Spinal 2-chloroprocaine: Minimum effective dose

Recent studies using preservative-free 2-chloroprocaine (2-CP) for spinal anesthesia have shown it to be a reliable short-acting agent in the 30-mg to 60-mg range. Investigations of doses below this range have not been performed. To establish the minimum effective dose for spinal anesthesia, this randomized, double-blind, crossover study investigates the characteristics of spinal 2-CP 10 mg and 20 mg in 8 volunteers and compares the results with previous data obtained for 30 to 60 mg in the same human model. Peak block height, regression to L1, tolerance to tourniquet, and transcutaneous electrical stimulation all increased with increasing doses from 10 to 60 mg (P <. 0001). Likewise, time to complete block regression, ambulation, and micturition also increased with increasing spinal 2-CP dosage (P <. 0001). Degree of motor block generally increased with increasing doses from 10 to 60 mg; however, no differences existed between the 20-mg and 30-mg and between the 40-mg and 60-mg doses. Spinal 2-CP 40 mg and 60 mg provide rapid and reliable sensory and motor block. Although the 20-mg and 30-mg doses can produce sensory anesthesia adequate for brief surgical procedures, less motor block and some sacral sparing should be anticipated. Because the 10-mg dose produces only brief and inconsistent sensory anesthesia, it can be considered a no-effect dose.