 Methods: This is a double-blind randomized controlled trial with 48 patients of both genders aged from 18 to 65 years who underwent videolaparoscopic cholecystectomy. After venipuncture, patients received intravenous parecoxib sodium 40 mg. Target-controlled intravenous anesthesia was induced with propofol and remifentanil associated with rocuronium and adjusted to maintain the bispectral index between 35 and 50. The S-ketamine group SG group received a continuous infusion of S-ketamine at a dose of 0.3mg.kg-1.h-1, while the placebo group PG received a continuous infusion of saline at the same dose. Postoperative analgesia was measured by a verbal numerical scale VNS from 0 to 10 during 12 hours and treated with morphine when VNS score was equal to or higher than 3 at a dose of 0.05 mg.kg-1 when the patient reported pain for the first time and at a dose of 0.025mg.kg-1 on subsequent occasions. Pain scores were recorded in the postoperative care unit PACU and at 4 and 12 hours after the end of the surgery The amount of morphine used during PACU stay, from PACU discharge to 4 hours after surgery, and from 4 to 12 hours after surgery, the overall dose of morphine used, and possible adverse effects were also assessed 