SLR - December 2016 - Jessica L. Olson

A Double-Blind Randomized Controlled Trial Comparing Dexamethasone and Clonidine as Adjuvants to a Ropivacaine Sciatic Popliteal Block for Foot Surgery

Reference: Vermeylen K, De Puydt J, Engelen S, Roofthooft E, Soetens, F, Neyrinck A, Van de Velde M. A Double-blind Randomized Controlled Trial Comparing Dexamethasone and Clonidine as Adjuvants to a Ropivacaine Sciatic Popliteal Block for Foot Surgery. Local Reg Anesth. 2016 May 5; 9:17–24.

Scientific Literature Review

Reviewed By: Jessica L. Olson, DPM
Residency Program: Grant Medical Center, Foot & Ankle Surgery, Columbus, OH 

Podiatric Relevance: Postoperative pain is ubiquitous to foot and ankle surgery procedures. Common modalities of postoperative pain management include local anesthetics, peripheral nerve blocks, opioid use and other medications (e.g., NSAIDs, acetaminophen, etc.). Popliteal peripheral nerve blocks are proven to be a reliable and safe intervention for postoperative pain control in foot and ankle surgery. However, their duration can be variable (range eight to 24 hours). The present study aims to assess the effect of the adjuvants, clonidine and dexamethasone (DXM), to ropivacaine on the duration of the popliteal sensory and motor nerve block.

Methods: The study used a double-blind randomized placebo-control design. The parameters evaluated were the analgesic effects of clonidine or DXM when added to ropivacaine for hallux valgus surgery. A total of 72 patients were randomized, and the data of 57 patients were statistically analyzed. All patients received an ultrasound-guided single-shot popliteal fossa block with a total of 31 mL, 30 mL of ropivacaine 0.75 percent, supplemented with either 1 mL of saline (control group), 1 mL of DXM (5 mg), or 1 mL of clonidine (100 μg). The block was performed 60 minutes prior to procedure and effects (sensory and motor) of the blocks were evaluated every five minutes until start of surgery and every 10 minutes after surgery until discharge. The primary end point was time to first pain sensation. Patient-reported pain scores were recorded using the visual analog scale (VAS), which ranged from 0 (no pain) to 10 (worst pain imaginable), with >3 indicating pain. Secondary end points were time to 1) complete sensory regression (i.e., return of normal sensation to toes) and 2) motor block regression (i.e., normal motor function of lower leg).

Results: Differences in age, tourniquet time and motor and sensory block onset times were evaluated by Kruskal-Wallis analysis. P-values >0.05 were considered statistically significant. The control group (n=17), the DXM group (n=19) and the clonidine group (n=21) did not differ in age, tourniquet time and block onset times. Demographics were consistent across groups. The duration to the first pain sensation was statistically significant (p=0.024) for both DXM (prolonged by nine hours) and clonidine (prolonged by six hours) compared to the saline control group. The time to complete sensory regression was statistically significant for DXM (p<0.001; prolonged by 12 hours) and for clonidine (p=0.005; prolonged by seven hours) compared to saline control group. Finally, the time to complete motor block regression was statistically significant for DXM (p<0.001; prolonged by 13 hours) compared to the saline control group.

Conclusions: Addition of DXM or clonidine to ropivacaine in popliteal peripheral nerve blocks significantly prolonged the duration of postoperative sensory and of motor block. The adjuvant of DXM prolonged the duration to the first pain sensation and the time to complete sensory regression and complete motor block regression. These effects were also observed for clonidine, but to a lesser extent. The short-term use of DXM has proven to be safe and successful in prolonging the duration of postoperative analgesia, as demonstrated by studies illustrating their vasoconstrictive properties, ability to block nociceptive impulses and anti-inflammatory effects. The effects of clonidine remain unclear; however, it is frequently used as an additive to local anesthetic. Given the present study findings, use of these adjuvants can increase the duration of a popliteal block, which may prove beneficial in larger foot and ankle reconstruction procedures, in patients with pain management concerns and in reducing costs associated with postoperative pain control. 

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