SLR - December 2017 - Amanda L. Killeen
Reference: Vermeylen K, De Puydt J, Engelen S, et al. A Double-Blind Randomized Controlled Trial Comparing Dexamethasone and Clonidine as Adjuvants to a Ropivacaine Sciatic Popliteal Block for Foot Surgery. Local and Regional Anesthesia. 2016;9:17–24.Scientific Literature Review
Reviewed By: Amanda L. Killeen, DPM
Residency Program: Southern Arizona VA Health Care System, Tucson, AZ
Podiatric Relevance: Popliteal blocks are commonly given in lower-extremity surgery. Adding adjuvants to local anesthetics can extend the length of both the sensory and motor block, decreasing postop pain and the need for opioids. Dexamethasone (DXM) nearly doubles the length of interscalene blocks and short-term IV DXM reduces pain without hyperglycemia. Clonidine has been used in popliteal blocks without side effects in doses less than 150 µg. This study aims to show the length of block elongation with each of these adjuvants compared to saline placebo.
Methods: A double-blind randomized controlled study comparing the use of clonidine 100 µg or DXM 5 mg as an adjuvant to 30 cc ropivacaine 0.75 percent in popliteal blocks for hallux valgus surgery performed by the same surgeon. Seventy-two female patients were assigned to groups—clonidine, DXM, saline—and 57 were statistically analyzed. An ultrasound-guided sciatic nerve block at the popliteal fossa was given 60 minutes prior to the surgery, and a research assistant evaluated sensory and motor block every five minutes before, and every 10 minutes after, the case. Patients were excluded if they broke protocol, exhibited NSAID intolerance, were allergic to local anesthetics or had diabetes, peripheral neuropathy, coagulation disorders or impaired kidney function. All patients were ASA classification 1 or 2.
Results: Compared to saline placebo, duration to first pain sensation was increased by nine hours with DXM and six hours with clonidine. Compared to saline, sensory and motor blockade with DXM was 12 and 13 hours, respectively, and seven and two hours, respectively with clonidine. Sensory block regression time was found to be statistically significant: six hours with DXM and two hours with clonidine. There was no difference in age, tourniquet time or block onset times.
Conclusions: The authors conclude that adding 5 mg DXM to 30 cc ropivacaine 0.75 percent lengthens popliteal blocks more than 100 µg clonidine. The combination of the two may exhibit synergistic effects but were not studied in this article. Extending the length of block is ultimately the goal for ameliorating postoperative pain and can decrease the need for opioids. Further study needs to be done on glucose metabolism when using DXM in populations with diabetes.