anesthesia

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anesthesia

(ănĭsthē`zhə) [Gr.,=insensibility], loss of sensation, especially that of painpain,
unpleasant or hurtful sensation resulting from stimulation of nerve endings. The stimulus is carried by nerve fibers to the spinal cord and then to the brain, where the nerve impulse is interpreted as pain.
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, induced by drugs, especially as a means of facilitating safe surgical procedures. Early modern medical anesthesia dates to experiments with nitrous oxidenitrous oxide
or nitrogen (I) oxide,
chemical compound, N2O, a colorless gas with a sweetish taste and odor. Its density is 1.977 grams per liter at STP. It is soluble in water, alcohol, ether, and other solvents.
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 (laughing gas) by Sir Humphry DavyDavy, Sir Humphry,
1778–1829, English chemist and physicist. The son of a woodcarver, he received his early education at Truro and was apprenticed (1795) to a surgeon-apothecary at Penzance.
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 of England and the dentist Horace Wells of the United States. Ether came into general use as an anesthetic after a demonstration at the Massachusetts General Hospital in Boston by William T. G. MortonMorton, William Thomas Green,
1819–68, American dentist and physician, b. Charlton, Mass., studied at Baltimore College of Dental Surgery. He practiced dentistry in Boston, for a time with Horace Wells, whose unsuccessful demonstration of nitrous oxide, or laughing gas, he
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 in 1846.

General anesthetics, administered by inhalation or intravenous injection, cause unconsciousness as well as insensibility to pain, and are used for major surgical procedures. In the past, ether was the most commonly used general anesthetic. Today, safer anesthetics include Halothane and Isoflurane, both of which are administered through inhalation. Short-acting anesthetic agents, such as pentothal, Diprivan, and Midazolam, are generally given through intravenous or intramuscular routes. Inhaled nitrous oxide is used for light anesthesia in minor surgical procedures and in dentistry. Ultra-short-acting analgesics can also be given intranasally for pre-medication prior to the induction of general anesthesia. Anesthetics such as Brevital may be administered rectally, primarily among children.

Local anesthetics affect sensation only in the region where they are injected, and are used regularly in dentistry and minor surgery. Spinal and epidural anesthesia involves the injection of an anesthetic agent into a space adjacent to the spinal cord, a technique frequently employed for surgical procedures below the waist (e.g., obstetrics) where total unconsciousness is not necessary. Such anesthetics are known as regional blocks. Muscle relaxants may be used in conjunction with general anesthetics, particularly to reduce the amount of anesthetic required. Body temperatures are generally lowered in conjunction with the use of anesthetics in heart and brain surgery, reducing the body's metabolic rate so that cells are not damaged by the lack of circulating blood and reduced oxygenation. Several forms of anesthesia may be used in combination. Safer and more efficient anesthetics are constantly researched, in the hopes of perfecting new ways of combining and administering them.

See also acupunctureacupuncture
, technique of traditional Chinese medicine, in which a number of very fine metal needles are inserted into the skin at specially designated points. For thousands of years acupuncture has been used, along with herbal medicine, for pain relief and treatment of various
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, analgesicanalgesic
, any of a diverse group of drugs used to relieve pain. Analgesic drugs include the nonsteroidal anti-inflammatory drugs (NSAIDs) such as the salicylates, acetaminophen, narcotic drugs such as morphine, and synthetic drugs with morphinelike action such as meperidine
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, anesthesiologyanesthesiology
, branch of medicine concerned primarily with procedures for rendering patients insensitive to pain, and for supporting life systems under the strains of anesthesia and surgery.
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, and surgerysurgery,
branch of medicine concerned with the diagnosis and treatment of injuries and the excision and repair of pathological conditions by means of operative procedures (see also anesthesia; medicine; radiology).
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.

Bibliography

See J. Rupreht et al., ed., Anesthesia: Essays on Its History (1985); J. Tolmie and A. Birch, Anesthesia for the Uninterested (2d ed. 1986); J. M. Fenster, Ether Day: The Strange Tale of America's Greatest Medical Discovery and the Haunted Men Who Made It (2001).

Anesthesia

 

the artificial removal of sensitivity to pain, used during surgical operations and during other diagnostic and treatment procedures. The study of anesthetic techniques is the principal concern of anesthesiology.

Analgesics in the form of medicinal herbs have been known from earliest antiquity, as have been the simplest methods of achieving anesthesia. In the 19th century morphine was widely used for anesthesia. Local anesthesia is distinguished from general anesthesia. In local anesthesia, the receptor nerve endings and the nerve pathways that carry impulses from the peripheral to the central nervous systems are blocked. In general anesthesia, activity is depressed in the cerebral nerve centers that perceive pain.

Several methods for achieving local anesthesia are used. A 0.25-percent solution of novocaine can be injected by the creeping infiltration method, which was developed by A. V. Vishnevskii. In conduction anesthesia, the anesthetic is injected directly into the nerve trunk. In cerebrospinal anesthesia, the anesthetic is injected into the cerebrospinal canal, and in epidural anesthesia, into the epidural space. Ethyl chloride or cocaine are applied in topical anesthesia to the surface of the organ or tissue.

Other methods for achieving local anesthesia are also used. For methods of general anesthesia, see, GENERAL.

T. M. DARBINIAN

anesthesia

[‚an·əs′thēzh·ə]
(physiology)
Insensibility, general or local, induced by anesthetic agents.
Loss of sensation, of neurogenic or psychogenic origin.

anaesthesia

(US), anesthesia
1. local or general loss of bodily sensation, esp of touch, as the result of nerve damage or other abnormality
2. loss of sensation, esp of pain, induced by drugs: called general anaesthesia when consciousness is lost and local anaesthesia when only a specific area of the body is involved
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