Evaluation of Analgesic Effects of Ketamine versus Dexmedetomidine as an Adjuvant to 0.2% Ropivacaine Infusion in Adductor Canal Block for Postoperative Analgesia following Unilateral Total Knee Replacement Surgery

BACKGROUND: Postoperative pain management is critical for recovery following total knee replacement (TKR). Significant pain following surgery is linked to TKR, and this discomfort might have a negative impact on the patient's satisfaction, length of stay, and functional recovery. The adductor canal block (ACB) is preferred for its motor-sparing properties. This study compared the analgesic efficacy of ketamine and dexmedetomidine as adjuvants to ropivacaine infusion in ACB for patients undergoing unilateral TKR. METHODS: In this prospective, randomized, comparative study, 44 patients (American Society of Anesthesiologists I-III) were divided into two equal groups. All received spinal anesthesia followed by an ultrasound-guided ACB with a catheter. Group A received 0.2% ropivacaine with ketamine (1 mg/kg) infusion, and Group B received 0.2% ropivacaine with dexmedetomidine (1 μg/kg) infusion at 8-10 mL/h for 24 h. Primary outcomes included a comparison of the requirement for rescue analgesia, while secondary outcomes included a comparison of pain scores, hemodynamic stability, and motor blockade. RESULTS: The requirement for rescue analgesia was significantly higher in Group A (54.54%) compared to Group B (18.2%; P = 0.012). While numerical pain scores were generally comparable, Group B showed significantly lower pain at the 8th h (P = 0.045). Both groups maintained hemodynamic stability and demonstrated preserved motor power. Postoperative vomiting was significantly more frequent in Group A (P = 0.035). CONCLUSION: Dexmedetomidine (1 μg/kg) is a more effective adjuvant than ketamine (1 mg/kg) for ropivacaine-based ACB, offering improved analgesia without adverse hemodynamic or motor effects.