Chapter IX · LOCAL ANESTHESIA

Local anesthesia is a condition of insensibility brought about in a part of the body by the use of agents called local anesthetics. The person in whom the local anesthesia is produced does not lose consciousness as in general anesthesia, the part alone being made insensible.

There are many agents which, when applied to a part, by one means or another, cause that part to become insensible to pain, but for the podiatrist the following agents are best calculated to serve his purposes: cocaine, novocaine, alypin and urea hydrochloride, ethyl chloride, ethyl bromide, carbon dioxide snow, apothesine and ice. (See footnote page 148.)

Cocaine is an alkaloid extracted from coca leaves. These latter are not to be confused with cocoa, the seed of the chocolate tree. When cocaine is treated with hydrochloric acid, hydrochloride of cocaine is produced which occurs in a white crystalline powder, soluble in water and alcohol. When injected into the skin, or applied to an open wound, it acts as a paralyzant to the vasodilators and as a stimulant to the vasoconstrictors. When applying this drug, a tourniquet should be used wherever possible, so as to prevent absorption. This precaution is essential, as cocaine⁠[2] is very toxic, and even small quantities may produce bad effects in some persons. There are cases on record in which ¹⁄₁₀₀ of a grain of this drug has produced all the symptoms of toxemia, whereas there are persons who can stand doses up to one grain. It is therefore essential to use judgment and care in administering a drug which on account of the idiosyncrasies of some people, is likely, even in minute doses, to produce serious, if not fatal symptoms.

In podiatry, a ¹⁄₂% solution is strong enough for general use, provided that time enough is allowed for the drug to be diffused. For an ordinary ingrown toe nail, two cubic centimeters of the above solution is usually sufficient to produce anesthesia of the part.

Novocaine is a synthetic preparation and occurs in colorless needles. It can be heated to 120 degrees Centigrade, without undergoing decomposition, which is not the case with cocaine hydrochloride. Although not quite as efficient as an anesthetic, novocaine is only ¹⁄₇ as toxic as cocaine and therefore can be used with greater safety and podiatrists generally have abandoned cocaine for novocaine. It has a slightly irritating action while being injected, but on the whole it is preferable to cocaine for podiatry practice. Physiologically, it has the same action as cocaine, and is indicated wherever the latter drug is used. It is usually injected in one per cent. solutions.

Alypin occurs as a crystalline powder. It is a most efficient anesthetic and because of its non-toxic action, it is to be preferred in cases in which there is a fear of toxemia. Maximilian Stern, M.D., Professor of Surgery at the First Institute of Podiatry, has used this drug extensively for producing local anesthesia, and his results have been very satisfactory. For use in podiatry, a ¹⁄₄ to ¹⁄₈ per cent. solution is often sufficient. It may be used freely in ¹⁄₄ per cent. strength without danger of toxemia. When injected, it produces no anemia, and consequently there is no danger of subsequent hemorrhage, such as might accompany the use of either cocaine or novocaine.

Quinine and urea hydrochloride is one of the quinine salts, consisting of one molecule of quinine hydrochloride and one molecule of urea. It has no toxic action when injected into the tissues, but it retards healing, and scar tissue forms over operated areas where it has been used. Many operators prefer this drug on account of its non-toxic action when used in large quantities, despite the likelihood of a scar and slow union. In parts of the body where contraction of the tissues is a desirable after-effect (such as would be the case in hemorrhoids), quinine and urea hydrochloride is to be preferred over other local anesthetics. David H. Levy, M.D., a well known surgeon of New York City, prefers it to all other local anesthetics.

Ethyl chloride and ethyl bromide are clear volatile liquids, and upon their rapid evaporation depend their anesthetic qualities. When a substance evaporates rapidly, it extracts the heat from surrounding bodies in doing so, and, consequently, when such a substance is applied to the skin, it soon extracts the heat from the part and with the local anemia thus produced, sensation is lost. Ethyl chloride and ethyl bromide are manufactured in tubes so arranged as to eject a fine stream of the liquid. When this stream comes in contact with the skin, evaporation is rapid and gradually the part becomes numb; continued, it becomes frozen. This method is not as efficient as the hypodermic injection because the anesthesia is not so lasting, moreover, the reaction is severe and painful. Otto Sjogren and Fred Schmitt, practitioners of known repute, have entirely discarded both of these drugs from their list of local anesthetics, for reasons above mentioned.

Carbon dioxide snow is prepared by allowing liquified carbon dioxide gas to slowly escape from its container into a glove finger, where it solidifies into a mass, assuming the shape and form of the receptacle; it is called the carbon dioxide pencil. When this mass or pencil is applied to a part, it extracts the heat and anesthetizes by freezing. The dangers attending the use of the carbon dioxide pencil are the same as with ethyl chloride or ethyl bromide and, due to its extremely low temperature, there is danger of causing death of the tissues and of producing conditions giving rise to subsequent ulcerations that are slow to heal. As an anesthetic, it is not advised for podiatry.

