Spinal Anesthesia with Bupivacaine and Tetracaine in Sheep

Spinal anesthesia was performed in sheep in order to compare hyperbaric solutions of 0.375 and 0.75% bupivacaine and tetracaine. There was no significant difference between the two compounds in the duration of sensory analgesia in the anal regions nor, at 0.75%, in the time required for complete regression of the block. However, at 0.375% the duration of sensory analgesia and motor block in the hind limbs and the time required for complete regression were shorter with bupivacaine. In addition to exhibiting a higher incidence and a longer duration of motor block in the hind limbs, the sheep that received tetracaine were unable to stand on the hind limbs even after complete regression of block had occurred. Although further studies are required to establish the cause of this phenomenon, we suggest this may reflect a block of proprioceptor fibers.