1 Department of Procto-Surgery, St Marien Hospital Vechta, Academic Teaching Hospital of the Medical School Hannover, Vechta, Germany. Electronic address: Dietrich.Doll@kkom.de.
2 Department of Anaesthesiology and Pain Therapy, University of Bern, University Hospital Inselspital, Bern, Switzerland. Electronic address: markus.luedi@gmail.com.