aDepartment of Anesthesiology, Pain Medicine and Procedural Sedation and Analgesia, Martini General Hospital Groningen, Groningen, the Netherlands

bDepartment of Anesthesiology and Critical Care Medicine, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA

cDepartment of Anaesthesia and Pain Medicine, Royal Surrey County Hospital, Guildford, UK

Correspondence to Hans D. de Boer, MD, PhD, Department of Anesthesiology, Pain Medicine and Procedural Sedation and Analgesia, Martini General Hospital Groningen, van Swietenplein 1, 9728NT Groningen, the Netherlands. Tel: +31 5247352; e-mail: [email protected]