Intratracheal insufflation consists in driving a current of air under pressure, through a tube introduced by way of the mouth and larynx, deeply into the trachea. The current of air which is continuous, returns between the tube and the wall of the trachea, and escapes through the mouth and nose.
The work of Meltzer and Auer has demonstrated that this insufflation of air into the trachea under adequate pressure ventilates the pulmonary alveoli, and enables the normal diffusion of gases to be carried out for many hours, independently of all respiratory movements. If the air in its passage under pressure is made to pass through a chamber containing ether, we are enabled to introduce into the pulmonary alveoli, ether vapour of varying strength, and, by this means, to maintain surgical anæsthesia.
The Actual Process of External Respiration consists in the absorption of oxygen from the alveoli into the blood of the lung capillaries, and the elimination of carbon dioxide from the lung capillaries into the alveoli. The oxygen has to be brought from the outside to the alveoli, and the carbon dioxide has to be conducted from the alveoli to the outside. Between the outside and the alveoli is the long airshaft, consisting of mouth and nose, pharynx, larynx, trachea, bronchi and bronchioles. In natural respiration the conduction of oxygen inwards, and of carbon dioxide outwards, is carried through by a complicated pumping mechanism. In ordinary inhalation anæsthesia, this mechanism is entrusted with the task of introducing ether vapour into the alveoli.
In intratracheal insufflation the work of this natural pumping apparatus is taken over by an artificial mechanism. In considering the justification for this, the following points are to be noted:—
(1) The patient is unconscious—not naturally so as in sleep—but unnaturally as the result of drugs; there is therefore a probability that the elaborate natural mechanism may not work smoothly—especially is there a danger that the free airway may be interfered with. Intratracheal insufflation obviates this danger.
(2) By means of the artificial mechanism, air is brought with some force to the mouth of the bronchi, and thus a more rapid and more powerful diffusion of gases takes place.
(3) The mechanism ensures the maintenance of a current of air blowing forcefully from the trachea and larynx through the pharynx, mouth and nose. This re-current continuous air-stream effectively prevents the entrance of blood or any infectious material into the bronchi and air cells, and thus the danger of septic lung troubles is obviated.
(4) In certain intrathoracic operations the normal respiratory mechanism is deliberately interfered with. Intratracheal insufflation by the constant maintenance of sufficient positive pressure, prevents or regulates the collapse of the lung which occurs when the thorax is opened, and thus obviates the necessity for the somewhat elaborate positive and negative pressure cabinets and masks which had been devised for intrathoracic operations.
(5) Incidentally it may be noted that intratracheal insufflation of air provides us with an excellent means for performing artificial respiration. Many instances have now been recorded of its utility in this respect. Dr Elsberg records the case of a patient who had taken morphia with suicidal intent, on whom artificial respiration by this method was kept up for 12 hours, without any respiratory movements taking place, recovery ultimately ensuing.
This consists of (see Fig. 30):—
1. Instrument for producing air current (A).
2. Ether chamber and various regulating taps (B).
3. Device for warming vapour (C).
4. Safety valve (D).
5. Manometer (E).
6. Intratracheal catheter, with rubber tubing linking up the various parts of the apparatus (H).
Fig. 30. Diagram of intratracheal apparatus.
1. The Air Current is obtained either by means of an ordinary glass-blower’s foot bellows, or an electric motor may actuate a rotatory blower which produces a current of air. The blower may be made to rotate at a speed varying from 50 to 1000 revolutions per minute (see Fig. 31).
The foot bellows is simple and inexpensive, and there is no reason why it should not be efficient. The electrically rotated blower is more efficient, ensures a smoother air current, and saves much labour.
2. The Ether Chamber.—Ether vapour may be produced by either of two methods. Fig. 32 shows Kelly’s instrument where air is blown over the surface of a considerable quantity of liquid ether. Dr Meltzer[5] maintains that the effectiveness of the etherization is proportional to the diameter of the ether bottle. In this connection it may be well to recall certain points pertinent to the subject of etherization. A satisfactory etherization depends on the establishment in the blood and tissues of an ether tension of definite strength. Boothby[6] states that this tension should correspond to about 15 per cent. of ether vapour in the alveolar cells. “If when this tension has been established, less than 15 per cent. ether vapour is administered, outward diffusion occurs from the tissues and blood to the air and the anæsthesia becomes lighter.”
Fig. 31.—Electric blower to supply current of air for intratracheal anæsthesia.
Fig. 32. Kelly’s intratracheal apparatus.
In an apparatus such as we are describing the strength of the ether vapour depends on and is influenced by a variety of factors, among which the following may be specially noted:—
(a) The diameter of the ether chamber.—The larger the diameter the stronger will be the ether vapour. The chamber is generally kept two-thirds full: the less the empty space in the chamber the stronger will be the vapour.
(b) The rapidity of the air-current.—The larger the amount of air passing over the ether the more rapid will be the vapouration, with the result that the temperature of the liquid ether will rapidly fall and the strength of the ether vapour in the air will be correspondingly lowered.
(c) The temperature of the liquid ether.—The higher the temperature of the liquid ether the stronger will be the percentage of ether vapour in the air. If the ether chamber is placed in a bath of water which is maintained steadily at an adequate temperature and if the rate of the air flow remains constant, a constant strength of ether vapour will be given off. It is well in this connection to remember that the boiling point of ether is low and that a very high percentage of ether vapour is readily obtained if the temperature in the water bath is allowed to rise beyond 80°F. For further information regarding ether percentages see Appendix I and II.
Such an instrument as Kelly’s requires at its head a regulating tap, movement of which is capable of diverting part of the air stream direct to the patient without coming in contact with the surface of the ether. In this way the maximum strength of vapour may be diluted as and when required.
In Fig. 33 is shown Shipway’s instrument. Here the drug is dripped into a chamber, the floor of which is kept warm. The ether volatilises at once and the vapour is carried away by the air stream passing through the chamber. The strength of ether vapour in this instrument is regulated solely by the rate of drip which is in complete control of the administrator.
Whichever method of making ether vapour is utilised the instrument should be capable of producing a maximum at least of 15 per cent. to 18 per cent., and means must be provided to reduce this percentage at will.
3. Device for Warming Vapour.—It is doubtful if the warming of inspired or insufflated vapour has any appreciable influence on the body temperature, but there is a fairly general consensus of opinion that if the ether vapour is warmed there is less likelihood of irritation of the respiratory mucous membrane. It is to be noted, moreover, that in intratracheal insufflation the natural apparatus for warming the inspired air is put out of action. This warming can be effected by the simple device of carrying the tube through a chamber of hot water after it emerges from the ether chamber.
4. Safety Valve.—Dr Meltzer insists very strongly on the necessity of having a safety valve capable of controlling the maximum pressure under which the air may enter into the intratracheal tube. By a simple device, any excess of desired pressure will cause the air to bubble through mercury and thus never reach the lungs. In this way any possibility of accident from undue intrapulmonary pressure is obviated.
Fig. 33.—Shipway’s intratracheal apparatus.
5. Mercury Manometer to indicate the pressure in the tube in m.m. of mercury. It has been experimentally established[7] “that the pressure in the trachea and in the bronchi is only a small fraction of the pressure in the manometer outside of the body, and that the intratracheal pressure grows considerably less with the decrease of the diameter of the intratracheal tube.”
6. Intratracheal Catheter.—It is essential to have an instrument of adequate rigidity which can be satisfactorily sterilized. The ordinary coudé catheters, or the silk web white enamelled cylindrical catheters, are suitable. The size should be selected from a range of 18 to 25 French. It is preferable to err rather on the side of a small than a large tube. An ordinary adult will require a tube of about size 22 to 24, a plethoric alcoholic, on the other hand, might need a 25.
