[1] Univ Hosp Ulm, Dept Anaesthesiol & Intens Care Med, Pain Therapy Unit, Albert Einstein Allee 23, D-89075 Ulm, Germany
[2] Med Ctr Univ Freiburg, Interdisciplinary Pain Ctr, Breisacher Str 117, D-79016 Freiburg, Germany
[3] Univ Bonn, Cura Hosp, Weaning Ctr.GFO Clin Bonn, Ctr Pain Med,Dept Anaesthesiol Intens Med Pain & P, Schuelgenstr 15, D-53604 Bad Honnef, Germany
[4] Univ Med Ctr Regensburg, Dept Anaesthesiol, Regensburg, Germany
[5] Univ Bern, Bern Univ Hosp, Dept Anaesthesiol & Pain Med, Inselspital, CH-3010 Bern, Switzerland