1. Department of General Surgery, Burgos University Hospital, Avenida Islas Baleares 3, 09006 Burgos, Spain
2. Department of General Surgery, University Hospital “Marqués de Valdecilla”, Avenida Valdecilla, s/n, 39008 Santander, Spain
3. Department of Epidemiology, Preventive Medicine and Public Health, School of Medicine, University of Cantabria, Avenida Herrera Oria, s/n, 39011 Santander, Spain