Perineural dexamethasone successfully prolongs adductor canal block when assessed by objective pinprick sensory testing: A prospective, randomized, dose-dependent, placebo-controlled equivalency trial.

STUDY OBJECTIVE: To determine whether perineural dexamethasone prolongs peripheral nerve blockade (PNB) when measured objectively; and to determine if a 1 mg and 4 mg dose provide equivalent PNB prolongation compared to PNB without dexamethasone.

SETTING: Multiple studies have reported that perineural dexamethasone added to local anesthetics (LA) can prolong PNB. However, these studies have relied on subjective end-points to quantify PNB duration. The optimal dose remains unknown. We hypothesized that 1 mg of perineural dexamethasone would be equivalent in prolonging an adductor canal block (ACB) when compared to 4 mg of dexamethasone, and that both doses would be superior to an ACB performed without dexamethasone.

DESIGN: This was a prospective, randomized, double-blind, placebo-controlled equivalency trial involving 85 patients undergoing a unicompartmental knee arthroplasty.

INTERVENTIONS: All patients received an ACB with 20 ml of 0.25% bupivacaine with 1:400,000 epinephrine. Twelve patients had 0 mg of dexamethasone (placebo) added to the LA mixture; 36 patients had 1 mg of dexamethasone in the LA; and 37 patients had 4 mg of dexamethasone in the LA.

MEASUREMENTS: The primary outcome was block duration determined by serial neurologic pinprick examinations. Secondary outcomes included time to first analgesic, serial pain scores, and cumulative opioid consumption.

MAIN RESULTS: The 1 mg (31.8 ± 10.5 h) and 4 mg (37.9 ± 10 h) groups were not equivalent, TOST [Mean difference (95% CI); 6.1 (-10.5, -2.3)]. Also, the 4 mg group was superior to the 1 mg group (p-value = 0.035), and the placebo group (29.7 ± 6.8 h, p-value = 0.011). There were no differences in opioid consumption or time to analgesic request; however, some pain scores were significantly lower in the dexamethasone groups when compared to placebo.

CONCLUSION: Dexamethasone 4 mg, but not 1 mg, prolonged the duration of an ACB when measured by serial neurologic pinprick exams.

CLINICAL TRIAL REGISTRATION: NCT02462148.