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ANAESTHESIA
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ANAESTHESIA and ANAESTHETICS (Gr. avataOnvla, from av- privative, and aivOnou, sensation), terms used in See also:medicine to describe a See also:state of See also:local or See also:general insensibility to See also:external impressions, and the substances used for inducing this state. In diseases of the See also:brain or See also:spinal See also:cord anaesthesia is an occasional symptom, but in such cases it is usually limited in extent, involving a See also:limb or a definite See also:area of the See also:body's See also:surface. See also:Complete anaesthesia occurs in a state of See also:catalepsy or trance—conditions associated with no definite See also:lesion of the See also:nervous See also:system.
The artificial See also:induction of anaesthesia has come to occupy a foremost See also:place in See also:modern medicine, but there is abundant See also:evidence to show that it is a practice of See also:great antiquity. Besides the mention by See also:Homer of the anaesthetic effects of nepenthe, and the reference by See also:Herodotus to the practice of the Scythians of inhaling the vapours of a certain See also:kind of See also:hemp to produce See also:intoxication, the employment of anaesthetics in See also:surgery by the use of mandragora is particularly alluded to by Dioscorides and See also:Pliny. It also appears, from an old See also:Chinese See also:manuscript laid before the See also:French See also:Academy by Stanislas See also:Julien, that a physician named Hoa-tho, who lived in the 3rd See also:century, gave his patients a preparation of hemp, whereby they were rendered insensible during the performance of surgical operations. Mandragora was extensively used as an anaesthetic by See also:Hugo de See also:Lucca, who practised in the 13th century. The soporific effects of See also:mandrake are alluded to by See also:Shakespeare, who also makes frequent mention of anaesthetizing See also:draughts, the See also:composition of which is not specified.
In the Medical See also:Gazette, vol. xii. p. 515, Dr See also:Sylvester, quoting from a See also:German See also:work by Meissner, published in 1782, mentions the See also:case of See also:Augustus, See also: In 'Soo, See also:Sir See also:Humphry See also:Davy, experimenting on nitrous See also:oxide (the so-called " laughing See also:gas "), discovered its anaesthetic properties, and described the effects it had on himself when inhaled with the view of relieving local See also:pain. He suggested its employment in surgery in the following words:—" As nitrous oxide, in its extensive operation, seems capable of destroying See also:physical pain, it may probably be used with See also:advantage in surgical operations in which no great effusion of See also:blood takes place." His See also:suggestion, however, remained unheeded for nearly See also:half a century. The inhalation of sulphuric See also:ether for the See also:relief of See also:asthma and other See also:lung affections had been employed by Dr See also:Pearson of See also:Birmingham as See also:early as 1785; and in 1805 Dr J. C. See also:Warren of See also:Boston, U.S.A., used this treatment in the later stages of pulmonary See also:consumption.
In 1818 See also:Faraday showed that the inhalation of the vapour of ether produced anaesthetic effects similar to those of nitrous oxide; and this See also:property of ether was also shown by the See also:American physicians, See also: See also:Morton, a dentist of Boston, employed the vapour of ether to procure general anaesthesia in a case of tooth-extraction, and thereafter administered it in cases requiring surgical operation with complete success. This great achievement marked a new era in surgery. Operations were performed in See also:America in numerous instances under ether in-halation, the result being only to establish more firmly its value as a successful anaesthetic. The See also:news of the See also:discovery reached See also:England on the 17th of December 1846. On the 19th of December Mr See also:Robinson, a dentist in See also:London, and on the 21st See also:Robert See also:Liston, the eminent surgeon, operated on patients anaesthetized by ether; and the practice soon became general both in Great See also:Britain and on the See also:continent.
Sir James See also:Simpson was the first to apply anaesthesia by ether to midwifery practice; this he did in 1847, and found that the pains of labour could be abolished without interference with uterine contractions or injury to the See also:child. On the 8th of See also: It, however, remained the See also:drug that was chiefly used till Dr J. T. See also:Clover (1825–1882) of London introduced his regulating ether-inhaler in 1876, embodying a new principle—that of limiting the quantity of See also:air during etherization and regulating the strength of the vapour.
