The use of intrathecal morphine for acute perioperative pain in lower limb arthroplasty surgery: a survey of practice at an academic hospital

Abstract

Background and purpose of study Intrathecal morphine (ITM) provides optimal postoperative analgesia in patients who are scheduled for total knee and hip operation with spinal anaesthesia. However, the ideal dose at which maximal analgesic effect occurs with minimal side effects is not known. This study aimed to describe the use of two doses of ITM, and side effect profile in patients undergoing elective hip and knee arthroplasty. Methods This was a prospective, descriptive, and contextual study conducted on patients who had total hip and knee replacement at Chris Hani Baragwanath Academic Hospital from 1 September to 30 November 2020. The sample size consisted of 66 patients who were 18 years and older, American Society of Anaesthesiology (ASA) classification 1-3, patients who had received either 100 mcg or 150 mcg ITM dose under spinal anaesthesia and sent to the ward postoperatively. Visual Analogue Scale (VAS) score was used to assess pain in the first 24 hours, consumption of rescue analgesia and reported side effects were documented. Results There was no relationship between age, weight, ASA classification or type of surgery between VAS score classification groups. Patients who received 100 mcg ITM had a higher median VAS pain score 2 (1-5) compared to those who received 150 mcg ITM 1 (0-2), p = 0.01. The need for rescue analgesia between the two groups was marginally less in the 150mcg ITM group (p =0.098). There was no difference in the rate of side effects between the 100 mcg ITM group [12 (41%)] and the 150 mcg ITM group [17 (59%)], p = 0.92. Rescue analgesia was marginally iv different between groups, p = 0.09. There were no real differences in the VAS pain scores between the total knee and total hip surgeries. None of the patients experienced clinically significant respiratory depression. Conclusion The 150mcg ITM dose provided good analgesic effects with longer duration of action and comparable side effect profile to the 100mcg ITM dose. This dose was not associated with development of respiratory depression and can therefore administered safely to patients who are discharged to the ward postoperatively in a resource constraint environment.