Note 11 — Chapter XX · ANESTHESIA AND ANESTHETICS, GENERAL AND LOCAL.

Magnesium Salts as Local Anesthetics.—Six years ago Meltzer discovered that magnesium salts have the property of inhibiting functional activity in nerve tissue, and in December, 1899, he announced that the intracerebral injection of magnesium sulphate in a rabbit caused paralysis without previous convulsions. He has recently announced the local anesthetic effect of small doses of a 25 per cent. solution of magnesium sulphate, an effect which lasts from one to two hours. It is the magnesium “ion” which possesses the anesthetic property, since the chloride and the bromides give the same effects.

These salts have this advantage over other local anesthetics that there is no primary period of excitation. Moreover, applied locally to nerve trunks they have the effect of “blocking” them; and when applied to the sciatic, pneumogastric, and other nerves, temporarily abolish their power of conducting influences, either motor or sensory. This effect is apparently due to the fact that the magnesium normally present in the tissues constantly exercises an inhibitory power over them, and that when thus applied from without they merely exaggerate the condition already present; thus, if this be true, affording an ideal anesthetic.

In December, 1905, Meltzer read a paper before the New York Academy of Medicine, announcing success with intraspinal injection of magnesium sulphate in 25 per cent. strength. Blake, of New York, promptly made use of the suggestion in a child with tetanus. Two injections of antitoxin had been made into the cervical cord on successive days, with apparently no effect. He then made lumbar puncture and a subdural injection of magnesium sulphate, giving 1 Cc. of 25 per cent. solution for every twenty-five pounds of body weight, administering it every thirty-six hours, employing four doses. The effect was marked, in immediate control of convulsions, which, however, was not permanent; hence the repetition of the doses. How much influence the previous antitoxin had produced does not appear.

Meltzer suggests that the best time for an operation is three or four hours after a spinal injection. He reports four cases thus operated, in one of which, after the operation, the patient passed into a period of deep general anesthesia, in which he remained for five hours, the pulse keeping up, the respirations falling to ten per minute. In this case another spinal puncture was made, some of the spinal fluid let out, and the spinal cavity treated by repeated irrigations with sterile salt solution.

Meltzer’s few but important experiences indicate that at least three or four hours should be allowed to elapse after the introduction of the magnesium solution. He advises 1 Cc. for every twenty-five pounds of body weight, for intraspinal injection, which causes not only analgesia but temporary paralysis of the legs, sensation and motion returning in from eight to fourteen hours, with possible retention of urine for a day or two, requiring the use of the catheter.

Doses a little larger than the above, he thinks, would permit the performance of extensive operations in the abdominal cavity, or even higher up, without the aid of a general anesthesia. He is inclined to think that it would be preferable not to wait four hours, but to operate within about two hours after injection, with the aid of a small amount of chloroform, the operation to be followed by another puncture, with the removal of at least as much fluid as was introduced, and irrigation with sterile salt solution, finally leaving some of it within the canal.