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

Abstract 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