The Nexfin monitoring device relies on noninvasive pressure measurement using a finger-cuff manometer, combined with NIRS technology. The accuracy of the signal is dependent on the degree of vascular unloading, which takes an period before optimal unloading is reached. The evolution of the degree of inaccuracy caused by inclomplete unloading is quantified, and the absolute and relative inaccuracy of the nexfin as a function of the time is determined compared to the invasive blood pressure (IBP).

Secondly, the accuracy of the Nexfin to predict the IBP is compared with the accuracy of noninvasive blood pressure to predict the IBP.

In patients under stable anesthesia conditions, who have IBP and NIBP monitoring, the Nexfin will additionaly be connected. All data will be recorded for at least 30 minutes. NIBP will be measured every 5 minutes The evolution of the NIBP, IBP and Nexfin-derived blood pressure will be analysed to determine the evolution of inaccuracy due to incomplete vascular unloading and to determine the accuracy of Nexfin compared with NIBP to determine IBP.

Inclusion Criteria:

• Patients that are accepted for surgery

Exclusion Criteria:

• Patients unable or unwilling to provide consent.

120 Adult patients, that are having a routine surgical procedure.