1. Pain Unit; Department of Anesthesiology and Reanimation; “Virgen de la Salud” University Hospital; Toledo Hospital Complex; Toledo Spain
2. Pain Study and Treatment Unit; “Ramón y Cajal” University Hospital; Madrid Spain
3. Pain Unit; Department of Anesthesiology and Reanimation; Gregorio Marañón University General Hospital; Madrid Spain
4. Puerta de Hierro Majadahonda University Hospital; Madrid Spain
5. Pain Unit; 12 October University Hospital; Madrid Spain
6. Pain Unit; Department of Anesthesiology; Fuenlabrada University Hospital; Madrid Spain
7. Pain Unit; Department of Anesthesiology; “Ruber Internacional” Hospital; Madrid Spain
8. Pain Unit; Department of Anesthesiology and Reanimation; “Infanta Cristina” University Hospital; Parla Madrid Spain
9. Pain Unit; Jiménez-Díaz Foundation University Hospital; Madrid Spain
10. Pain Unit; Madrid-Montepríncipe University Hospital; Madrid Spain
11. Pain Unit; Ciudad Real University Hospital; Ciudad Real Spain
12. Pain Unit; Department of Anesthesiology and Reanimation; “Infanta Sofía” University Hospital; Madrid Spain
13. Pain Unit; Department of Anesthesiology and Reanimation; “San Carlos” Clínical Hospital; Madrid Spain
14. Department of Anesthesiology and Reanimation, Prince of Asturias University; Hospital, Alcalá de Henares; Madrid Spain
15. Pain Unit, Department of Anesthesiology and Reanimation; “Severo Ochoa” University Hospital, Leganés; Madrid Spain
16. Pain Unit, Department of Anesthesiology; idcsalud Group Sur Hospital, Alcorcón; Madrid Spain