Evaluation of Subarachnoid 2-Chloroprocaine and Sodium Bisulfite in the Rat

Abstract

Clinical reports have described prolonged and irreversible neurologic paralysis when the local anesthetic 2-chloroprocaine containing sodium bisulfite was injected unintentionally into the subarachnoid space instead of the epidural space. This study evaluated the effects of subarachnoid injections of chloroprocaine and sodium bisulfite, in combination and individually, in a rat model. Thirty-nine rats were chronically implanted with subarachnoid catheters that ended in the lumbar region and were allocated to one of the 7 following treatment groups: (1) physiologic saline; (2) 3% 2-chloroprocaine; (3) 3% 2-chloroprocaine plus 0.2% sodium bisulfite; (4) 3% 2-chloroprocaine plus 0.6% sodium bisulfite; (5) 0.2% sodium bisulfite; (6) 0.6% sodium bisulfite; or (7) 1.2% sodium bisulfite. The osmolarity of each solution was kept constant by varying the sodium chloride concentration, and the pH was adjusted to 3. All solutions at a fixed volume of 40 μL were injected into freely moving animals. Physiologic saline at pH 3 had no effect on any animal tested. Three percent 2-chloroprocaine alone or in combination with 0.2% sodium bisulfite caused reversible motor and sensory blockade of the hindlimbs and tail, with all animals recovering within 45 minutes. Three of five animals treated with 0.2% sodium bisulfite alone exhibited motor deficits only, and all recovered within 30 minutes. Ten of 15 animals tested with 2-chloroprocaine plus 0.6% sodium bisulfite or 0.6% sodium bisulfite alone exhibited motor deficits for greater than 45 minutes, with three lasting for more than 24 hours. Sodium bisulfite 1.2% caused irreversible hindlimb deficits in two of three animals. In conclusion, subarachnoid sodium bisulfite in concentrations of 0.6% or higher cause prolonged neurologic deficits in the rat. Three percent 2-chloroprocaine alone or with 0.2% sodium bisulfite causes only the expected reversible local anesthetic effect in this particular animal model.