During the intervening See also:period, as the results of the labours of John See also:Snow, Sir See also:Benjamin See also: When about to be used, it is allowed to See also:escape into a large See also:rubber bag, connected with a closely-fitting See also:face-piece, which covers up the See also:nose and mouth, and allows of See also:inspiration only from the bag of gas, expiration being into the air. When thus given the patient is exposed to a certain degree of asphyxia. This asphyxia is not only not necessary but is harmful, and may be obviated by giving oxygen in small amounts simultaneously by means of Hewett's regulating stopcock. This drug is used chiefly for dental operations, and for See also:minor surgery where See also:absolute See also:muscular relaxation is not required. When mixed with oxygen, it can be given if necessary for an See also:hour orlonger. It has an induction period of a few breaths only, and the recovery is as a See also:rule unaccompanied by excitement or See also:nausea. It is also used as a preliminary to ether; the gas is given till unconsciousness is reached, the unpleasant See also:taste of the ether being thus avoided and the induction period shortened. The mortality from nitrous oxide is small, and from the gas and oxygen in See also:expert hands nil. (2) Ethyl chloride, C2H5C1, a colourless liquid of a pleasant odour, boiling at 12.5° C. It 1S used in the same class of operations as the last anaesthetic. It is best given in an apparatus that consists of a See also:mask closely adapted to the face, and a rubber bag of small capacity, with which is connected the See also:bottle containing the ethyl chloride. The vapour supplied from the bottle is breathed backwards and forwards from the bag, fresh air being admitted in small quantities only. The period of induction is shorter than in the case of nitrous oxide, the patient losing consciousness in two or three breaths; the See also:stage of recovery is not so uniformly pleasant, headache, nausea and vomiting occurring not infrequently. It is difficult at present to estimate the mortality, as it has only recently come into general use, but it seems to occupy an intermediate position between ether and chloroform. (3) Ether, or ethyl oxide, (C2H5)20, a colourless, volatile liquid, boiling at 36.5° C. It has a pungent odour. It is best administered, as in the case of ethyl chloride, by limiting the amount of air during inhalation. The induction is much slower than in the case of the last two drugs, and it is accompanied by a feeling of suffocation, owing to the pungent odour of the ether. On that See also:account the anaesthetic is best started with nitrous oxide or ethyl chloride. The recovery is always marked by some nausea and very frequently by vomiting. The mortality is small during the actual operation, but fatalities from See also:respiratory complications later on are not uncommon. (4) Chloroform, CHC13, a colourless liquid of a penetrating odour, boiling at 63° C. It is administered in such a way as to ensure the See also:free admixture of air. To secure this the face-piece must be loosely-fitting, and the strength of the vapour so gradually increased that the patient is never inconvenienced or impelled to hold the breath. The induction is slow, occupying two or more minutes, but it is not at all unpleasant; nausea and vomiting during recovery are rarer than in the case of ether, but if they do occur they last longer. The mortality on the table
is about T in 2500.
The question as to which is the better anaesthetic, ether or chloroform, for See also:long operations, is a See also:moot point. In the hands of an experienced anaesthetist there is probably nothing to choose as regards safety, and the anaesthetic advantages of the latter are incontestable. In the hands of the less-experienced anaesthetist, ether is the more suitable drug. At the extremes of See also:life, chloroform is well taken, as it is also by See also:women in labour, and it is indicated where there has been See also:recent inflammation of the air passages. In operations, too, about the mouth,chloroform must be the drug used, as a closely-fitting mask is obviously impossible.
