High-dose remifentanil infused intraoperative ironically results in postoperative hyperalgesia. Ultra-low dose nalxone is demonstrated to prevent these opioid-induced hyperalgesia in animal model. In this clinical trial in patients undergoing general anesthesia with remifentanil, we evaluate the effects of ultra-low-dose naloxone on remifentanil-induced hyperalgesia

We enrolled adult patients undergoing thyroidectomy under general anesthesia with desflurane and remifentanil. Remifentanil was administered via target-controlled infusion and anesthetic depth was maintained keeping the BIS between 40 and 60. Patients were randomized into one of three groups depending on intraoperative doses of remifentanil and naloxone: effect-site concentrations of remifentanil 1 ng/ml (control group), 4 ng/ml (remifentanil group), and 4 ng/ml combined with infusion rate 0.8 ng/kg/min of naloxone (remifentanil and naloxone group). Postoperative mechanical pain thresholds, pain intensity, and analgesic consumption were examined during 48 h of postoperative period. The primary outcome was mechanical pain threshold measured on the peri-incisional area 24 h after surgery.

Inclusion Criteria:

• patients who are scheduled to undergo elective thyroidectomy

Exclusion Criteria:

• consent refusal, obesity, pregnancy, hx. of thyroid surgery, neurological disorders, psychiatric disorders, hx. of drug abuse or chronic use of opioids or sedative drugs, intake of any analgesic drug within 12h before surgery.