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general anesthesia[¦jen·rəl ‚an·əs′thē·zhə]
a state of artificial sleep accompanied by a complete or partial loss of consciousness and by total insensitivity to pain. The main purpose of anesthesia in clinical practice is to suppress the body’s reactions, especially pain, to surgery.
Inhalation methods, noninhalation methods (intravenous, intraintestinal, and others), and combined methods of anesthesia are distinguished. Combined anesthesia achieves insensitivity to pain by the successive application of various anesthetic agents and techniques. With the inhalation method, which is the principle one, preanesthesia (induction) is used to make the patient drowsy. Preanesthesia is usually carried out by intravenous injection of fast-acting, short-lasting pharmacological agents, usually barbiturates, droperidol, fentanyl, propanidid, or sodium hydroxybutyrate. Induction may also be accomplished using gases (cyclopropane and nitrous oxide) and vapors of liquid anesthetics (halothane and methoxyflurane). When gas or vapor is used, the patient inhales the anesthetic through a mask, which is connected to an anesthesia machine.
Basal anesthesia, as opposed to inductive anesthesia, is administered to the patient in the ward. An agent that induces a prolonged superficial anesthesia is first used. After being brought to the operating room, the patient can then be given more of the same drug or another method is employed to deepen the anesthesia. Muscle relaxants completely eliminate muscle contraction, permitting easy insertion of a tube into the trachea and induction of superficial anesthesia. Such a procedure averts the danger of overdose, even during extensive surgery. The patient’s electroencephalogram, pulse, and blood pressure are monitored to prevent a premature return to consciousness. Inhalation anesthesia is maintained at the appropriate level by means of vaporizers and dosimeters, special devices that permit precise regulation of the concentration of liquid or gaseous anesthetics.
The recovery from anesthesia is as critical as the induction and maintenance of anesthesia. When emerging from anesthesia, a patient’s reflexes are either partially restored immediately or they can remain insufficient for some time. Delayed recovery accounts for several complications in anesthesia that require anesthetists to continue observing the patient even after the completion of the operation.
T. M. DARBINIAN
The apparatus used for anesthesia is a gas-conducting system, connected to the patient’s respiratory tract. The gaseous mixture should contain an adequate concentration of oxygen and a minimum concentration of carbon dioxide. The apparatus should interfere with breathing as little as possible. Several anesthetic methods are classified according to the degree to which the patient’s breathing system is separated from the surrounding atmosphere: (1) the open method, involving inhalation through a vaporizer from the atmosphere and exhalation into the atmosphere; (2) the semiopen method, in which the inhaled mixture enters from compressed gas cylinders and is exhaled into the atmosphere; (3) the semiclosed method, in which the inhaled mixture enters from tanks and the exhaled mixture partly returns to the respiratory system of the apparatus (this mixture can be inhaled again as part of the gaseous anesthetic mixture) and partly escapes into the atmosphere; (4) the closed method, in which the inhaled gaseous anesthetic mixture enters from cylinders and the exhaled portion completely returns to the apparatus for reinhalation. These last two methods require the use of a carbon dioxide adsorbent. Each method has its own advantages and shortcomings. For example, pollution of the operating room atmosphere with anesthetic vapors and gases is minimal when the closed method is employed. Shortcomings of the closed method, however, include considerable resistance of the apparatus during the patient’s exhalation and the need to use a carbon dioxide adsorbent.
An anesthesia machine can be divided into at least three functional units: a vaporizer for the anesthetic, or the gas dosimeter; a breathing bag, or bellows; and gas-conducting hoses with valves. The breathing bag permits artificial ventilation of the lungs. An apparatus for electroanesthesia, the NEIP-1, has been developed in the USSR. With this device, anesthesia is achieved by applying an electric current to the brain. The advantages of this type of anesthesia are the quick induction of anesthesia, a short recovery period, and the relatively harmless nature of the side effects experienced by the internal organs.
V. V. SIGAEV
REFERENCESZhorov, I. S. Obshchee obezbolivanie, Moscow, 1964.
Spravochnik po anesteziologii i reanimatsii, 2nd ed. Moscow, 1970.
Rukovodstvo po anesteziologii. Moscow, 1973.