A chronic model for investigation of experimental spinal anesthesia in the dog

A chronic model for investigation of spinal anesthesia in the dog is described. This model incorporates the use of a chronically implanted catheter in the lumbar subarachnoid space. An 18-gauge thin-walled Crawford needle is passes percutaneously into the subarachnoid space. An 18-gauge epidural catheter is then threaded through the needle into the subarachnoid space and the distal end attached to a special metal valve which is sutured under the skin. One-milliliter volumes of various local anesthetic solutions were injected intrathecally via the valve and catheter. Durations of the effects of the local anesthetics were evaluated. Duration which hind-limb paralysis persisted in the dog. The times to onset and durations of motor blockades were evaluated following the intrathecal injection of dibucaine, tetracaine, lidocaine, bupivacaine, chloroprocaine, and mepivacaine. Times to onset ranged from 1.1 to 2.3 min. Durations of motor blockade were longest for dibucaine and tetracaine, followed in order of decreasing duration by bupivacaine, lidocaine, chloroprocaine, and mepivacaine. The durations of subarachnoid conduction motor blockades in the dog are qualitatively similar to reported values for spinal anesthesia in man. Therefore, the technique described may provide a useful model to evaluate factors that may influence spinal anesthesia.