Effect of pH on spinal anesthesia with lidocaine in sheep

Abstract Spinal anesthesia was performed in sheep with solutions of 1.5 and 5% lidocaine that had been adjusted to pH 4, 5 or 6.5. With the 1.5% solutions, durations of sensory analgesia were shortest at pH 4 and longest at pH 6.5; durations of motor block, on the other hand, were longer at pH's 4 and 5 than at 6.5. In general, the differences were small and indicative only of trends. With 5% solutions, durations of sensory and motor block were longer at pH 4 than at 6.5. Frequency of motor block in the hind limbs was higher at pH's 4 and 5 than 6.5. The mean duration of motor block was significantly longer at pH 4 than at 5 and also significantly longer at pH 5 than at 6.5.