Bruno J. Urban

Clinical Observations Suggesting a Changing Site of Action during Induction and Recession of Spinal and Epidural Anesthesia

The cephalad borders of analgesia were determined 0.75 to 4 hours following the induction of spinal or lumbar epidural anesthesia. Levels thus obtained followed a straight line best described by the skin intercept of a transverse section through the trunk. They differed markedly from the dorsolaterally slanting pattern of segmental analgesia commonly associated with these blocks and observed during the onset of analgesia. There was no difference between spinal and epidural anesthesia in his regard. It is suggested that local anesthetics act first upon radicular structures and later upon structures inside the spinal cord. Because of different rates of anesthetic uptake and elimination, cord blockade becomes clinically apparent after the block of the more peripheral structures has worn off.