1 Department of Anesthesiology and Pain Medicine, Martini General Hospital Groningen, Groningen, The Netherlands, hd.de.boer@mzh.nl Department of Anesthesiology, Intensive Care and Reanimation, AZ Sint Jan Brugge-Oostende Ruddershove 10, Bruges, Belgium Department of Anesthesiology, Leiden University Medical Center, Leiden, The Netherlands.