Preventive effect of postoperative nausea and vomiting will be correlated with the dose of intraoperative acetaminophen : a randomized clinical trial about patients without pain

INTERVENTION: intraoperative intravenous acetaminophen 15mg/kg intraoperative intravenous acetaminophen 7.5mg/kg intraoperative intravenous saline 100ml CONDITION: Orthopedic upper limb or leg disorders PRIMARY OUTCOME: Postoperative nausea and vomiting evaluation performed by numerical rating scale(NRS) after 30 minutes,2 hours,6 hours,24 hours postoperatively. INCLUSION CRITERIA: patients of ASA 1‐2 who are scheduled to undergo general‐epidural anesthesia or general‐conduction anesthesia in an operation of orthopedic upper limb or leg