Surgery Today - Anesthetics and how they are used

Anesthesia is a word derived from ancient Greek, meaning “without perception,” or a loss of sensation. During a major or minor operation, as in having a tooth extracted by a dentist, it is helpful to both the patient and the physician if there is a lack of sensation during the procedure. But eliminating pain isn't the only consideration in the choice of anesthetic and other drugs used in conjunction with it. The age of the patient, chronic ailments, the site of the operation, and the emotional status of the patient are among factors considered. If a patient has undergone surgery previously and had an adverse effect from a particular kind of anesthesia, this information would have an important influence on the choice of an alternative type of anesthetic.

For many types of surgery, the kind of anesthetic chosen may be the result of an agreement among the surgeon, the patient, and the anesthetist. Some patients, given a choice, would prefer to remain conscious during an appendectomy or hernia repair; others would rather not. The surgeon frequently recommends the use of a general anesthetic because the procedure may require more time than the patient can be comfortable with in an operating room situation. Therefore, patients should realize that when a surgeon recommends a general anesthetic for an operation in which a local or spinal anesthetic might be adequate, it is for their own welfare.

General Anesthetics

General anesthetics are those that produce “sleep,” or unconsciousness, along with analgesia , or absence of pain. They also cause a kind of amnesia in that the patient remembers nothing that occurs during the period in which the anesthetic is effective. At the same time, general anesthetics produce a certain loss of muscle tone and reflex action. A general anesthetic, however, should not interfere significantly with such normal bodily functions as respiration and circulation, nor should it produce permanent damage to body tissues.

How They Work

General anesthetics cause the patient to fall into a kind of sleep state by depressing the central nervous system, an effect that is reversible and lasts only until the drug has been eliminated by the body tissues. The general anesthetic reaches the central nervous system rather quickly because it is introduced directly or indirectly into the bloodstream. The use of a gas to produce anesthesia is an indirect method of producing unconsciousness.

A gas-type anesthetic, such as nitrous oxide or cyclopropane, can be delivered under compression from tanks or cylinders, or it may be stored in the operating room as a liquid that is converted to a vapor, like ether or halothane. The compressed-gas anesthetics are administered with the help of an anesthetic machine. The liquid forms of gases may be dripped through a mask over the patient's face; or the liquid may be vaporized and directed to the patient by anesthetic equipment. Whether the source of the anesthetic is compressed gas or a volatile liquid, the purpose is the same: to get the anesthetic into the patient's lungs. There the gas enters the bloodstream through the walls of the blood vessels of the tiny sacs that make up the lungs.

Kinds of General Anesthetics

Nearly a dozen different kinds of gases are available as general anesthetics. Each has certain advantages and disadvantages and interacts differently with other drugs used by the patient. The effects of each on chronic diseases of the patient must be weighed. Some gases induce anesthesia more rapidly than others; some are tolerated better by patients. These are among the many factors that can determine which gas or mixture of gases might be selected by the anesthetist for a particular surgical procedure.

Intravenous Anesthetics

Not all general anesthetics come in the form of compressed gases or volatile liquids. Several commonly used general anesthetics are administered intravenously, by injection into the bloodstream. The group includes barbiturates, such as thiopental, and narcotics, such as morphine. Ketamine is a general anesthetic drug that can be injected into the muscles as well as into the bloodstream. The intravenous anesthetics may be used instead of the gaseous general anesthetics or in combination with them. Thiopental is often administered to a patient first, to bring on sleep quickly, after which an inhaled general anesthetic is applied. Like the gaseous general anesthetics, each of the injected general anesthetics has its own peculiarities and may have different effects on different individuals. The rate of recovery from thiopental anesthesia varies according to the ability of a patient's body tissue to eliminate the drug; narcotics can affect the patient's respiration; ketamine may produce hallucinations in some patients.

Regional Anesthetics

Regional anesthetics include local anesthetics and spinal anesthetics . They are more likely to be used than general anesthetics when the patient is ambulatory and the surgery involves removal of moles or cysts, plastic surgery, certain eye, ear, nose, and throat procedures, and certain operations such as hernia repair that generally are uncomplicated. Regional anesthetics also may be recommended by the surgeon for operations to correct disorders in the arms or legs.

The surgical procedure may require that the patient remain conscious so he can follow instructions of the surgeon in manipulating muscles or bones to test the function of a body part being repaired. In such cases, a regional anesthetic would be preferred; a regional also would be advised for a patient with severe heart or lung disease that might be complicated by the effects of a general anesthetic. A restless child, on the other hand, might be given a general anesthetic for a relatively minor operation, because the youngster would not be likely to remain motionless for the duration of the operation.

Topical Anesthetics

Regional anesthetics generally are administered by infiltration of a drug into the tissues involved or into the nerve trunks leading into the area of incision. A simple kind of regional anesthesia is the topical application of a substance to a sensitive membrane of a body organ. For example, the eye drops applied by an ophthalmologist may anesthetize a patient's eyes to make it easier for him to examine them. Topical anesthetics are not very effective when applied to the skin, which forms a tough barrier against most invasive substances, but they can effectively anesthetize the inner surfaces of the mouth, nose, throat, and other inner body surfaces. The anesthetic might be administered by sprays, gargles, or by direct application. Topical anesthetics commonly are used to prepare the throat and upper lung passages for examination with medical instruments.

Local Anesthetics

Local anesthetics, which are similar to those used by the dentist, are usually injected via a hypodermic needle into the tissues surrounding the area to be operated on. The injection of an anesthetic into the tissue area sometimes is referred to as a field block . A variation of this technique is the nerve or plexus block , in which a hypodermic needle is used to inject the drug into the region of one or more key nerve trunks leading to the site of the incision. Local anesthetics are not recommended by most surgeons if there is an inflammation or infection of the tissues around the surgery site. The drugs used for local anesthetics can lower the patient's resistance to the infection while at the same time the inflammation may reduce the effectiveness of the drug as a pain-killer.

Intravenous Administration

Sometimes a regional anesthetic is administered intravenously by injecting it into a vein that runs through the site of the surgery. The drug is confined to the area, such as an arm or leg, by applying a tourniquet about the limb. Because of the possible dangers in suddenly releasing a potent anesthetic drug into the general bloodstream after the operation is ended, the tourniquet is intermittently tightened and released to slow the flow to a mere trickle. A sudden release also would quickly end the pain-killing effect in the area of the incision.

Spinal Anesthetics

Spinal anesthesia is similar to a nerve or plexus block method of eliminating pain sensation in a region of the body, except that the nerves receive the drug at the point where they leave the spinal cord. The drugs may be the same as those used as local anesthetics. They are injected either by hypodermic needle or by catheter into tissues surrounding the spinal cord. Although there are several variations of spinal anesthesia—each involving the precise layer of tissue or space around the spinal cord which is the immediate target area of the injection—for all practical purposes the objective is the same. They are all intended to produce a lack of sensation in the spinal nerves along with a loss of motor function so there will be no movement of the body area to be operated on during surgery.

The spinal anesthetic may affect not only the targeted nerve system but neighboring spinal nerves as well, generally all the spinal nerves below the point of drug injection. For its purposes, spinal anesthesia can be a highly effective alternative to a general anesthetic. However, side effects are not uncommon. Severe headache is one of the most frequent complaints of patients. Temporary adverse effects can occur after use of other regional anesthetics as well and may be owing in part to individual allergic reactions to the drug used.