The purpose of the study is to determine if the new Composite Variability Index (CVI) is capable of detecting changing effect compartment concentrations of remifentanil. In addition, it is planed to detect if the change in CVI in response to a standardized painful stimulus is dose-dependent.

On the day of surgery, patients receive anesthesia by propofol infusion. As soon as the patient is unresponsive und unconscious (BIS 40-60) and a steady state is achieved, a standardized painful stimulus is applied by electrical stimulation of the ulnar nerve (tetanic stimulation [70 mA], 30 seconds, 50 Hz) in group 1. Thereafter remifentanil is infused to an effect compartment concentration target of 1 ng/ml. The standardized stimulus is applied again as the remifentanil target is reached. This procedure is repeated with remifentanil targets of 2 ng/ml and 3ng/ml. In group 2 remifentanil is targeted to effect compartment concentrations of 3 ng/ml followed by 2,1, and 0 ng/ml.

After measuring the effect of the last painful stimulus the patient is intubated for surgery. Throughout the study the Composite Variability Index and standard monitoring is recorded.

Inclusion Criteria:

• Patients undergoing surgical procedure in general anesthesia

Exclusion Criteria:

• Pregnancy, drug abuse, cardiac arrhythmia, obesity