The introduction by inhalation of any of the above drugs into the organism produces an anaesthesia, the degree of which at any moment varies directly as the amount or tension of the vapour in the blood, and therefore also as the tension of the vapour in the inspired air. The organism in this case may be compared to an electric See also:lamp, of which the voltage is, say Too, a current of any less voltage will only produce a red See also:heat, however many amperes are forced through; with the voltage at Too the filament will be See also: For practical purposes four degrees of anaesthesia are described, through which a patient passes from unconsciousness to (in the last resort) See also:death: (I) A state of disordered consciousness, with analgesia; the patient's ideas are confused, the See also:special senses are disturbed, and though the application of stimuli to the skin causes no See also:mental impression, yet in response to them there may be what look like purposeful movements. (2) In the second stage there is complete loss of consciousness, and though the reflexes persist, the movements in response to the stimuli are purposeless. The muscles generally See also:act strongly. (3) The stage of surgical anaesthesia; there is a general muscular relaxation, with the loss of many of the reflexes, i.e. an operation may be performed without evoking any See also:movement on the See also:part of the patient, while the vital reflexes and the vital centres in the medulla are still active, and the See also:heart muscle is not paralysed. (4) Finally, the stage of See also:paralysis of the medulla, when the respiratory and circulatory centres are paralysed, and the heart muscle itself is poisoned and death ensues. The aim of the anaesthetist is to keep the patient in the third degree of anaesthesia, thus avoiding the movements of the second and the dangers of the See also:fourth; he therefore keeps the patient under close observation, and by watching the respiration, See also:pulse and facial aspect, is able to See also:judge the condition of the respiration and circulation. He has a further See also:guide in the lid-reflex, i.e. the movement of the eyelid when the globe is touched; this and the See also:size of the See also:pupil tell him to what extent the central nervous system is depressed and complete the See also:information he requires. It will have been observed that the administration of the above drugs is by inhalation, and has to be continued throughout the operation, the See also:reason being that all the drugs are as rapidly excreted as they are absorbed, especially by the lungs, and therefore no other method would be of any avail. That there are drugs which are sufficiently slowly eliminated to allow of an operation being performed between the moment of induction and that of recovery, cannot be doubted, and their discovery and use can only be a See also:matter of time. Even at the present time there is one, See also:urethane, which, if injected with a hypodermic See also:needle, soon produces a profound general anaesthesia. It has only been used on the lower animals, as its depressing effect on the respiratory centre contra-indicates its use in human beings. Local Anaesthesia.—Much See also:attention has recently been devoted to the discovery of methods by which the insensibility may be confined to the area of operation and the loss of consciousness avoided. Such a See also:procedure has been common for many years for small operations, but it is only lately that it has been success-fully applied to the severer ones. It is very doubtful whether local anaesthesia will ever replace general in the latter class. Though the preliminary See also:starvation is avoided, and the patient has the See also:shock of operation alone to recover from, without the cardiac depression resulting from the anaesthetic during the operation, the patient, unless of a very apathetic temperament, is in that state of severe nervous See also:strain, when any unexpected movement or remark, or sight of a soiled See also:instrument, may produce an alarming or fatal See also:syncope. The earliest local anaesthetic was See also:cold, produced by a mixture of See also:ice and See also:salt. In place of this cumbersome method, the skin is now frozen by means of a See also:fine spray of ether or ethyl chloride directed upon it. The spraying is discontinued when the skin becomes white, and it is then allowed to regain its colour. The moment this occurs the incision is made and will be quite painless. The recovery, like that from any other See also:frost-bite, is very painful, and the time during which an operation can be done is very See also:short; consequently this method has been very largely superseded by the use of drugs. The drugs chiefly used are See also:cocaine and its derivatives. Cocaine has by far the highest anaesthetic properties; it is, however, in certain individuals a most powerful cardiac depressant and has caused numerous fatalities, and further, it cannot be sterilized by heat, as it undergoes decomposition. Eucaine has now largely taken its place, though its anaesthetic properties are less; it is, however, less toxic, and can be909 sterilized by heat. In See also:combination with these drugs there is usually given some of the See also:extract of the suprarenal body of the See also:sheep; this substance increases and prolongs the anaesthetic effect by constricting the blood-vessels, the result of which is to reduce the See also:haemorrhage, and also to prevent the too rapid absorption of the drug into the general system, confining it to the area of operation. The See also:chief methods of bringing about local anaesthesia are as follows: (r) See also:Painting or spraying a See also:solution of the drugs on to the area on which it is proposed to operate. (2) Injection by means of a needle of the solution into the skin and the deeper structures. (3) Spinal analgesia. The method of inducing analgesia by injecting solutions into the sheath surrounding the spinal cord was devised by Bier in 1898, and for the purpose he employed a solution of cocaine. It was