1. Department of Neurosurgery, Cantonal Hospital of Aarau, 5001 Aarau, Switzerland
2. Faculty of Medicine, University of Bern, 3012 Bern, Switzerland
3. Department of Anaesthesiology, Rescue- and Pain Medicine, Cantonal Hospital of St. Gallen, 9007 St. Gallen, Switzerland
4. Department of Anaesthesiology and Pain Medicine, Inselspital, Bern University Hospital, University of Bern, 3010 Bern, Switzerland