Potentiation of nerve block in vivo by physiological adjuvants in the solution.

One hundred and seventy-four rats received a standardized 0.4-ml injection into the left infraorbital nerve and all solutions contained lignocaine 0.25 g dl-1. In groups 1-4, the solutions were isoosmotic and contained, besides sodium chloride, potassium chloride 0 or 4 mmol litre-1 and glucose 0 or 20 mmol litre-1 (0 or 360 g dl-1). For groups 5-8, the solutions were hypoosmotic, containing sodium chloride to 0.6 of normal tonicity but were otherwise identical to solutions 1-4. Presence and duration of sensory block were determined from the reflex sublingual electromyographic response to periodic homolateral and contralateral electrical stimulation of the upper lip. In groups 1-4, the presence of potassium chloride 4 mmol litre-1 approximately doubled the duration of blockade (P less than 0.001). Groups 5-8 showed that hypoosmolarity also doubled the duration of block (P less than 0.001), but hypoosmolarity and potassium chloride did not have additive effects. It is concluded that addition of potassium- chloride 4 mmol litre-1 to isotonic solutions of lignocaine is likely to enhance their clinical effectiveness.