Onset, intensity of blockade and somatosensory evoked potential changes of the lumbosacral dermatomes after epidural anesthesia with alkalinized lidocaine

The onset and intensity of blockade of the lumbosacral dermatomes after epidural anesthesia with alkalinized lidocaine were investigated in a randomized, double-blind study in 26 patients. Control subjects (n = 13) received 20 mL of 1.37% lidocaine (1.5% lidocaine plus 1 mL saline per 10 mL lidocaine) with added 1:200,000 epinephrine; the solution pH was 6.20 ± 0.08. Patients in the alkalinized lidocaine group (n = 13) were given 20 mL of 1.37% lidocaine plus added bicarbonate (1 mL sodium bicarbonate per 10 mL 1.5% lidocaine) and 1:200,000 epinephrine; the solution pH was 7.18 ± 0.10. Posterior tibial nerve (PTN) somatosensory evoked potentials (SSEPs) and L5 and S1 dermatomal SSEPs of both lower extremities were done before and after the epidural. Alkalinization of lidocaine resulted in a significantly shorter time to block the L2, L4, L5, and S1 dermatomes. Motor blockade was significantly more profound in the alkalinized lidocaine group. Thirteen of 78 PTN and L5 and S1 dermatomal SSEPs were abolished in the alkalinized lidocaine group compared to 4 of 78 SSEPs in the nonalkalinized group. Alkalinization of lidocaine is recommended to shorten the time to block the L5-S1 dermatomes when epidural anesthesia is planned for lower extremity surgery.