Allart M Venema1, Maarten Uyttenboogaart2, Anthony R Absalom3. 1. Department of Anaesthesiology, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands. Electronic address: a.m.venema@umcg.nl. 2. Department of Neurology, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands; Department of Radiology, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands. 3. Department of Anaesthesiology, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands.