Some degree of asphyxia is a common complication of inhalational anæsthesia: indeed some small degree of it is almost unavoidable. It is hardly too much to say that the difference between a good and a bad anæsthetist is that the one recognises and deals with asphyxia in its early stages, while the other allows it to assume serious proportions before he becomes aware of its existence. The man who only realises that asphyxia is present when the patient is deeply cyanosed and has ceased to be able to draw any air at all into his chest may know much of the physiology of anæsthetic drugs, and be well up in complicated anæsthetic apparatus, but knows nothing of the proper practice of anæsthesia.
Asphyxia arises during anæsthesia from several causes. In the first place, the drug which the patient is inhaling and absorbing into the blood, turns out from his red corpuscles a corresponding quantity of oxygen. While this is only seen in its extreme form in the case of nitrous oxide gas, it is a factor acting even in the case of other anæsthetics. Secondly, during deep anæsthesia, the respiratory centre may be somewhat depressed, and the force and frequency of the respiratory act diminished. Thirdly, the respiratory passages may be partially or wholly occluded from mechanical causes. This is far the most important type of asphyxia, being the most common, the most fatal, and the most easily prevented.
(1) Clenching of the Jaws arises not uncommonly during anæsthesia, being specially frequent towards the end of the induction period. Since a very large proportion of individuals have nasal passages insufficient in bore to carry the full volume of respired air, respiration must be obstructed if the jaws are clenched.
(2) Falling Back of the Lower Jaw and Base of the Tongue over the Epiglottis.—This is always liable to happen after the muscles are deeply relaxed.
(3) Mucous or Blood or a Foreign Body is Drawn by Inspiration into the Air Passages.—Changes of position of the head may release mucous which has been gathering in some parts of the mouth or pharynx. For instance, if the head has been lying on the side for some time, a pool of mucous or saliva commonly gathers in the most dependent cheek, and unless this is mopped out before the head is brought into the mesial position, this pool will be suddenly tipped backwards, and very probably drawn into the larynx. Again, in operations upon the nasal or oral cavities, blood is always liable to be inspired, and not a few teeth have found their way into the air passages in the practices of dental surgeons who do not take precautions against this accident.
(4) Spasm of the Adductors of the Vocal Cords is one of the most common and most baffling incidents in anæsthesia. It announces its presence by the commencement of laryngeal stridor, a high-pitched crowing noise, which is as annoying for the surgeon and anæsthetist to hear as it is detrimental to the progress of a smooth anæsthesia. Inspired mucous or blood almost invariably sets it up, and the two conditions of fluid in the larynx and narrowing of the glottis from approximation of the cords, add their effects together, with resulting obstruction of a high degree.
Laryngeal stridor, however, frequently occurs even when no fluid has been inspirated. It may be set up as a reflex from the area of operation. Dilatation of the sphincter ani, and removal of the prepuce in circumcision, are two common examples of this. It is also undoubtedly sometimes caused by giving too strong a vapour during the latter part of the induction stage. Stridor unfortunately sometimes occurs from no obvious cause at all, or to speak more correctly, from causes which are at present not known to us. It is the author’s belief that one of these causes may prove to be morphia given as a preliminary to inhalational anæsthesia. In his experience, stridor has been more frequent with morphia than without, particularly if chloroform be the anæsthetic chosen. Beyond that he cannot at present go.
(5) Pressure upon the Air Passages of Neoplastic or Inflammatory Swellings in the Neck.—In such cases any obstruction which may exist before induction will probably become intensified during the process, and a complete arrest of respiration is not uncommon. Large goîtres are the most common type of neoplasm to give trouble, and all acute inflammatory conditions in the neck which extend towards the trachea are notorious for their tendency to give cause for anxiety during anæsthesia.
An animal, subjected to asphyxia, either mechanically or otherwise, shows the following signs:—
(a) Increase of the force and frequency of the respiratory movements of chest and abdomen. Even though there be a complete mechanical obstruction, increased efforts to breathe will still be made for some moments, although air no longer passes in and out of the chest.
(b) There is a considerable rise of blood pressure owing to a high degree of vaso-construction.
(c) The pupils dilate.
(d) Generalised convulsions.
(e) The animal succumbs finally from cardiac failure. No heart muscle can continue to function properly if supplied by the coronary arteries with venous blood. Moreover, the heart pump has to act against the greatly increased peripheral resistance induced by vaso-constriction. It must therefore be a matter of time only when the strongest and healthiest heart will cease to contract under the abnormal conditions of asphyxia.
