1. Department of Intensive and Intermediate Care, Medical Faculty, RWTH Aachen University, 52074 Aachen, Germany
2. Department of Neurosurgery, Medical Faculty, RWTH Aachen University, 52074 Aachen, Germany
3. Department of Neurosurgery, Cantonal Hospital Aarau, 5001 Aarau, Switzerland
4. Institute of Medical Statistics, RWTH Aachen University, 52074 Aachen, Germany