Pressing out too much of the solution at one time causes a burning sensation and should therefore be avoided as the only pain should be that of the initial prick of the needle. Care, however, should be taken to inject just sufficient of the solution to penetrate beyond the zone of operation laterally, to insure sufficient space for the insertion of sutures into anesthetized tissues. Only a small quantity of fluid is necessary in this procedure as it comes in direct contact with nerve terminals. By touching the injected line with the needle in several places along its length and inquiring of the patient if it is felt, we may make sure of the completeness of the anesthesia before making the incision which should begin and end inside the anesthetized area.
Subdermic Method. An appreciable area of skin and subcutaneous tissue may be incised by anesthetizing as previously described, together with depositing the fluid well under the skin, thus affecting many terminal nerve branches before they reach their final distribution in the skin, and widening the anesthetized area considerably.
This method is applicable to such work as the removal of small growths, and the deep incision of a carbuncle. Beneath the skin in the loose connective tissue the fluid is deposited and causes anesthesia by acting upon the nerves just before their emergence into the skin. The two methods may be combined. It is not possible to inject directly into thin skin or mucous membrane and it is therefore employed in such operations as circumcision, where the nerve terminals must be anesthetized by the diffusion of the anesthetic from its position under the skin. A little time should be allowed before beginning the operation to permit of the diffusion of the drug. This applies also to such operations as that for ingrown toe-nail where the deeper tissues down to the root of the matrix are involved.
Edemitization Method. This is the method of Schleich and it is to him that the credit must be given for a procedure which has done more to encourage the use of local anesthetics in operative surgery than any other. He employed weak solutions of cocaine and other local anesthetics in great volumes of water in order to gain the combined action of both drug and of pressure. The method is described under the heading of “Cocaine.” It was designed to obtain anesthesia with cocaine with the elimination of the toxic effects of the latter.
There are decided disadvantages to the filling up of the tissues with fluid; healing is delayed; relations are distorted and coaptation of the edges is difficult. This is probably the method of selection where an indefinite amount of manipulation is expected and where the length and depth of the incision may need to be augmented. A large quantity of a very weak solution is employed and the tissues in all directions are injected until visibly distended.
Nerve Blocking Method. By injecting a small quantity of a fairly strong anesthetic solution either directly into a nerve or beneath its sheath, the entire area supplied by it will be anesthetized. This method of nerve blocking may be spoken of as endoneural when the injection is made directly into the nerve trunk, and perineural when made into its sheath or immediately outside of the nerve. The injection of fluid around nerves too small to inject directly is also spoken of as perineural nerve blocking. (Hertzler).
DRUGS EMPLOYED
The essential qualities of a good local anesthetic are:
1. Reliability in producing anesthesia.