Abstract
Background and Aims: Managing the pain after a Total Knee Arthroplasty (TKA) is essential for early mobilization and rehabilitation, which plays a crucial role for better clinical outcomes. Epidural infusion of local anesthetic and opioids provides good pain relief but can lead to side effects such as hypotension, motor weakness and respiratory depression. The objective of this study was to evaluate if epidurally administered ketamine could provide postoperative analgesia, thereby, reducing the dose of epidural infusion and the need for rescue analgesia.
Methods: Thirty patients undergoing TKA under epidural anesthesia were randomized to receive 0.5% bupivacaine (Group I) or 0.5% bupivacaine + ketamine (0.5mg/kg) (Group II) as their primary anesthetic. At the end of the surgery, an infusion of 0.1% bupivacaine + fentanyl (1μg/ml) was started through the epidural catheter at 5ml/h. The rate was adjusted every 2 hours, depending on the pain experienced by the patient. If, despite rate adjustment, the patient graded the pain as 5 or more, morphine 5mg intramuscularly could be administered as the rescue analgesic.
Results: The dose of epidural infusion in the postoperative period between the 2 groups was comparable. Rescue analgesia was needed in 5 (35%) Group I and 8 (53%) Group II patients. An analysis of the subset of patients using the Kaplan-Meier curves, showed that most of the patients from Group I needed the rescue dose at the sixth hour. Few of the Group II patients also needed rescue analgesia at the sixth hour but their rate of needing rescue analgesic was gradual, lasting up to 18 hours.
Conclusion: This study showed that the addition of a single dose of ketamine (0.5mg/kg) did not improve postoperative analgesia after TKA. However, it may have some benefit in a select subset of patients.