1. Department of Cranio-Maxillo-Facial-Surgery, University Hospital Ulm, 89081 Ulm, Germany
2. Department of Cranio-Maxillo-Facial-Surgery, German Armed Forces Hospital Ulm, 89081 Ulm, Germany
3. Medical Statistics and Biomathematics, Mannheim Medical Faculty of the Heidelberg University, 68167 Mannheim, Germany
4. Department of Anesthesiology and Intensive Care Medicine, Ludwigshafen Hospital, 67063 Ludwigshafen, Germany
5. Department of Anesthesiology and Intensive Care Medicine, University Hospital Ulm, 89081 Ulm, Germany
6. Department of Cranio-Maxillo-Facial-Surgery, Ludwigshafen Hospital, 67063 Ludwigshafen, Germany