1. Department of anesthesia and operative service, Kuopio University Hospital, Kuopio, Finland
2. Department of plastic surgery, Kuopio University Hospital, Kuopio, Finland
3. Operative center, Kuopio University Hospital, Kuopio, Finland
4. Department of neurosurgery, Neurocenter, Kuopio University Hospital, Kuopio, Finland
5. Granlund Consulting, Helsinki, Finland and Finnish Institute of Occupational Health, Kuopio, Finland