Anesthesia

Anesthesia is the loss of feeling or sensation. It may be accomplished without the loss of consciousness, or with partial or total loss of consciousness.

Anesthesiology is a branch of medical science that relates to anesthesia and anesthetics. The anesthetist is a specialized physician in charge of supervising and administering anesthesia in the course of a surgical operation. Depending on the type of operation and procedures used, there are two types of anesthesia: general anesthesia, which causes a loss of consciousness, and local anesthesia, where the anesthetic "freezes" the nerves in the area covered by the operation. In local anesthesia, the patient may be conscious during the course of the operation or given a sedative, a drug that induces sleep .

History of anesthesia

While the search for pain control during surgery dates back to the ancient world, it was not until 1846 that it went on record that a patient was successfully rendered unconscious during a surgical procedure. Performed in a Boston hospital, the operation used a gas called ether to anesthetize the patient while a neck tumor was removed. In Western medicine, the development of anesthesia has made possible complex operations like open heart surgery and organ transplants. Medical tests that would otherwise be impossible to perform are routinely carried out with the use of anesthesia.

Before the landmark discovery of ether as an anesthetic, patients who needed surgery for either illness or injury had to face the surgeon's knife with only the help of alcohol , opium, or other narcotics. Often a group of men held the patient down during the operation in case the narcotic or alcohol wore off before it was over. Under these conditions many patients died just from the pain of the operation.

Nitrous oxide

In 1776 Joseph Priestley, a British chemist, discovered the gas nitrous oxide. Another British chemist, Humphry Davy, proposed nitrous oxide as a means for pain-free surgery, but his views were dismissed by other physicians of the day. In the next century, Horace Wells, a Connecticut dentist, began to experiment with nitrous oxide, and in 1845 attempted to demonstrate its anesthetic qualities to a public audience. However, the patient woke before the operation was over and began to scream in pain. Because of this spectacle, it took another 20 years before nitrous oxide again gained attention. By 1870, nitrous oxide was a commonplace dental anesthetic.

Ether

The gas ether was discovered in 1540 and given its name in 1730. The gas was first successfully used by an American physician, Crawford W. Long, in an operation in 1842. The operation, however, was unrecorded, so official credit went instead to William Morton for his 1846 demonstration of an operation with the use of ether.

Chloroform

The credit for discovering the third major anesthetic of this period in medical history goes to James Young Simpson, a Scottish gynecologist and obstetrician. Simpson used ether in his practice but searched for an anesthetic that would make bearing children less painful for women. He tested several gases until he came upon chloroform in 1847 and began to use it on women in labor. Chloroform use, though, had higher risks than those associated with ether, and it called for greater skill from the physician. Neither ether nor chloroform are used in surgery today.

Emergence of anesthesiology

Anesthesiology as a medical specialty was slow to develop. By the end of the nineteenth century, ether, which was considered safer than chloroform, was administered by etherizers who had little medical experience, including students, new physicians, non-medical specialists, nurses, and caretakers. Eventually, nurses began to be used for this job, becoming the first anesthetists by the end of the nineteenth century.

While the practice of surgery began to make considerable progress by the turn of the century, anesthesiology lagged behind. In the twentieth century, though, the need for specialists in anesthesia was sparked by two world wars and advanced surgical techniques. To meet these demands, the American Society of Anesthetists was formed in 1931 and specialists were then certified by the American Board of Anesthesiology in 1937. By 1986, the Board certified 13,145 specialists—physicians and nurses, called nurse anesthetists—in the field of anesthesiology.

Types of anesthesia

Modern anesthesiology can be divided into two types, pharmacological and non-pharmacological. Pharmacological anesthesia uses a wide variety of anesthetic agents to obtain varying degrees of sedation and pain control. The anesthesia is administered orally, by injection, or with a gas mask for inhalation. Examples of nonpharmacological anesthesia are the use of breathing techniques during conscious childbirth (Lamaze method of natural childbirth) and the ancient art of Chinese acupuncture . Non-pharmacological anesthesia requires special skills on the part of its practitioners, and its effects are not as reliable as pharmacological techniques.

Pharmacological anesthesia is described as either general or local.

General anesthesia

There are three phases to general anesthesia. The anesthetist must first induce the state of unconsciousness (induction), keep the patient unconscious while the procedure is performed (maintenance), then allow the patient to emerge back into consciousness (emergence).

A drug commonly used to induce unconsciousness is thiopentone sodium . It is a barbiturate that produces unconsciousness within 30 seconds after being injected intravenously. Thiopentone does not reduce pain; it actually lowers the threshold of pain. It is used in the induction stage to bring about a quick state of unconsciousness before using other drugs to maintain the anesthetic condition during surgery.

Other agents used for the induction and maintenance of anesthesia are gases or volatile liquids such as nitrous oxide, halothane, enflurane, methoxyflurane and cyclopropane.

Nitrous oxide is still commonly used in dentistry , minor surgery, and major surgery when it is accompanied by other anesthetics. Though the gas has been used for many years, it is still uncertain how nitrous oxide accomplishes its anesthetic effect. Mixtures of oxygen and nitrous oxide appear to enhance its effect. Unlike other agents used today, it appears to have no toxic side effects on the body.

Halothane is a colorless liquid with a very low boiling point . Its use, though, may be connected to liver toxicity. Enflurane and methoxyflurane are also liquids that are useful as analgesics (pain relievers) and muscle relaxants , but they also may have undesirable side effects. Cyclopropane, which is an expensive and explosive gas used for rapid induction and quick recovery, has over the years been replaced with the use of halothane.