There are in asphyxia, two alterations in the blood-gasses, i.e. lack of oxygen and increase of CO2. The action of these two conditions have been differentiated by experimental work (Starling, Kayala, Jerusalem), and one can say definitely that the excess of CO2 is the cause of the increased activity of the respiratory efforts, and that the remaining phenomena are due to oxygen starvation. This point is of some importance in considering anæsthetic methods in which re-breathing (breathing in and out of a bag) is practised. The use of such methods has often been thoughtlessly condemned as “poisoning the patient with his own CO2.” Within the limits usually practised, a re-breathing method does not involve any such risk, provided oxygen starvation does not occur. This point is referred to again in Chapter iv.
The classical signs of asphyxia above described are hardly to be expected in the operating theatre, but essentially the condition of the patient who develops respiratory obstruction while under an anæsthetic is similar to that produced experimentally in animals in the laboratory. The changes most easily observed are as follows:—
(1) Alteration of the colour.—Cyanosis shows itself earliest in the lips, and the lobules of the ears,—later the whole face becomes dusky.
(2) Dilatation of the pupil, which ceases to respond to the stimulus of light.
(3) The respiratory movements increase in depth and frequency.—The chest and abdominal walls heave forcibly; but
(4) The volume of air passing in and out of the glottis is diminished.—In complete obstruction, of course, none passes at all. In passing we may draw the moral that persistence of chest movements is no proof of the passage of air in and out of the chest: that can only be proved by hearing the movement of air through glottis and mouth or nose, or feeling it on the delicate skin of the back of the observer’s hand.
(5) True convulsions are not seen, unless we may consider the jactitation of deep N2O anæsthesia as such (see Chapter VII.). Nevertheless, there are obvious and most valuable signs of asphyxia to be found in the muscular system often quite early. These consist in the incidence of muscular rigidity, which is frequently observed first in the muscles of the abdominal wall. A surgeon performing laparatomy will notice at once the occurrence of this phenomenon, than which hardly anything can complicate and delay his task more effectively. The anæsthetist who knows his work will, upon hearing from the surgeon a complaint as to the rigidity of the abdominal wall, devote his attention first to securing a perfectly free air-way before deciding that a deeper anæsthesia is required.
Fig. 5.—Vicious circle of asphyxia.
Once asphyxia, especially mechanical asphyxia, has begun, it almost invariably tends to get worse. The engorgement affects among other venules, those which run under the mucous membrane of the respiratory tract, still further obstructing the passage of air. The muscular rigidity, moreover, soon manifests itself in the adductors of the vocal cords and the muscles which close the jaws: the patient has thus entered into a “vicious circle,” Fig. 5. It is evident that the prevention of the earliest signs of asphyxia is to the anæsthetist a matter of vital interest. The cardinal points to watch are as follows:—
(1) Keep the neck of the patient as far as possible in a natural position, i.e. do not either flex or extend the head unduly upon the body unless the nature of the operation demands such an unusual position.
(2) Maintain a free passage for air either through the nose or the mouth.
(3) Keep the lower jaw in good position throughout the administration.
(4) Avoid turning the face from the lateral to the dorsal (face up) position unless essential. If it has to be done, be careful first to mop out any “pool” from the dependent cheek.
(5) Deal as effectively as possible with the earliest appearance of laryngeal stridor.
Let us see how in a normal case, these rules can be applied. With the patient lying (or, in exceptional circumstances, sitting) in a comfortable position, the shoulders and head raised above the rest of the body and the face looking upwards (or straight forwards, in the case of the sitting patient), the anæsthetic is begun slowly, and the patient encouraged to take his time and to breathe naturally. At this stage the jaw needs no support, the muscles being neither relaxed by deep anæsthesia, nor spastic from asphyxia. With the advent of muscular relaxation, the head is turned to one side, that which is opposite to the side on which the surgeon will be working, being usually chosen. We must now determine whether the patient can breathe best through the mouth or the nose, and make sure that the channel chosen is as free as possible. In the majority of cases it will be found that respiration is oral, and that all that is necessary is to support the lower jaw by a finger hooked into the depression just below the symphysis mentes. The hands of the anæsthetist, therefore, take up a position from which in nine cases out of ten they will never require to be moved.
The hand of the side toward which the patient’s face is turned supports the jaw and keeps the face-piece or mask adapted to the face. The middle finger is pressed into the space below the symphysis mentis, and exercises traction forwards and a little upwards, thus preventing the jaw from slipping backwards; the index finger lies along the lower part of the mask, maintaining adaptation between it and the chin; the thumb bears on the mask higher up, keeping its upper part pressed against the bridge of the patient’s nose, and also serving as a point d’appui, or fulcrum, from which the jaw traction by the middle finger can conveniently be exercised. This grip once learnt is not fatiguing to the hand, and is in the author’s opinion one of the essential points for the beginner to master (see Fig. 28C, page 85).
The opposite hand holds the drop bottle, if the method in use is an open one, the wrist resting upon the uppermost side of the patient’s head.
Fig. 6.—Hewitt’s dental props.
