Continuous anesthesia by subcutaneous injection of magnesium sulphate in nephrectomized animals

In the paper dealing with the anesthesia produced in animals by subcutaneous injection of magnesium salts Meltzer and Auer stated that animals which urinated frequently had the better chance for recovery, and that urination probably carries off some of the salt and prevents its fatal accumulation in the blood. On the basis of this assumption a series of experiments were carried out in which the anesthetic effects of subcutaneous injections of magnesium sulphate were studied in nephrectomized rabbits. The results briefly stated were as follows:

A dose of 0.8 gram of the salt per kilo of rabbit is sufficient to put the animal within a short time into deep anesthesia. This is less than half the dose that is required to anesthetize a normal rabbit. Furthermore, the nephrectomized rabbits thus anesthetized remained in a more or less comatose, paralyzed state until death, which did not occur earlier than in the control nephrectomized animal; in other words the animals remained in a state of anesthesia lasting sometimes two days and longer. Frequently the animals recovered slightly some hours after the injection, to sink soon again, however, into a deep stupor which lasted until death. The described effect was the same whether the above mentioned quantity of salt was given in one dose or was administered in fractions.

These facts demonstrate that elimination of the injected magnesium salt occurs mainly through the kidneys and that the elimination begins pretty soon after the injection. Hence when the kidneys are absent and practically no elimination takes place a smaller dose is sufficient to bring on the anesthesia, and it makes no difference whether the quantity is given at once or in small doses at varying intervals. Furthermore, the anesthesia is long lasting and continuous, as the salt cannot leave the body.