aDepartment of Anesthesiology, Center of Anesthesiology and Intensive Care Medicine, University Medical Center Hamburg-Eppendorf, Hamburg, Germany

bOutcomes Research Consortium, Cleveland, Ohio, USA

Correspondence to Kristen K. Thomsen, Department of Anesthesiology, Center of Anesthesiology and Intensive Care Medicine, University Medical Center Hamburg-Eppendorf, Martinistrasse 52, 20246 Hamburg, Germany. Tel: +49 40 7410 52415; e-mail: [email protected]