Technic of Producing Local Anesthesia. There are three methods of producing local anesthesia: (1) the hypodermatic method: (2) the pressure method: (3) freezing.

The freezing method is of no great value to the podiatrist, and having been already briefly described, further comment is deemed unnecessary.

The pressure method of producing local anesthesia is new, and although extensively employed in the practice of dentistry, podiatry offers but little opportunity for its free use. It is necessary to have an exposed nerve, such as is found in the cavities of painful teeth, or an open wound into which the drug can be absorbed, before this method can be used. In cases of ingrown toe nail, in which the groove is lacerated, either by the patient or by the nail itself, pressure anesthesia is often efficacious. Small pellets containing cocaine or novocaine, with adrenalin, are put on the market for this purpose. One of these pellets is placed in the nail groove, and a drop of alcohol is made to fall on it. The contents of the pellet are promptly dissolved by the alcohol, whereupon the operator places his thumb over the nail groove between the nail and the nail flap and exerts downward pressure. This forces the dissolved fluid into the tissues, where it acts the same as if it were injected. This procedure is painful for just a moment while the pressure is being applied, but the pain soon ceases and nerve sensibility is lost.

The most generally used method of applying local anesthetics is by means of the hypodermic syringe and is called the [3]⁠hypodermatic method. This is preferable to all other forms of inducing local insensibility, and if the technic is mastered, operations will be painless with the exception of the initial prick of the needle.

The Hypodermic Syringe should be so constructed that it may be sterilized by boiling. There are many types of such instruments sold, and in making a selection, only those which will permit such boiling should be considered. The all-glass syringe or the glass and metal syringe with the metal piston are best, because the fluid contained therein is visible, thus preventing the injection of air. Needles should be of the rust-proof variety and for use in podiatry, they should be one-half or one inch long and have a twenty or twenty-two gauge lumen.

After the syringe has been sterilized, it should be adjusted and the fluid drawn into it after the needle is attached to the barrel. The entire instrument is then turned, needle up, and the air that may be in the barrel is expelled by pressure on the piston. When this is done, the syringe is ready for use.

If the needle is sterile, the only preparation necessary for the skin is to paint it with tincture of iodine, and then the injection of the anesthetic may be commenced. The area to be anesthetized is determined, and then at the most proximal portion, the skin is grasped between the thumb and forefinger of the left hand. The syringe should be held in the right hand with the barrel between the first and middle fingers, and the thumb on the piston. When the skin has been blanched by the pressure of the fingers of the left hand, the point of the needle, lumen downward, is thrust into the skin with a quick movement and immediately after, pressure is brought to bear upon the piston. As the fluid enters the tissues, it produces a blanched area which is called a wheal. As the wheal is formed, the needle is gradually moved forward in the derma until it is inserted as far as the base. It is then withdrawn, and a second injection is commenced, a little back of the distal end of the wheal. This second injection, being started in a part already anesthetized, will cause no pain. So the needle is gradually moved forward in the derma until the desired area has been covered.

When the deeper tissues are to be anesthetized, the needle may be directed at an angle to the surface, pressure being borne on the piston of the syringe as the needle gradually moves deeper into the flesh. It must be remembered that if the needle is re-inserted into an area that is already deadened, there will be no pain. The fluid should be ejected from the syringe slowly, which insures an even distribution of the drug, as well as comfort to the patient, while the anesthetic is being administered. Most drugs cause a burning sensation if injected too rapidly.

The most common lesion for which local anesthetics are used in podiatry is the ingrown toe nail, and to get good results in these cases, the technic must be followed in detail. After the derma has been anesthetized over the region of the nail root and groove, one deep injection should be made at the root, and vertically to the skin. This will insure loss of sensation when the root is cut and when the matrix at this point is curetted.

To prevent the absorption of toxic drugs into the system, some means should be devised to cut off the circulation during the operation. This is accomplished by the tourniquet, which is usually made of flexible, solid rubber, about one-sixteenth or one-eighth inch in diameter and about a foot long. When this band is tied around the base of the toe, and pulled tight, it cuts off the circulation. Tourniquets cannot be used when operating upon the foot proper, and in these cases it is necessary to be guarded in the use of toxic drugs.

After the use of cocaine⁠[4] or novocaine there is a reaction, and occasionally the pains produced by this reaction are severe. These pains may be alleviated to some extent by the use of wet dressings, but they last only for a short time so that it is often unnecessary to treat them. The patient should be warned of the reaction. The local anemia produced by the injection of these drugs is subsequently followed by hyperemia, and it is therefore necessary to guard against hemorrhage in cases in which free incisions have been made. Wounds should be packed, and proper bandages should be applied to prevent any such possibilities.