Differential Spinal Block. Ii. The Reaction of Sudomotor and Vasomotor Fibers 1

Abstract

In a previous communication (1), a technic was described for differentially blocking axones as they traverse the subarachnoid space. This was based upon the assumption that the smaller, unmyelinated fibers would be more susceptible to an anesthetic agent in the spinal fluid than the larger, myelinated fibers. At that time, we tested motor power and the patient's appreciation of pin-prick, touch, deep pressure, position sense, and vibratory sense. Skin temperature measurements were used as the index of vasomotor fiber block. It was found that when a 0.2 per cent solution of procaine hydrochloride was used, vasomotor fibers and pin-prick fibers were blocked while motor power and the modalities of touch, deep pressure, position sense, and vibratory sense remained unaffected.Emmett (2) presented a series of cases in which it was rarely possible to produce a sensory and sympathetic block without a motor block by giving a small volume of procaine solution in the usual high concentrations. Unfortunately, however, the various sensory modalities were not individually examined and the observations on the results of the block were confined to the feet.Gasser and Erlanger (3), working with cocaine, and Heinbecker, Bishop, and O'Leary (4), working with procaine, have demonstrated that the class C fibers, the least myelinated of a mixed nerve, are the first to be blocked when subjected to local infiltration with the anesthetic agent. It does not necessarily follow that these fibers (in which class autonomic fibers generally fall) are blocked by a lower concentration, but it does suggest that this is so and that, therefore, these fibers could be preferentially blocked.In this laboratory, preliminary experiments performed on the cat indicated that this was true. A powerful sympathogenic reflex, the carotid sinus 1 Presented at the Ether Day Centenary at the Massachusetts General Hospital on October 15, 1946. reflex, could be abolished in the vagotomized cat by a 0.15 per cent procaine perfusion of the spinal canal [after the method of CoTui (5)], at a time when the animal maintained spontaneous respiratory activity and gave a contralateral muscular response to the electrical excitation of one femoral nerve.The experiments of Judovich and Bates (6) are interesting in this connection. They demonstrated that varying the concentrations of ammonium chloride surrounding the saphenous nerve of the cat exerted a partially selective effect in obliterating the action potentials of the A and C type fibers. They did not clearly demonstrate that this was not a time gradient as in the work mentioned above. The selective effect of the pitcher plant distillate and ammonium salts, peripherally and intraspinally, in relieving neuralgic pain while leaving the usually tested sensations unimpaired is most stimulating; but the mechanism and fiber types involved are not clear.This report is concerned mainly with the selective effect, on the basis of a graded concentration, on sudomotor, vasomotor and pin-prick fibers in the subarachnoid space. MAT...

Studies on Autonomic Blockade. Ii. Observations on the Nature of Blood Pressure Fall With High Selective Spinal Anesthesia in Pregnant Women 1

“…Most investigators (3,16,29) believe that such bradycardia is caused by a blockade of the cardioaccelerator fibers which can be accomplished even with a low concentration of procaine (8,9).…”

The Effect of High Spinal Anesthesia on the Renal Hemodynamics and the Excretion of Electrolytes During Osmotic Diuresis in the Hydropenic Normal Pregnant Woman 1

“…Instead there was a tendency toward vasoconstriction as is indicated by a rise in the renal arterial resistance. Since the spinal blockade is effective in blocking autonomic vasoconstrictor fibres (1,29,30) it must be inferred that this increase in renal vasoconstriction is caused by a compensatory mechanism which is probably humoral in nature. This hypothesis has been suggested previously (1), following the observation that the blood pressure frequently returns to normal levels despite the maintenance of a high spinal anesthesia.…”

Studies on Autonomic Blockade. I. Comparison Between the Effects of Tetraethylammonium Chloride (Teac) and High Selective Spinal Anesthesia on Blood Pressure of Normal and Toxemic Pregnancy 1

“…It also allowed the elevation of sensory anesthesia to high levels with a consequent satisfactory autonomic blockade. Sarnoff and Arrowood (15)(16)(17)(18) have repeatedly demonstrated that such low concentration of procaine blocks selectively the unmyelinated fibers, i.e., the vasoconstrictor fibers and those which mediate pinprick sensation. They also suggested that the fibers concerned with the temperature sensation might also be blocked.…”