—These are also mechanical means of controlling hemorrhage, but deserve to be grouped by themselves. Ligation of vessels may be preliminary or may be performed as needed during an operation.
By a preliminary ligature is meant taking such precaution as tying the carotid before operations on the face, the brain, or the femoral artery before amputation at the hip. There is also the method of temporary ligation of vessels by the application of a ligature which should not be drawn too tightly, but simply serve the purpose of gentle constriction for the half-hour or so during which it may be needed, after which the vessel is promptly released. If this ligature has not been too tightly applied the vessel walls will not have been injured and circulation is restored. Crile has effected the same purpose with the carotids by a small clamp whose pressure may be regulated by a thumb-screw.
Ligation of large trunks is made for the purpose of influencing nutrition by diminishing blood supply, as when the femoral is tied for elephantiasis of the leg, or the carotid is tied or excised, as suggested by Dawbarn, to cut off the blood supply from cancer of the face or neck.
Ligatures are usually made of absorbable material, such as catgut, chromicized or not, as may be desired, or of silk, which disappears after a time, but which is not regarded as absorbable. For special purposes other material has been used at times, such as strips of ox aorta. The surgeon has his choice of these, whether he intends to ligate the end of an artery or tie a vessel in its continuity. For the latter purpose the ligature is threaded into an artery needle, or a specially devised curved forceps known as the “Cleveland” needle. When tying the exposed end of a bleeding vessel it is desirable to tie near the cut end, so as not to leave tissue which should be absorbed, and for the same reason to not include unnecessary tissue. One of the forms of knot similar to the “reef” knot, which will not slip, should be used. Silk has the advantage over catgut in that a knot tied with it will rarely become loose, whereas catgut knots, unless carefully tied, will occasionally slip. The ligature knots should be left as short as is consistent with protection against slipping.
Fate of Ligatures.
—Silk or celluloid thread are the most unabsorbable of ligature materials ordinarily used. Even these usually disappear after the lapse of time. Absorbable ligatures of catgut disappear after a few days or weeks, according to the method of their preparation. Absorption is practically a matter of phagocytosis, the end of the vessel or tissue beyond the ligature disappearing with the latter by the process of tissue digestion.
When vessels of large size are ligated the blood supply is taken up by the collateral circulation. On the possibility or practicability of the latter will depend the success of such operations as ligation of large trunks for the cure of aneurysm. Should the collateral supply prove insufficient, gangrene, beginning at the tip of an extremity, is an assured fact.
The effects of the ligature on the vessel wall will depend upon the security with which it is tied. The damage done to the inner and middle coats by a ligature tied for permanent purposes is usually sufficient to rupture them, after which they roll up inside the outer coat, while the blood contained in that part of the vessel coagulates, the clot extending to the first vessels above and below. This quickly organizes, becomes infiltrated with cells, and brings about the complete obliteration of that part of the vessel and its transformation into a fibrous cord. This can only occur, however, when asepsis has prevailed. Should the ligature prove septic the patient is exposed to two dangers: that of secondary hemorrhage by ulceration and breaking down of the clot instead of organization, and the ordinary dangers of septic infection.
There are circumstances under which it may be well to modify the ordinary methods of ligation and not to tie knots too tightly—i. e., when the vessels are greatly weakened by extensive disease, or so stiffened by calcareous degeneration as to cause them to snap under rough handling. It has been suggested to use pieces of ox aorta to prevent these accidents.
The dangers of secondary hemorrhage pertain mostly to septic conditions. In an absolutely aseptic wound, properly cared for, secondary hemorrhage is almost impossible, but as soon as germ activity begins lymph barriers are broken down, tissues softened, and weakened vascular walls may give way.