Background: The use of low-dose continuous infusion of S(+)-ketamine combined with target-controlled intravenous anesthesia with remifentanil and propofol may be related to the control of postoperative pain and of opioid-induced hyperalgesia. The present study aimed to evaluate the efficacy of continuous infusion of S(+)-ketamine given intraoperatively in the control of postoperative pain compared to placebo.

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

Inclusion Criteria:

• 18 Years to 65 Years ASA I and II Accepts healthy volunteers.

Exclusion Criteria:

alcohol or illicit drugs, H2 inhibitors, opioids, or calcium-channel blockers within the last 10 days chronic pain, myocardial ischemia, psychiatric diseases.