Effect of Ultra-low Dose Naloxone on Remifentanil-Induced Hyperalgesia

The purpose of this study is to evaluate whether using ultra-low dose naloxone, an opioid antagonist, has the potential to block remifentanil-induced hyperalgesia and tolerance following surgery. There are 3 study groups: (1) low dose remifentanil (LO, 0.1 micrograms/kg/mL), (2) high dose remifentanil (0.4 mg) combined with placebo (HI, 0.4 micrograms/kg/mL), or (3) high dose remifentanil (0.4 mg) combined with ultra-low dose naloxone (HN, 0.004 micrograms/kg/mL naloxone). The hypothesis of the study is that occurrence of remifentanil-induced hyperalgesia (low score in mechanical pain threshold) in the HN group will be lower than in the HI group.