anesthesia(redirected from field block anesthesia)
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anesthesia (ănĭsthēˈzhə) [Gr.,=insensibility], loss of sensation, especially that of pain, induced by drugs, especially as a means of facilitating safe surgical procedures. Early modern medical anesthesia dates to experiments with nitrous oxide (laughing gas) by Sir Humphry Davy 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. Morton 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 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).
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