LAUSR

Background The addition of intrathecal morphine (ITM) to neuraxial anesthesia during total knee arthroplasty (TKA) to achieve postoperative analgesia can elicit opioid-related side effects. The other methods of pain alleviation and side effect reduction, including multimodal analgesia, are challenging. This study aimed to determine the efficacy of various ITM dosages for primary unilateral TKA with periarticular injection (PI). Methods This randomized double-blind controlled trial was conducted at Vajira Hospital between April 2018 and March 2019. Patients undergoing TKA were randomized into 3 groups: no ITM (M0), ITM 0.1 mg (M1), and ITM 0.2 mg (M2). All patients received PI. Postoperative pain scores, side effects of ITM, and orthopedic outcomes were compared. Results The trial enrolled 102 patients: M0 (n = 32), M1 (n = 35), and M2 (n = 35). The postoperative pain scores and rescue analgesic consumption of groups M1 and M2 did not differ significantly within the first 24 hours and were significantly lower than those in group M0. Nausea and vomiting were observed more frequently 4 hours postoperatively in M2 than in groups M1 and M0 (77%, 51%, and 6%, respectively; P < .05), which required second-line antiemetic administration (29%, 9%, and 13%, respectively; P = .09). Conclusion Postoperative pain control achieved with PI combined with ITM 0.1 mg after primary unilateral TKA was comparable to that achieved with ITM 0.2 mg. PI without ITM resulted in higher pain scores and rescue analgesic consumption. The frequency and severity of nausea and vomiting 4 hours postoperatively were also lower in patients administered 0.1 mg of ITM than those in patients administered 0.2 mg of ITM.