1 Department of Anesthesia, Hospital de la Santa Creu I Sant Pau, Barcelona, Spain.
2 Department of Anesthesia, Consorcio Hospital General de Valencia, Valencia, Spain.
3 Department of Anesthesia, Hospital Universitario y Politécnico La Fe de Valencia, Valencia, Spain.
4 Department of Anesthesia, Hospital Ramón y Cajal, Madrid, Spain.
5 Department of Anesthesia and LKSKI of Saint Michael's Hospital, University of Toronto, Toronto, Canada.
6 Iberoamerican Cochrane-Centre-Clinical Epidemiology and Health Service.IIB Sant Pau. CIBERESP, Barcelona, Spain. Electronic address: mmartinezz@santpau.cat.