Anaesthesia
ANAESTHESIA and ANAESTHETICS , terms used in medicine to describe a state of local or general insensibility to external impressions, and the substances used for inducing this state. In diseases of the brain or spinal cord anaesthesia is an occasional symptom, but in such cases it is usually limited in extent, involving a limb or a definite area of the body's surface. Complete anaesthesia occurs in a state of catalepsy or trance- conditions associated with no definite lesion of the nervous system.
The artificial induction of anaesthesia has come to occupy a foremost place in modern medicine, but there is abundant evidence to show that it is a practice of great antiquity. Besides the mention by Homer of the anaesthetic effects of nepenthe, and the reference by Herodotus to the practice of the Scythians of inhaling the vapours of a certain kind of hemp to produce intoxication, the employment of anaesthetics in surgery by the use of mandragora is particularly alluded to by Dioscorides and Pliny. It also appears, from an old Chinese manuscript laid before the French Academy by Stanislas Julien, that a physician named Hoa-tho, who lived in the 3rd 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 Hugo de Lucca, who practised in the 13th century. The soporific effects of mandrake are alluded to by Shakespeare, who also makes frequent mention of anaesthetizing draughts, the composition of which is not specified.
In the Medical Gazette, vol. xii. p. 515, Dr Sylvester, quoting from a German work by Meissner, published in 1782, mentions the case of Augustus, king of Poland, who underwent amputation while rendered insensible by a narcotic. But the practice of anaesthesia never became general, and surgeons appear to have usually regarded it with disfavour. When, towards the close of the 18th century, the discoveries of Priestley gave an impetus to chemical research, the properties of gases and vapours began to be more closely investigated, and the belief was then entertained that many of them would become of great medicinal value. In 1800, Sir Humphry Davy, experimenting on nitrous oxide (the so-called "laughing gas"), discovered its anaesthetic properties, and described the effects it had on himself when inhaled with the view of relieving local pain. He suggested its employment in surgery in the following words:-"As nitrous oxide, in its extensive operation, seems capable of destroying physical pain, it may probably be used with advantage in surgical operations in which no great effusion of blood takes place." His suggestion, however, remained unheeded for nearly half a century. The inhalation of sulphuric ether for the relief of asthma and other lung affections had been employed by Dr Pearson of Birmingham as early as 1785; and in 1805 Dr J. C. Warren of Boston, U.S.A., used this treatment in the later stages of pulmonary consumption.
In 1818 Faraday showed that the inhalation of the vapour of ether produced anaesthetic effects similar to those of nitrous oxide; and this property of ether was also shown by the American physicians, John D. Godman (1822), James Jackson (1833), Wood and Bache (1834).
These observations, however, appear to have been regarded in the light of mere scientific curiosities and subjects for lecture- room experiment, rather than as facts capable of being applied practically in the treatment of disease, till December 1844, when Dr Horace Wells, a dentist of Hartford, Connecticut, underwent in his own person the operation of tooth-extraction while rendered insensible by nitrous oxide. Satisfied, from further experience, that teeth could be extracted in this way without pain, Dr Wells proposed to establish the practice of painless dentistry under the influence of the gas; but in consequence of an unfortunate failure in an experiment at Boston he abandoned the project. On the 30th of September 1846 Dr W. T. G. 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 America in numerous instances under ether inhalation, the result being only to establish more firmly its value as a successful anaesthetic. The news of the discovery reached England on the 17th of December 1840. On the 19th of December Mr Robinson, a dentist in London, and on the 21st Robert Liston, the eminent surgeon, operated on patients anaesthetized by ether; and the practice soon became general both in Great Britain and on the continent.
Sir James 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 child. On the 8th of March 1847 M. J. P. Flourens read a paper before the Academie des Sciences on the effect of chloroform on the lower animals, but no notice was taken of what has since proved to be a discovery of epoch-making importance. In November of the same year Simpson announced his discovery of the anaesthetic properties of chloroform, the trial of which had been suggested to him by Waldie, a chemist of Liverpool. As the result, chloroform came to be widely used instead of ether, though it was found by several casualties that it was not the absolutely safe anaesthetic that had at first been hoped. It, however, remained the drug that was chiefly used till Dr J. T. Clover (1825-1882) of London introduced his regulating ether-inhaler in 1876, embodying a new principle-that of limiting the quantity of air during etherization and regulating the strength of the vapour.
During the intervening period, as the results of the labours of John Snow, Sir Benjamin Ward Richardson, Thomas Nunnely, and Colton amongst others, several drugs were found to possess anaesthetic properties. Of these one, ethyl chloride, which was speedily given up, has come into deserved prominence at the present time; and another, nitrous oxide, which had been lost sight of since Wells's failure at Boston, was reintroduced, and it became and has remained the most popular anaesthetic in dental practice.
