This is a prospective study conducted between March 2013 and November 2014 at Hospital Universitario Puerta de Hierro-Majadahonda, in Madrid, Spain, with the previous approval by the institutional clinical research ethics committee. A total of 91 subjects who underwent general, gastrointestinal, orthopedic, urology and neurological surgery were randomly selected and provided written informed consent before any study-related procedures were performed.