Intravenous and Perineural Dexamethasone in Peripheral Nerve Block

To the Editor In a recent trial comparing the effect of perineural and IV dexamethasone to placebo with sciatic nerve block, Rahangdale et al.1 reported no observable difference in the quality of postsurgical recovery measured by the quality of care score associated with dexamethasone via either route. Given the comparability with systemic administration, the lack of clinical benefit, and the potential for neurotoxicity, the authors concluded that the use of perineural dexamethasone be further evaluated. The issue of neurotoxicity attributed to dexamethasone deserves further scrutiny. The quoted article by Williams et al.2 examined in vitro neuronal death when exposed to ropivacaine and several other perineural adjuvants either alone or in combination. Williams et al.2 demonstrated that when doubling the concentration of dexamethasone from 66 to 133 mcg/mL, increased neuronal death was observed. The authors raised this concern but failed to mention that clonidine and buprenorphine were also present in the same mixture and that the increased neuronal death was not observed with dexamethasone and ropivacaine alone. A synergistic effect could not be ruled out, and the blame should not be attributed solely to dexamethasone. Attention was also drawn to the fact that 133 mcg/mL would be considered a subclinical dose, given that 8 mg of dexamethasone translates to a concentration of 220 to 363 mcg/mL. Williams et al.2 observed no significant cell death with 667 mcg/mL of dexamethasone alone at 24 hours nor was there additional cell death when combined with ropivacaine at 2 hours with that concentration. It therefore seems plausible that dexamethasone contributes to ropivacaine-induced cell death only in the presence of other adjuvants. The ideal adjuvant to peripheral nerve blockade should increase block duration and/or decrease local anesthetic dose. Perineural dexamethasone remains an off-label use and should be used cautiously only in select patients who may benefit from extended duration analgesia and in whom continuous catheter techniques are inappropriate or contraindicated. IV administration is preferable if it is truly equivalent to perineural administration for analgesic outcomes and if there is neurotoxicity. However, it may be premature to conclude the 2 routes equivalent based on recent studies which are underpowered for equivalence.1,3 Additional studies need to be conducted to definitively answer the questions of administrative route, neurotoxic dose, and clinical benefit. Steven Lee, MD, FRCPC Stephen Choi, MSc, MD, FRCPC Department of Anesthesia Sunnybrook Health Sciences Centre University of Toronto Toronto, Ontario, Canada [email protected]

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