found, however, that there was considerable danger with this drug, so the method was not adopted to any great extent, until Fourneau discovered stovaine in 1904. The principle involved in spinal anaesthesia is this: that a substance in solution is injected into the See also:sac containing the spinal cord in the lumbar region. The spinal cord as such ends. at the level of the first lumbar vertebra in a leash of nerves termed the cauda equina. When giving an injection there is little danger of injuring these nerves because in this situation there is a space filled with fluid between the See also:wall of the sac and the nerves. The substances injected, by virtue of their specific See also:action on nervous tissues, cause loss of painful sensations in the lower limbs and for a variable distance up the See also:trunk. It has been found that the specific gravity of the solution injected has some influence on the height to which the analgesia will extend up the trunk, and this distance can also be controlled by altering the position of the patient. The See also:canal in which the cord is situated is not a straight See also:tube, but is curved backwards in the sacral and upper dorsal regions, and forwards in the lower dorsal and lumbar regions. Therefore with the patient lying on his back, any solution injected that has a greater specific gravity than that of the cerebrospinal fluid which bathes the cord, tends to gravitate towards the sacral and upper dorsal regions; and, conversely, any solution of lower specific gravity than that of the cerebrospinal fluid tends to rise and produce analgesia at a still higher level. In this way the situation of the fluid producing analgesia can be controlled to some extent. It has been found that a very serious danger exists if the solution passes. up to the brain, or even if it passes higher than the See also:sixth cervical See also:nerve. It is important that the osmotic pressure of the solutions employed should be as nearly as possible that of the cerebrospinal fluid, that is to say, the nearer the solution is isotonic with the cerebrospinal fluid, the better will be the analgesia, and the less will be the harmful effects. At present it has not been found possible to See also:separate in any of the substances employed the radicle which produces motor effects from that which blocks the See also:advent of sensory stimuli. Although both effects last only a short time there seems to be a certain See also:risk due to the temporary muscular paralysis, and in a patient with a tendency to See also:bronchitis this is a matter of considerable moment. The fluid is injected in the following manner. A puncture is made with a special trocar and canula in the lumbar region between the second and third or third and fourth lumbar spines. The sheath of the sac having been entered, as is evidenced by the loss of resistance to the point of the trocar, and by the fact that cerebrospinal fluid escapes when the trocar is withdrawn, the dose of the fluid selected is injected through the canula, which is then withdrawn. An important point is that the operation must be absolutely aseptic; great care is taken to sterilize thoroughly the See also:instruments, site of operation and fluid used. The patient is placed in that position which will yield the best and safest analgesia for the operation; it is essential, however, that the patient's See also:head be raised well above the level of the spine. The injection is followed very quickly, generally within three to five minutes, by the See also:production of analgesia, which lasts for a period varying from half an hour to two See also:hours. Various substances have been used for the injection, of which the following are the chief —tropacocaine, stovaine, novocaine, cocaine, eucaine and alypin. All of these have been combined with adrenalin hydrochloride with a view to limiting their action in one degree or another; and also with other inert substances in such ,quantity as will produce isotonic solutions of relatively high specific gravity. The points in favour of this method of producing analgesia are as follows: (a) The patient is not rendered unconscious, and is often able to assist at his own operation, such as by coughing or moving his limbs in any way as may be desired. (b) There are no troublesome after-effects, such as nausea, vomiting and thirst. (c) The formation of haematoma is less frequent. (d) Surgical shock is considerably lessened, especially in such operations as amputations and severe abdominal emergencies. (e) The risk attending a general anaesthetic is avoided. The disadvantages at present attending the method are: (a) A severe form of headache may sometimes follow, but this has seemed to depend on the kind of fluid injected, and in the recent cases has not been so frequent as in the early ones. (b) The paralysis of muscles. In a very few cases this has been permanent. The temporary paralysis of the muscles of respiration is See also:apt to be a serious matter. (c) Occasionally incontinence of urine and faeces occurs; this, however, has not been permanent except in a few of the earlier cases. (d) The uncertainty of the method, so that the analgesia is not always as complete as is desirable. (e) The analgesia for safety must be limited to a See also:line below the level of the second See also:rib in front. (f) The use of the See also:Trendelenburg position is impossible, or indeed the use of any position which involves lowering the patient's head. It would appear that the method undoubtedly has its uses, and that it will take its place in surgery and find its proper level. A large amount of work is being done on the subject, with a view of determining the limitations and possibilities of the method, the best kind of substance to use and the proper dose to employ. Finally, a large number of operations have been performed under a local anaesthesia produced by See also:hypnotism (q.v.), but this is a method that can only be used on selected cases. (H. C. Additional information and CommentsThere are no comments yet for this article.
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