1 German Paediatric Pain Centre, Children's and Adolescents' Hospital, Datteln, Germany.
2 Department of Children's Pain Therapy and Paediatric Palliative Care, Faculty of Health, School of Medicine, Witten/Herdecke University, Witten, Germany.
3 Department of Neuroscience, Physiology and Pharmacology, University College London, London, United Kingdom.
4 Department of Anesthesiology & Pain Medicine, University of Washington School of Medicine, Seattle, WA, United States.
5 Seattle Children's Research Institute, Seattle, WA, United States.