Local analgesics do not cause any direct nerve fairly damage unless they are injected intraneurally or given in higher concentrations than that which is commercially available. Several different laboratory models have proven
that all local analgesics can be neurotoxic but that more lidocaine and tetracaine are potentially more neurotoxic than bupivacaine . The pathogenesis Inhibitors,research,lifescience,medical of local analgesics-induced local tissue toxicity is poorly understood. There appears to be a relationship between concentration and neurotoxicity. In 1985, Ready et al.  evaluated the neurotoxic effects of single injections of local analgesics in rabbits. They reported that spinal cord histopathology remained normal and that persistent neurologic deficits were not seen with clinically used concentrations of tetracaine, lidocaine, bupivacaine, or chloroprocaine. However, histopathologic changes and neurologic deficits did occur with higher concentrations of tetracaine (1%, up to 8%) and lidocaine (8%, Inhibitors,research,lifescience,medical up to 32%). It was found that high concentrations of lidocaine (and tetracaine) caused neural injury. Notably, in this model, extensive neurologic impairment was not necessarily accompanied by equally extensive
lesions in the spinal cord and nerve roots, thus demonstrating the need for multiple models Inhibitors,research,lifescience,medical to fully assess neurotoxicity. Particularly, the highest concentration of bupivacaine (3.3%) was not consistently associated with comparable neural damage. Peripheral nerve injury is a rare complication of regional anesthesia. The pathogenesis of local analgesics-induced local tissue toxicity is poorly understood. The mechanism of this enhanced toxicity remains to be established, but it may be related to an effect of
diverse vasoconstriction Inhibitors,research,lifescience,medical on anesthetic exposure . Ischemia is one of the possible causative mechanisms which may result from changes in peripheral blood flow caused by a vasopressor adjuvant such as epinephrine. Some believe Inhibitors,research,lifescience,medical that this neurological damage is a result of spinal cord ischemia either due to prolonged hypotension during surgery or as a consequence of arterial constriction resulting from Dacomitinib the use of epinephrine in the local anesthetics solution . The use of additives in the solution also has been implicated as contributing factors. The pressure of the injected agent may cause nonspecific pressure-related nerve damage. An immune-mediated mechanism may be possible as suggested by others [4, 16]. In Brummett’s study, rat sciatic nerves were harvested at either 24 hours or 14 days after injection and analyzed for perineural inflammation and nerve damage. When compared with the saline control group, the bupivacaine group had significantly higher perineural inflammation scores at 24 hours. Nerves in the bupivacaine and dexmedetomidine group showed less perineural inflammation at 24 hours when compared to the bupivacaine group.