Intrathecal morphine use in total knee arthroplasty in patients over 50 years old. A single-center experimental study.

Abstract

Introduction: Total knee arthroplasty causes intense postoperative pain. This study aims to evaluate the efficacy of intrathecal anesthesia with low-dose morphine hydrochloride in patients undergoing total knee arthroplasty.

Methods: The present experimental study was conducted at the Hospital Alcívar in Guayaquil, Ecuador, from January to December 2022 with patients older than 18 years who underwent total knee arthroplasty surgery and were randomized to receive an intrathecal injection of morphine at a dose of 0.1 µg/kg of weight (group 1) or morphine at a dose of 0.2 µg/kg (group 2). Analgesia was assessed using the analog pain rating scale (VAS). Side effects were measured. The proportions were compared with the chi-square test, and the medians were compared with the Mann‒Whitney U test.

Results: There were 22 women (55%) and 18 men (45%). The average age was 68.9 years. Low-dose intrathecal morphine had a significantly longer analgesia time (20 hours vs. 24 hours) and a substantially shorter anesthesia time (210 minutes vs. 300 minutes). Patients receiving low-dose intrathecal morphine also had equal VAS scores for intraoperative pain (1 vs. 1), immediate postoperative pain (1 vs. 1), and 24-hour postoperative pain (2 vs. 1). The incidence of hypotension, nausea, vomiting, and pruritus was similar in both groups.

Conclusions: Low-dose intrathecal morphine is a safe and effective option for postoperative pain control in patients undergoing total knee arthroplasty.