Fajardo, M. A.; Lesmes, M. A.; Cardona, L. A. Evaluation of Postoperative Analgesic Effect of Intraoperative Infusions of Tramadol and tramadol/lidocaine/ketamine Compared With morphine/lidocaine/Ketamine in Female Dogs Undergoing Ovariohysterectomy. Arch med vet 2012, 44, 145-153.