 The hypotheses will be examined in a prospective clinical study by means of tetanic stimulation, tested on presumably 30 elective patients. The study was approved by the Ethics committee of the Medical Board of the City of Hamburg, Germany and informed consent will be obtained from all patients. After induction of deep propofol sedation a laryngeal mask is inserted and sedation is maintained by continuous bispectral index-guided propofol-infusion. Next, remifentanil is increased step-by-step according to the study protocol. 