine the blood pressure and other hemodynamic parameters, such as stroke volume, cardiac output, pulse pressure variation and stroke volume variation in a non-invasive way. There has hardly been research to the PPV and SVV measured by the Nexfin® and their ability to predict fluid responsiveness, like PPV and SVV do if they are measured by other devices. Objective: The aim of the present study was to determine if the PPV and SVV, measured by the Nexfin®, were able to predict fluid responsiveness in mechanically ventilated patients under general anesthesia. Method: In this observational prospective study, 91 patients were included who were mechanical ventilated with a tidal volume >8 ml kg-1, needed Voluven® on indication of the anesthetist, had a sinus rhythm, were older than 18 years, had no open thorax and underwent surgery under general anesthesia. Blood pressure (MAP), heart rate (HR), stroke volume index (SVI), cardiac index (CI), pulse pressure variation (PPV) and stroke volume variation (SVV) were continuously recorded by the Nexfin®, from at least five minutes before fluid administration untill at least five minutes after fluid administration. Further analysis was undertaken with the median value over a minute before administration of Voluven® and the median value over a minute after fluid administration. An increase of 15% of SVI was considered clinically significant. Results: 78 patients were included in the analysis. Both SVI and CI correlated significantly with PPV and SVV. The areas under the receiver operating curve (AUROC’s) of PPV and SVV were 0.815 and 0.790 respectively. The ideal cut-off values found, were 16.50% for PPV and 15.75% for SVV. The corresponding specificity found for PPV and SVV were respectively 93.8% and 97.9%. The corresponding sensitivity found for PPV and SVV were 70% and 60% respectively. Conclusion: The PPV and SVV, as measured by the Nexfin®, were able to predict fluid responsiveness. The results though, were less convincing than the PPV and SVV measured in previous studies with other equipment. Using threshold values from the present study, the specificity was much higher than the sensitivity.