Observations on sensory and sympathetic function during intrathecal analgesia

Abstract

A dilute solution of procaine in glucose solution was injected by slow drip into the lumbar theca of patients to cause a differential block. Vasodilatation of the skin vessels of the lower limbs always occurred before any change in sensibility. The first changes in sensibility were inability to feel painful stimuli and warm stimuli; these two forms of sensibility were usually coextensive and occurred at the same time. When this was not so, either form of sensibility could be more extensively disturbed than the other. When warmth sensibility was removed, cold sensibility was either normal or diminished or cold stimuli caused nonthermal sensations such as nonthermal wetness or pressure. It is concluded that the nerve fibers signalling warmth are the smaller delta fibers or nonmyelinated fibers or both. As two groups of investigators who recorded from the nonmyelinated fibers in man found no nonmyelinated fibers responding to cold, it is concluded that fibers signalling cold cover the same delta range as those signalling warmth, together with a proportion of larger delta fibers. When fibers subserving pain, warmth, and cold were blocked, tactile sensibility could be normal. It is concluded that, if there are tactile fibers in man in the smaller delta and nonmyelinated ranges, their contribution to tactile sensibility is insignificant. It is also concluded that the preganglionic B fibers are the most susceptible of all fibers of the nerve roots to local anesthetic agents. On two occasions, piloerection occurred when the preganglionic sympathetic fibers were blocked. In two patients spontaneous itching occurred when all peripheral nerve fibers were blocked except large tactile fibers.