Potential neurotoxicity of spinal anesthesia with lidocaine

Spinal (intrathecal) anesthesia has evolved into a safe, widely accepted method of anesthesia with many advantages. However, the past decade has seen a large number of case reports and incidence studies that implicate the local anesthetic (LA) lidocaine as being more neurotoxic than other commonly used LAs such as bupivacaine and tetracaine, based on patterns of clinical use current at the time of those reports. Available studies suggest a risk of persistent lumbosacral neuropathy after spinal lidocaine by single injection in about 1 in 1300 procedures and a risk as high as about 1 in 200 after continuous spinal anesthesia with lidocaine. While uncommon, this risk is probably an order of magnitude higher than the risk reported for other commonly used LAs or for general anesthesia. Spinal lidocaine is also implicated in the syndrome of transient neurologic symptoms (previously referred to as transient radicular irritation), manifest by pain or dysesthesia in the buttocks or legs after recovery from anesthesia. Although the pain typically resolves within 1 week without lasting sequelae, it can be severe in up to one third of patients with the syndrome. In addition to clinical studies, both whole animal and in vitro studies have shown that lidocaine can be neurotoxic at clinically available concentrations and that lidocaine is more neurotoxic than equipotent concentrations of other commonly used LAs. The mechanism of this neurotoxicity may involve changes in cytoplasmic calcium homeostasis and mitochondrial membrane potential.