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.
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 narcotic. 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, another gas still commonly used in dentistry, minor surgery, and some major surgery, was discovered in 1776 by British chemist Joseph Priestly. Another early anesthetic, chloroform, was discovered in 1847 by James Young Simpson. The Scottish gynecologist and obstetrician was searching for an anesthetic that would make bearing children less painful for women. 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.
Anesthesiology as a medical specialty was slow to develop. By the end of the 19th century, ether 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 19th century.
While the practice of surgery began to make considerable progress by the turn of the century, anesthesiology lagged behind. In the 20th 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.
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 non-pharmacological
Pharmacological anesthesia is described as either general or local. 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).
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.
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 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 which surrounds the spinal cord. The nerves absorb the anesthetic as they emerge from the spinal fluid. The anesthetized area is controlled by the location of the injection and the amount of absorption by the spinal fluid.
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.
Babies born to mothers who have been administered anethetics during labor and delivery often show anesthetic effects for a period of time after birth. Medication given to women immediately before delivery passes through the placenta to the baby. While the effects of the anesthetic wear off relatively quickly for the mother, it takes the baby's immature system longer to process it out of the body. Affected babies frequently appear lethargic and unresponsive for longer periods of time after birth than babies delivered without maternal medication. While use of anesthetics by the mother is not believed to have any permanent impact on the baby, many pediatricians contend difficulties in breastfeeding and maternal bonding can result from babies' unresponsive behavior in the early days of life.
Special care also must be taken when administering anesthetics to children. Allergic or anaphylactic reactions to a particular medication are difficult to predict, particularly in younger patients who have experienced fewer medical procedures.
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 fifty 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.
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Mckenry, Leda M., and Evelyn Salerno. Mosby's Pharmacology in Nursing. Philadelphia: Mosby, 1989.