The anesthesiologist interviews the patient before the operation and examines his or her medical records to determine which of the many anesthetic agents available will be used. Cyclopropane or atropine may be given before the operation to relieve pain and anxiety . When a muscle relaxant is given for the surgical procedure, the anesthesiologist monitors the respiratory equipment to ensure the patient is breathing properly.

Administration of the anesthetic is usually accomplished by the insertion of a cannula (small tube) into a vein. Sometimes a gas anesthetic may be introduced through a mask. If a muscle relaxant is used, the patient may not be able to breathe on his own, and a breathing tube is passed into the windpipe (trachea). The tube then serves either to deliver the anesthetic gases or to ventilate (oxygenate) the lungs.

During the course of the surgery, the anesthesiologist maintains the level of anesthetic needed to keep up the patient's level of anesthesia to the necessary state of unawareness while monitoring vital functions, such as heart beat, breathing, and blood/gas exchange.

complications of general anesthesia. There are a number of possible complications that can occur under general anesthesia. They include loss of blood pressure , irregular heart beat, heart attack, vomiting and then inhaling the vomit into the lungs, coma , and death. Although mishaps do occur, the chance of a serious complication is extremely low. Avoidance of complications depends on a recognition of the condition of the patient before the operation, the choice of the appropriate anesthetic procedure, and the nature of the surgery itself.

Local anesthesia

Local anesthetics block pain in regions of the body without affecting other functions of the body or overall consciousness. They are used for medical examinations, diagnoses, minor surgical and dental procedures, and for relieving symptoms of minor distress, such as itching, toothaches, and hemorrhoids. They can be taken as creams, ointments, sprays, gels, or liquid; or they can be given by injection and in eye drops.

Some local anesthetics are benzocaine, bupivacaine, cocaine , lidocaine, procaine, and tetracaine. Some act rapidly and have a short duration of effect, while others may have a slow action and a short duration. They act by blocking nerve impulses from the immediate area to the higher pain centers. Regional anesthetics allow for pain control along a wider area of the body by blocking the action of a large nerve (nerve block). Sprays can be used on the throat and related areas for a bronchoscopy, and gels can be used for the urethra to numb the area for a catherization or cystoscopy.

Spinal anesthesia is used for surgery of the abdomen, lower back and legs. Spinal or epidural anesthesia is also used for surgery on the prostate gland and hip. A fine needle is inserted between two vertebrae in the lumbar (lower part) of the spine and the anesthetic flows into the fluid surrounding the spinal cord. The nerves absorb the anesthetic as they emerge from the spinal fluid. The area anesthetized is controlled by the location of the injection and the amount of absorption of the anesthetic by the spinal fluid.

complications of local anesthesia. It is possible to have adverse reactions to local anesthetics, such as dizziness, hypotension (low blood pressure), convulsions, and even death. These effects are rare but can occur if the dose is too high or if the drug has been absorbed too rapidly. A small percentage of patients (1-5%) may develop headaches with spinal anesthesia.

Theory of the mechanism of anesthesia

Although scientists are not sure exactly how anesthesia works, there are many theories that have been proposed. In addition, different anesthetics may have different mechanisms of action. One theory proposes a relationship between the solubility of the anesthetic agent into the fat cells of the body (lipid solubility) as determining the degree of its potency as an anesthetic agent. Since nerve cell membranes are highly lipid, the brain , with its high nerve cell content, soaks up the anesthetic. Not all lipid soluble substances, however, are anesthetics. Lipid solubility, therefore, is only a partial explanation of the anesthetic's mechanism.

Another feature of anesthetic absorption is the way it is passed from the lungs to other cells in the body. At first there is a quick transmission from the lungs to the rest of the body, but as an equilibrium is reached, the anesthetic begins to quickly pass out from the lungs. However, fat cells retain the anesthetic longer than other cells.

Studies have shown that some inhaled anesthetics are metabolized by the liver (hepatic metabolism ). Here is where the skill of the anesthetist is needed to control the amounts administered in order to avoid the problem of toxicity.

The future of anesthesia

Since World War II, many changes have taken place in anesthesiology. Important discoveries have been made with such volatile liquids as halothane and synthetic opiates. The technology of delivery systems has been greatly improved. But with all these changes, the basic goal of anesthesia has been the same—the control of a motionless surgical field in the patient. In the next 50 years it is possible that the goals of anesthesia will be widened. The role of anesthesia will broaden as newer surgical techniques develop in the area of organ transplants. Anesthesia may also be used in the future to treat acute infectious illness, mental disorders, and different types of heart conditions. There may be a wide range of new therapeutic applications for anesthesia.

Anesthesiologists compete strongly for research funds. Better trained anesthesiologists need to do research to gain further knowledge on the effects and mechanisms of anesthesia. Since understanding and controlling pain is the central problem of anesthesiology, it will be necessary to gain more knowledge about the mechanism of pain and pain control. New anesthetics, delivery, and monitoring systems will need to be developed to keep up with the pace of medical development as it moves closer to noninvasive surgical techniques.

See also Analgesia; Novocain.

Resources

books

Barash, Paul G., Bruce F. Cullen, and Robert K. Stoelting. Clinical Anesthesia. Philadelphia: Lippincott, 1992.

McKenry, Leda M. and Evelyn Salerno. Mosby's Pharmacology in Nursing. Philadelphia: Mosby, 1989.

Jordan P. Richman

KEY TERMS

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Chloroform

—A simple chlorinated hydrocarbon compound consisting of one carbon atom, one hydrogen atom, and three chlorine atoms. One of several early gases, along with ether and nitrous oxide, that opened the way for the successful pharmacological use of anesthesia.

Consciousness

—A mental state involving awareness of the self and the environment..

Halothane

—An important, current volatile liquid anesthetic.

Lipid solubility

—The ability of a drug to dissolve in fatty tissue.