Since 1876 no new drugs have been introduced; the progress has been in the direction of improvements in the technique of anaesthetization. The most important of these is the administration of oxygen with nitrous oxide, resulting from the recognition of the fact that this drug does not owe its anaesthetic properties to partial asphyxia, as was thought till the contrary was shown by Edmund Andrews of Chicago in 1868. It was not till twenty years later that this knowledge was put to practical use, when F. W. Hewett introduced his regulating stopcock, which enabled the anaesthetist to exhibit the nitrous oxide and oxygen in such proportions as were demanded by the patient's condition. At the present time the anaesthetics in common use are the following:-
(1) Nitrous oxide gas, or laughing gas, N2O. This is a colourless, odourless gas, which for convenience is carried about in liquid form in iron cylinders. When about to be used, it is allowed to escape into a large rubber bag, connected with a closely- fitting face-piece, which covers up the nose and mouth, and allows of 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 minor surgery where absolute muscular relaxation is not required. When mixed with oxygen, it can he given if necessary for an hour or longer. It has an induction period of a few breaths only, and the recovery is as a rule unaccompanied by excitement or nausea. It is also used as a preliminary to ether; the gas is given till unconsciousness is reached, the unpleasant 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 expert hands nil.
(2) Ethyl chloride, C2H5Cl, a colourless liquid of a pleasant odour, boiling at 12.5 deg. C. It is used in the same class of operations as the last anaesthetic. It is best given in an apparatus that consists of a mask closely adapted to the face, and a rubber bag of small capacity, with which is connected the 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 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)2O, a colourless, volatile liquid, boiling at 36.5 deg. 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 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 respiratory complications later on are not uncommon.
(4) Chloroform, CHCl3, a colourless liquid of a penetrating odour, boiling at 63 deg. C. It is administered in such a way as to ensure the 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 1 in 2500.
The question as to which is the better anaesthetic, ether or chloroform, for long operations, is a 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 life, chloroform is well taken, as it is also by women in labour, and it is indicated where there has been 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 lamp, of which the voltage is, say 100; a current of any less voltage will only produce a red heat, however many amperes are forced through; with the voltage at 100 the filament will be white hot, at over 100 the filament will fuse. So with these drugs: with the vapour at a low tension a certain low depth of anaesthesia is obtained; if the administrator increases the tension, true surgical anaesthesia is produced; if he increases it again, the filament fuses and the patient dies. This is the principle which guides the anaesthetist; it is the quality of the vapour that decides the depth of the anaesthesia, not the quantity. An infinite quantity of chloroform may be absorbed with impunity if the tension be low, but a few drops will kill if the tension be high. For practical purposes four degrees of anaesthesia are described, through which a patient passes from unconsciousness to (in the last resort) death:-
(1) A state of disordered consciousness, with analgesia; the patient's ideas are confused, the special senses are disturbed, and though the application of stimuli to the skin causes no 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 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 movement on the part of the patient, while the vital reflexes and the vital centres in the medulla are still active, and the heart muscle is not paralysed.
(4) Finally, the stage of 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 fourth; he therefore keeps the patient under close observation, and by watching the respiration, pulse and facial aspect, is able to judge the condition of the respiration and circulation. He has a further guide in the lid- reflex, i.e. the movement of the eyelid when the globe is touched; this and the size of the pupil tell him to what extent the central nervous system is depressed and complete the 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 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 matter of time. Even at the present time there is one, urethane, which, if injected with a hypodermic 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 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 procedure has been common for many years for small operations, but it is only lately that it has been successfully applied to the severer ones. It is very doubtful whether local anaesthesia will ever replace general in the latter class. Though the preliminary starvation is avoided, and the patient has the 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 strain, when any unexpected movement or remark, or sight of a soiled instrument, may produce an alarming or fatal syncope. The earliest local anaesthetic was cold, produced by a mixture of ice and salt. In place of this cumbersome method, the skin is now frozen by means of a 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 frost-bite, is very painful, and the time during which an operation can be done is very short; consequently this method has been very largely superseded by the use of drugs. The drugs chiefly used are 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 be sterilized by heat. In combination with these drugs there is usually given some of the extract of the suprarenal body of the sheep; this substance increases and prolongs the anaesthetic effect by constricting the blood-vessels, the result of which is to reduce the haemorrhage, and also to prevent the too rapid absorption of the drug into the general system, confining it to the area of operation.
The chief methods of bringing about local anaesthesia are as follows:-
(1) Painting or spraying a 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 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 wall of the sac and the nerves. The substances injected, by virtue of their specific action on nervous tissues, cause loss of painful sensations in the lower limbs and for a variable distance up the 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 canal in which the cord is situated is not a straight 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 sixth cervical 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 separate in any of the substances employed the radicle which produces motor effects from that which blocks the advent of sensory stimuli. Although both effects last only a short time there seems to be a certain risk due to the temporary muscular paralysis, and in a patient with a tendency to 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 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 head be raised well above the level of the spine. The injection is followed very quickly, generally within three to five minutes, by the production of analgesia, which lasts for a period varying from half an hour to two 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 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 line below the level of the second rib in front. (f) The use of the Trendelenburgh 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 hypnotism (q.v.), but this is a method that can only be used on selected cases. (H. C. C.)
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)
