Sympathetic recovery following lumbar epidural and spinal analgesia.

During recovery from spinal and epidural block, the progressive reduction of digital blood flow is regarded as evidence of sympathetic recovery of the extremity. This was demostrated by the decreasing amplitude of a digital pulse-wave (photoelectric plethysmographic) recording. As the level of analgesia regressed to T8-11 following spinal or epidural block, the toe pulse-wave amplitudes began to decrease. In the presence of good motor and sensory block in the lower extremity with low spinal or epidural anesthesia (level of analgesia T-11 or below), the clinical or photoeletric plethysmographic evidence of sympathetic denervation was minimal or absent. According to these findings, the authors postulate that some preganglionic sympathetic fibers which conduct sympathetic stimulation to the lower extremity originate at spinal cord segments T-10 or above.