1. Department of Anaesthesiology, Hospital Germans Trias i Pujol, Badalona, Spain
2. Department of Medicine, Universitat Internacional de Catalunya, Barcelona, Spain
3. Department of Anaesthesiology, Hospital de Manises, Manises, Spain
4. Department of Anaesthesiology, Consorci Sanitari de Terrassa, Terrassa, Spain
5. Department of Statistics, Universitat Internacional de Catalunya, Barcelona, Spain