If moist gangrene supervenes, amputation must be performed without delay, and at a higher level.
Gangrene from Heat, Chemical Agents, and Cold.—Severe burns and scalds may be followed by necrosis of tissue. So long as the parts are kept absolutely dry—as, for example, by the picric acid method of treatment—the grossly damaged portions of tissue undergo dry gangrene; but when wet or oily dressings are applied and organisms gain access, moist gangrene follows.
Strong chemical agents, such as caustic potash, nitric or sulphuric acid, may also induce local tissue necrosis, the general appearances of the lesions produced being like those of severe burns. The resulting sloughs are slow to separate, and leave deep punched-out cavities which are long of healing.
Carbolic Gangrene.—Carbolic acid, even in comparatively weak solution, is liable to induce dry gangrene when applied as a fomentation to a finger, especially in women and children. Thrombosis occurs in the blood vessels of the part, which at first is pale and soft, but later becomes dark and leathery. On account of the anæsthetic action of carbolic acid, the onset of the process is painless, and the patient does not realise his danger. A line of demarcation soon forms, but the dead part separates very slowly.
Gangrene from Frost-bite.—It is difficult to draw the line between the third degree of chilblain and the milder forms of true frost-bite; the difference is merely one of degree. Frost-bite affects chiefly the toes and fingers—especially the great toe and the little finger—the ears, and the nose. In this country it is seldom seen except in members of the tramp class, who, in addition to being exposed to cold by sleeping in the open air, are ill-fed and generally debilitated. The condition usually manifests itself after the parts, having been subjected to extreme cold, are brought into warm surroundings. The first symptom is numbness in the part, followed by a sense of weight, tingling, and finally by complete loss of sensation. The part attacked becomes white and bleached-looking, feels icy cold, and is insensitive to touch. Either immediately, or, it may be, not for several days, it becomes discoloured and swollen, and finally contracts and shrivels. Above the dead area the limb may be the seat of excruciating pain. The dead portion is cast off, as in other forms of dry gangrene, by the formation of a line of demarcation.
To prevent the occurrence of gangrene from frost-bite it is necessary to avoid the sudden application of heat. The patient should be placed in a cold room, and the part rubbed with snow, or put in a cold bath, and have light friction applied to it. As the circulation is restored the general surroundings and the local applications are gradually made warmer. Elevation of the part, wrapping it in cotton wool, and removal to a warmer room, are then permissible, and stimulants and warm drinks may be given with caution. When by these means the occurrence of gangrene is averted, recovery ensues, its onset being indicated by the white parts assuming a livid red hue and becoming the seat of an acute burning sensation.
A condition known as Trench feet was widely prevalent amongst the troops in France during the European War. Although allied to frost-bite, cold appears to play a less important part in its causation than humidity and constriction of the limbs producing ischæmia of the feet. Changes were found in the endothelium of the blood vessels, the axis cylinders of nerves, and the muscles. The condition does not occur in civil life.
Diabetic Gangrene.—This form of gangrene is prone to occur in persons over fifty years of age who suffer from glycosuria. The arteries are often markedly diseased. In some cases the existence of the glycosuria is unsuspected before the onset of the gangrene, and it is only on examining the urine that the cause of the condition is discovered. The gangrenous process seldom begins as suddenly as that associated with embolism, and, like senile gangrene, which it may closely simulate in its early stages, it not infrequently begins after a slight injury to one of the toes. It but rarely, however, assumes the dry, shrivelling type, as a rule being attended with swelling, œdema, and dusky redness of the foot, and severe pain. According to Paget, the dead part remains warm longer than in other forms of senile gangrene; there is a greater tendency for patches of skin at some distance from the primary seat of disease to become gangrenous, and for the death of tissue to extend upwards in the subcutaneous planes, leaving the overlying skin unaffected. The low vitality of the tissues favours the growth of bacteria, and if these gain access, the gangrene assumes the characters of the moist type and spreads rapidly.
The rules for amputation are the same as those governing the treatment of senile gangrene, the level at which the limb is removed depending upon whether the gangrene is of the dry or moist type. The general treatment for diabetes must, of course, be employed whether amputation is performed or not. Paget recommended that the dietetic treatment should not be so rigid as in uncomplicated diabetes, and that opium should be given freely.
The prognosis even after amputation is unfavourable. In many cases the patient dies with symptoms of diabetic coma within a few days of the operation; or, if he survives this, he may eventually succumb to diabetes. In others there is sloughing of the flaps and death results from toxæmia. Occasionally the other limb becomes gangrenous. On the other hand, the glycosuria may diminish or may even disappear after amputation.