Preganglionic Sympathetic Blockade in Man: A Study of Spinal Anesthesia

Torsten Gordh is without doubt today one of the most distinguished names in anesthesiology throughout the world. Few indeed are those who have done so much to establish anesthesiology as an integral part of the practice of modern clinical medicine both here and abroad. Few indeed are those who have done so much to establish anesthesiology as a true scientific discipline deserving of the best that modern science can offer in the way of original thought and imaginative research. I first encountered the name of Torsten Gordh when I began the study of anesthesia more than 30 years ago. I rapidly developed a high personal regard for his many contributions. Time has done nothing to diminish this respect. I have also been fortunate enough to have met and corresponded with him often enough so that today I regard him as a friend. It is thus a special privilege and honor to present a lecture which honors one so richly deserving of the kudos ofthe international community of anesthetists. It is only, however, with trepidation that I undertake to honor such a giant in our field, such a quintes$ential gentleman and scholar, and especially to do so by discussing certain aspects of spinal anesthesia, a field in which Dr Gordh has made so many original and important observations. Spinal anesthesia today occupies a special niche in anesthesiology. With the obsolescence of ether, spinal anesthesia represents a technique that we have had, collectively speaking, more experience with than any other modern anesthetic method. Spinal anesthesia has been employed world-wide for over 75 years. No other technique enjoys such an enviable track record. Indeed, I think it unlikely that many, if indeed any, of the anesthetic techniques and agents that currently enjoy such clinical popularity and pre-eminence will also still be used 75 years after they were first introduced. Our pttitudes towards spinal anesthesia have, however, not remained static over the last three-quarters of a century. Its popularity has waxed and waned. Our understanding of the indications and contraindications of spinal anesthesia are even now still changing. But we have, I believe, today developed considerable insight into the special attributes of spinal anesthesia. It is these that I would like to consider. Specifically, I would like to consider what we have recently learned that gives us new insight into physiologic changes associated with spinal anesthesia, and how this insight has altered our concepts of the clinical application of spinal anesthesia. The sensory denervation and profound somatic motor relaxation associated with spinal anesthesia constitute, of course, its raison #&re. But the safety and clinical utility of spinal anesthesia are determined by the physiologic changes which may accompany it. Unless the basis for these physiologic changes is fully understood, spinal anesthesia may lose its many advantages and may even become a potentially lethal choice of anesthesia. The physiologic responses to spinal anesthesia are due almost entirely to the fact that the local anesthetic injected into the subarachnoid space not only blocks somatic sensory and motor fibers, it also produces preganglionic sympathetic denervation. Preganglionic sympathetic denervation is the hallmark, physiologically speaking, of spinal anesthesia. Aspects of this sympathetic denervation deserve comment. First, it is now well established that the level of sympathetic denervation during hyperbaric spinal anesthesia is more extensive than is the level of sensory anesthesia. This is because of two facts. The first of these is the fact that the concentration of local anesthetic in spinal fluid decreases as a function of distance from the site of injection. The second fact is that different types of nerve fibers are blocked by different concentrations of local anesthetics.