Determination Of The Efficacy And Side-effect Profile Of Lower Doses Of Intrathecal Morphine In Patients Undergoing Total Knee Arthroplasty

Abstract

Background: Intrathecal (IT) morphine provides excellent post-operative analgesia, but causes multiple side effects including nausea and vomiting (PONV), pruritus and respiratory depression, particularly at higher doses. The lowest effective dose of spinal morphine in patients undergoing total knee arthroplasty is not known.

Methods: We evaluated the analgesic efficacy and side effect profile of 100 - 300 μg IT morphine in patients undergoing elective total knee replacement in this prospective, randomized, controlled, double-blind study. Sixty patients over the age of 60 undergoing elective knee arthroplasty were enrolled. Patients were randomized to receive spinal anaesthesia with 15 mg Bupivacaine and IT morphine in three groups: (i) 100 μg; (ii) 200 μg; and (iii) 300 μg.

Results: Both 200 μg and 300 μg IT morphine provided comparable levels of postoperative analgesia. However, patients that received 100 μg had greater pain postoperatively, with higher pain scores and a greater requirement for supplemental morphine. There were no differences between groups with regard to PONV, pruritus, sedation, respiratory depression or urinary retention.

Conclusion: Both 200 μg and 300 μg provided comparable postoperative analgesia, which was superior to that provided by 100 mug IT morphine in patients undergoing total knee arthroplasty. Based on these findings, we recommend that 200 μg IT morphine be used in these patients.

Trial registration: ClinicalTrials.gov Identifier NCT00695045.

Figures

Figure 1

Mean (+/- SEM) postoperative visual analogue scale (VAS) pain score in each group, measured every 4 hours, for the first 24 postoperative hours. * Indicates significantly higher Area under VAS-Time curve compared to the 200 μg and 300 μg IT Morphine groups (P = 0.006, one way ANOVA).

Figure 2

Dot plot of postoperative requirement for supplemental morphine over the first 24 postoperative hours for each patient in each group. The middle line for each group represents the median value. * Indicates significantly higher morphine requirements compared to the 200 μg and 300 μg IT Morphine groups (P = 0.001, Kruskall-Wallis one way ANOVA on ranks).

Figure 3

Incidence of side-effects, including arterial desaturation below 90%, urinary retention, postoperative nausea and vomiting (PONV) and pruritus in each group over the first 24 postoperative hours (P > 0.05, Chi Square, for all comparisons).