Low dose ketamine infusion for postoperative analgesia after total knee arthroplasty: Optimum dose reducing morphine consumption?

Background and aim: In this study, it's aimed to find the optimal dose that reduces morphine consumption as a result of continuous i.v. ketamine infusion in different doses for postoperative analgesia, and to evaluate the side effects, discharge time, patient satisfaction and recovery. Methods: After the approval of the ethics committee, 75 female over 18 years of age with ASA I-III scheduled for TKA were included in the study. The study was conducted prospectively, randomly, and double blind. After spinal anesthesia, 2 μg, 4 μg, 6 μ / kg / min were started in 25 patients in Group I, Group II and Group III, respectively. The ketamine that was started was reduced to half at the end of the surgery and administered until the 48th postoperative hour. Postoperative analgesia was provided with PCA morphine. Vitals, complications, morphine consumption, VAS, discharge time, patient satisfaction with 90° active knee flexion were recorded during the application. Results: There was no difference between the groups in terms of demographic and hemodynamic data. In this study, the difference between the 48-hour cumulative morphine consumption of Group III (38.96 ± 6.08 mg), Group II (45.52 ± 8.23 mg) and Group I (53.92 ± 5.49 mg) was significant (p = 0.001). Group III; 27% compared to Group II and Group I; Group II used 15% less morphine than Group I. During the postoperative follow-up processes, the groups at rest VAS <40mm. While motion VAS at 12 hours and discharge time were found to be more effective and meaningful in Group II compared to Group I, rest VAS at postoperative 6, 12, 24, 48 hours and 6 weeks, motion rVAS at 6 and 12 hours, discharge time and active knee flexion were more effective than Group I at only Group III dose (p≤0.05). Conclusion: In this study, it was concluded that in the postoperative management of TKA, the optimal dose of ketamine that reduces morphine consumption that will provide optimal analgesia and rehabilitation without side effects is Group III. Keyword: Total knee arthroplasty, ketamine, morphine, postoperative analgesia