Anesthesia, << an uhs THEE zhuh, >> is the loss of sensation—particularly that of pain—in all or part of the body. Drugs called anesthetics are used to produce temporary anesthesia for medical purposes. Anesthesia is also produced by hypnosis and by acupuncture—the insertion of needles at certain points on the body. Some injuries and diseases, especially those of the nervous system, also can lead to loss of sensation.
Without anesthesia, doctors could not perform most surgical operations. Because an anesthetic makes the patient insensitive to pain, it greatly reduces the physical shock and emotional stress of the operation. The use of anesthetics gives the surgeon time to perform complicated operations safely.
General anesthesia
is the loss of feeling in the entire body. It is accompanied by unconsciousness. General anesthetics are inhaled, injected, or swallowed. The blood carries them to the brain, where they block pain impulses in the nervous system. Common general anesthetics include enflurane, halothane, isoflurane, nitrous oxide (laughing gas), and thiopental (sodium pentothal).
A person under general anesthesia shows various signs that indicate the depth of unconsciousness. In deep levels of anesthesia, the patient loses such reflex actions as coughing, and heart and respiration rates slow. In surgery, the patient’s reactions to the anesthetic and to the stress of the operation are monitored by the anesthetist to maintain a safe level of anesthesia.
Local anesthesia
involves the loss of pain sensation in only a part of the body. The individual remains conscious. Local anesthetics may be applied to body surfaces or injected around nerves. Physicians often use them when they operate on the eyes, nose, mouth, or skin. Dentists also use local anesthetics during painful procedures. Common local anesthetics include lidocaine, tetracaine, and procainelike drugs. These drugs also may be used to treat pain associated with injuries or diseases.
One type of local anesthesia, called regional nerve block, involves injecting an anesthetic around large nerves. With this technique, only the pain impulses from a particular region of the body are blocked. Spinal anesthesia occurs when the anesthetic is injected into the fluid within the coverings of the spinal cord. Peridural anesthesia is caused by injecting the anesthetic into the space just outside the covering of the spinal cord. When this is done at the lower end of the spine, it is called caudal anesthesia. Both spinal and peridural anesthesia render the lower parts of the body insensitive to pain, but the patient remains conscious. They are commonly used during childbirth and for surgery on the legs.
History.
Before the discovery of an effective anesthetic, the great pain and shock of operations severely limited the usefulness of surgery. In 1800, Humphry Davy, a British chemist, suggested that nitrous oxide be used as an anesthetic. However, no one tried this until 1844, when Horace Wells, an American dentist, used it on himself while having a tooth pulled.
In 1842, Crawford W. Long, a Georgia doctor, performed an operation after he had his patient breathe ether vapor until he was unconscious. In 1845, Long used ether for the first time in delivering a child. He did not publish the facts of his discoveries until 1849, by which time credit for the discovery of ether anesthesia had been given to W. T. G. Morton, a Boston dentist. At the recommendation of Charles T. Jackson, a Boston chemist, Morton used ether during a tooth extraction in the mid-1840’s. In 1846, he administered ether during a surgical operation at Massachusetts General Hospital. In 1847 and 1848, Sir James Y. Simpson, a Scottish physician, used chloroform to ease the pain of childbirth. Queen Victoria was one of the first women to be anesthetized during childbirth. The use of local anesthetics did not begin until the mid-1880’s.
During the early 1930’s, medical schools began offering formal training in anesthesia. Over the following decade, the study of anesthesia and the administration of anesthetics was recognized as a separate medical specialty called anesthesiology.