Fig. 28C shows this grip in operation, while Fig. 28D shows the alternative frequently adopted. This alternative has various disadvantages. It covers up a larger part of the patient’s face than the method recommended, and it tends to tilt the mask sideways. The little finger is supposed to be hooking forward the jaw by pressing behind its angle, but such a method is very fatiguing if in use for more than a few moments.
In a proportion of cases, it is found that a free air-way cannot be maintained by these simple measures. Upper or lower teeth (or both) may be missing and traction upon the lower jaw only closes the mouth the more firmly. In most of these cases, the difficulty can be met by the use of the dental prop. These are made in various sizes and shapes, of which the best known are Hewitt’s and Bellamy Gardner’s (see Figs. 6 and 7). The latter are made of aluminium and are of small size only. They are the most convenient for cases with teeth both in the upper and lower jaw, but who suffer from a receding lower jaw not easily kept forward unless the prop is used as a rocker, as it were, upon which it can be slid forward. Hewitt’s props are of plated metal, with lead on the cups, to avoid injury to the teeth. They are made in five sizes, of which the middle and larger are very convenient for cases in which one or both rows of teeth are missing.
Fig. 7.—Bellamy Gardner’s Dental Props.
Fig. 8.—Phillips’ modification of Hewitt’s artificial airway.
For cases entirely without teeth, and in which a large flabby tongue is prone to fall back over the epiglottis, the mouth tube (Fig. 8) is very convenient. The rubber shank lies along the top of the tongue, the metal end lies between the gums. As originally introduced by Hewitt, the air-way was circular in cross section, but the flattened model figured is a distinct improvement. It was introduced by Dr Phillips.
Fig. 9.—Silk’s nasal tubes.
Occasionally one decides to facilitate nasal rather than oral breathing, and if the natural passages are inadequate, recourse may be had to the passage of a short piece of drainage tube of the calibre of a number 10 catheter, and about 3 inches in length. With such a tube in one or both sides of the nose, reaching from anterior to posterior nares, nasal respiration is usually possible even in much obstructed noses (Silk). (Fig. 9.)
Fig. 10A.—Bellamy Gardner’s tongue-clip.
Fig. 10B. Ring tongue forceps.
Fig. 10C. Glossotilt.
Fig. 11A.—Boxwood wedge for opening jaws.
Fig. 11B.—Wedge for opening jaws.
Fig. 11C.—Mouth gag.
If proper and timely use be made of one or other of these simple devices, the use of the tongue forceps is rarely necessary.
Occasionally, however, it may be required, and a suitable appliance should always be at hand for an emergency. Fig. 10 shows two types. The little clip of Mr Bellamy Gardner is preferable to the ring type, the passage of the spike through the tongue substance producing less after pain, than the bruising following the use of the other instrument. The third drawing in Fig. 10 is of an instrument not much known outside Edinburgh; it is called a glossotilt, and is intended to lever forward the base of the tongue, as an alternative to nipping the tip of the organ with forceps, and has, in the opinion of some, various advantages.
Before using either mouth prop or tongue forceps, it is occasionally necessary to use some mechanical means to lever open a tightly clenched jaw. The earlier one interferes in a case of mechanical asphyxia, the less necessity will exist for the use of such means. Fig. 11 shows two well-known mouth gags, and also a box-wood wedge, the use of which is less liable to injure teeth than a metal instrument. If a gag is used, the blades when closed should lie the one behind the other, not side by side. This ensures a minimal thickness to be inserted between the tightly clenched teeth.
This is of necessity difficult since the causation of the condition is in many cases obscure. The error common to most beginners, and to many who would resent such a title being applied to them, is to regard the appearance of stridor as an indication to deepen the anæsthesia. Whether the cause lie in local irritation of the laryngeal mucous membrane or in some stimulus from the area of operation, the condition is presumably always essentially a reflex spasm of the adductors of the vocal cords, but it is a reflex which may persist even in an anæsthesia so deep that the vital medullary centres are in peril.
The preventive treatment consists chiefly in following the other rules set forth above for the prevention of asphyxia with such faithful care, that the patient never enters into the vicious circle of asphyxia of which stridor is so prominent a feature. Patience in the induction stage—the avoidance of forcing the anæsthetic upon the patient—is a safeguard not to be forgotten.
Once the condition has arisen, it saves time to withdraw the anæsthetic altogether, and to allow the patient to breathe nothing but fresh air. Brisk friction of the lips with a rough towel often does good, presumably by setting up a “cross reflex.” In severe cases, a most valuable measure is the inhalation of pure oxygen, a cylinder of which should always be at hand in the operating theatre. Even an obstructed air-way will convey enough undiluted oxygen to reduce the venosity of the blood, and so cut across the “vicious circle.”
So much for the treatment of the early stages of asphyxia, the more advanced stages constitute one of the “accidents of anæsthesia,” and are dealt with in Chapter xvi.