Effect of dexmedetomidine as an adjuvant to bupivacaine in femoral nerve block for perioperative analgesia in patients undergoing total knee replacement arthroplasty: A dose–response study

CONTEXT: Dexmedetomidine is being increasingly used in nerve blocks. However, there are only a few dose determination studies. AIMS: To compare two doses of dexmedetomidine, in femoral nerve block, for postoperative analgesia after total knee arthroplasty (TKA). SETTINGS AND DESIGN: A prospective, randomized, controlled trial was conducted in the Department of Anesthesia at AIIMS, a Tertiary Care Hospital. MATERIALS AND METHODS: Sixty American Society of Anesthesiologists I–II patients undergoing TKA under subarachnoid block were randomized to three Groups A, B, and C. Control Group A received 20 ml (0.25%) of bupivacaine in femoral nerve block. Groups B and C received 1 and 2 μg/kg dexmedetomidine along with bupivacaine for the block, respectively. Outcomes measured were analgesic efficacy measured in terms of visual analog scale (VAS) score at rest and passive motion, duration of postoperative analgesia, and postoperative morphine consumption. Adverse effects of dexmedetomidine were also studied. STATISTICAL ANALYSIS USED: All qualitative data were analyzed using Chi-square test and VAS scores using Kruskal–Wallis test. Comparison of patient-controlled analgesia (PCA) morphine consumption and time to first use of PCA were done using ANOVA followed by Least Significant Difference test. A P < 0.05 was considered statistically significant. RESULTS: The VAS score at rest was significantly lower in Group C compared to Groups A and B (P < 0.05). There was no difference in VAS score at motion between Groups B and C. The mean duration of analgesia was significantly longer in Group C (6.66 h) compared to Groups A (4.55 h) and B (5.70 h). Postoperative mean morphine consumption was significantly lower in Group C (22.85 mg) compared to Group A (32.15 mg) but was comparable to Group B (27.05 mg). There was no significant difference in adverse effects between the groups. CONCLUSION: The use of dexmedetomidine at 2 μg/kg dose in femoral nerve block is superior to 1 μg/kg for providing analgesia after TKA, although its role in facilitating early ambulation needs further evaluation.