Continuous and Discontinuous Determination of Propofol Concentration in Breathing Gas

This study should compare the propofol concentration in breathing gas and in plasma (before and) after lung passage. Propofol concentrations in breathing gas are continuously measured by a sensor. For comparison a discontinuous method is used. Neurophysiologic parameters for determination of depth of anesthesia are compared to the continuous measured propofol concentration in breathing gas. Study hypothesis: continuous measured propofol concentration in breathing gas correlates to propofol concentration in plasma and depth of anaesthesia.