title: Additives to local anesthetics for peripheral nerve blocks: Evidence, limitations, and recommendations.
abstract: OBJECTIVE
  The therapeutic rationale, clinical effectiveness, and potential adverse effects of medications used in combination with local anesthetics for peripheral nerve block therapy are reviewed.
  
  
  CONCLUSIONS
  A wide range of agents have been tested as adjuncts to peripheral nerve blocks, which are commonly performed for regional anesthesia during or after hand or arm surgery, neck or spine surgery, and other procedures. Studies to determine the comparative merits of nerve block adjuncts are complicated by the wide variety of coadministered local anesthetics and sites of administration and by the heterogeneity of primary endpoints. Sodium bicarbonate has been shown to speed the onset of mepivacaine nerve blocks but delay the onset of others. Epinephrine has been shown to prolong sensory nerve blockade and delay systemic uptake of local anesthetics, thus reducing the risk of anesthetic toxicity. Tramadol, buprenorphine, dexamethasone, and clonidine appear to be effective additives in some situations. Midazolam, magnesium, dexmedetomidine, and ketamine cannot be routinely recommended as nerve block additives due to a dearth of supportive data, modest efficacy, and (in the case of ketamine) significant adverse effects. Recent studies suggest that administering additives intravenously or intramuscularly can provide many of the benefits of perineural administration while reducing the potential for neurotoxicity, contamination, and other hazards.
  
  
  CONCLUSIONS
  Some additives to local anesthetics can hasten the onset of nerve block, prolong block duration, or reduce toxicity. On the other hand, poorly selected or unnecessary additives may not have the desired effect and may even expose patients to unnecessary risks.
authors.affiliation: Neil S. Bailard, M.D., is Assistant Professor; Jaime Ortiz, M.D., is Assistant Professor; and Roland A. Flores, M.D., is Assistant Professor, Department of Anesthesiology, Baylor College of Medicine, Houston, TX.
authors.forename: Neil S
authors.initials: NS
authors.lastname: Bailard
authors.forename: Jaime
authors.initials: J
authors.lastname: Ortiz
authors.forename: Roland A
authors.initials: RA
authors.lastname: Flores
mesh_terms: D000759:Adjuvants, Anesthesia; D000316:Adrenergic alpha-Agonists; D000701:Analgesics, Opioid; D000779:Anesthetics, Local; D000893:Anti-Inflammatory Agents; D002047:Buprenorphine; D003000:Clonidine; D003907:Dexamethasone; D020927:Dexmedetomidine; D004338:Drug Combinations; D004837:Epinephrine; D019317:Evidence-Based Medicine; D006801:Humans; D007649:Ketamine; D017616:Magnesium Compounds; D008874:Midazolam; D009407:Nerve Block / Q000379:methods*; D010525:Peripheral Nerves / Q000187:drug effects*; D017693:Sodium Bicarbonate; D014147:Tramadol; D014662:Vasoconstrictor Agents
chemical_list: D000759:Adjuvants, Anesthesia; D000316:Adrenergic alpha-Agonists; D000701:Analgesics, Opioid; D000779:Anesthetics, Local; D000893:Anti-Inflammatory Agents; D004338:Drug Combinations; D017616:Magnesium Compounds; D014662:Vasoconstrictor Agents; D014147:Tramadol; D002047:Buprenorphine; D020927:Dexmedetomidine; D007649:Ketamine; D003907:Dexamethasone; D017693:Sodium Bicarbonate; D003000:Clonidine; D008874:Midazolam; D004837:Epinephrine