Adjuvant dexamethasone for bupivacaine sciatic and ankle blocks: results from 2 randomized placebo-controlled trials

Dexamethasone as a local anesthetic adjuvant has been shown to prolong the time to first postoperative pain and improve postoperative analgesia following upper-limb brachial plexus block. However, the lack of systemically administered dexamethasone in controls makes interpretation of previous studies difficult. We performed 2 prospective, randomized, double-blind, placebo-controlled trials to test whether the addition of dexamethasone 8 mg to bupivacaine for sciatic and ankle blocks prolongs block duration, improving postoperative analgesia.

One hundred twenty-six patients presenting for elective foot/ankle surgery under sciatic (n = 66) or ankle blocks (n = 60) received 30 mL bupivacaine 0.5% + dexamethasone 8 mg or saline 2 mL. Alternate solutions were administered by intramuscular injection into the ipsilateral thigh. Outcomes assessed at 24 and 48 hours included pain onset, numerically rated pain, and supplementary tramadol consumption.

For the sciatic study, fewer dexamethasone group patients experienced pain at 24 hours (13% vs 47%, P = 0.01), an effect supported by multiple post hoc analyses for pain from 20 to 34 hours. No benefit existed at 48 hours or at any time for the ankle block. For each study, pain-free survival curves for the first 48 hours were not significantly different between groups. Pooled analysis of the 2 individual studies further supported the absence of a significant dexamethasone effect: hazard ratio (0.81; 95% confidence interval, 0.58-1.53; P = 0.94). For both studies, there were no differences between groups for all other study outcomes including worst and average pain, the requirement for tramadol, and patient satisfaction.

Substitution of systemic dexamethasone for perineural dexamethasone during bupivacaine sciatic and ankle blocks had only a minor analgesic enhancing effect. Given recent animal studies showing dexamethasone neurotoxicity, the perineural route for dexamethasone administration requires reevaluation.