A tube of too large a calibre interferes with the free return of air and spontaneous respiration soon becomes too slow. Expiration is prolonged, active, and laboured, and after a few minutes, respiratory movements may cease entirely. The only way to meet such a situation is to withdraw the tube and insert a smaller one.
Technique of Administration.—It is advisable in adults to administer about three quarters of an hour before the operation, a hypodermic injection of morphia (gr. ⅙) and atropine (gr. ¹⁄₁₀₀), or of scopolamine (gr. ¹⁄₁₀₀) and morphia (gr. ⅙). The latter combination is more efficacious in alcoholic subjects. In children, atropine alone should be given.
It is to be remembered that intratracheal insufflation of ether is a method of maintaining not of inducing anæsthesia. Induction is carried out in the ordinary way. When this has been done, the catheter is passed.
The introduction of the catheter does present some difficulty, but this is largely overcome as skill and confidence are acquired with practice. It may be carried out indirectly, or a view of the glottis may be obtained by the aid of such an endoscope as Hill’s, and the catheter inserted between the cords. The latter method is probably the more satisfactory, but it is well to acquire the skill to pass the catheter indirectly as in a certain small proportion of cases there are obstacles to the use of the endoscope.
To facilitate catherization the pharynx and epiglottic region may be cocainized with a 5 per cent. solution before induction. Hill’s endoscope (Fig. 34) is distally illuminated by a small electric lamp, which is connected with a small pocket battery. A useful modification of this has been devised by Mr Dott. In it, the catheter is passed along a separate compartment, so that the view of the glottis is undisturbed. The point of the catheter comes into view at the distal extremity of the endoscope and can be guided between the cords into the trachea.
Fig. 34.—Hill’s Direct Laryngoscope.
It is essential before attempting intubation, that there should be thorough relaxation. The lower jaw should be so slack that a gag is not required. The head is then placed in the occipito-shoulder position, or is allowed to hang over the end of the table. The tongue is controlled by forceps, and the endoscope passed slowly along its dorsum until the epiglottis comes into view. The point of the endoscope is then passed sufficiently far below the tip of the epiglottis to ensure that it will not slip; too deep insertion must be avoided. The endoscope being held in the left hand, the hyoid bone is lifted up by a tilting movement of the hand. The glottis is thus brought into view. The catheter stiffened by means of a probe is then passed through the glottis into the trachea and the endoscope withdrawn. The bifurcation of the trachea in the adult is at a distance of about 26 cm. from the incisor teeth. The catheter should be marked accordingly, and inserted to a point just short of this. The probe is then withdrawn, and connection made with the air current.
It occasionally happens that unexpected difficulty is met with on attempting to pass the catheter by direct vision. The larynx may be so fixed that the glottis does not readily come into view; or in the case of an intraoral neoplasm the view may be obstructed by the presence of blood. In such cases the catheter can be introduced by the indirect method. The middle finger of the left hand is passed along the dorsum of the tongue until the epiglottis is felt. The index finger is then used to guide the point of the catheter to the glottis through which it is then passed. No undue force must be used. A stilette should be inserted into the catheter which should be moulded almost to a right angle at its terminal third. If the stilette is withdrawn when the point of the catheter is over the mouth of the glottis, the instrument will, as a rule, slip easily into the trachea.
Occasionally the tube passes into the œsophagus. With care and adequate relaxation such a mistake should not occur, but the possibility of it should be kept in mind. If the operator will abstain from attempting to pass the catheter until such time as he has a satisfactory view of the glottis, mistakes of this kind will seldom occur. The essentials are a good illumination and an adequate relaxation.
Mild glottic spasm may supervene on the passage of the catheter but this rapidly passes off. At first the degree of concentration of the vapour should be low or irritation will result, evidenced by spasm and coughing. The strength of the vapour is gradually increased until the necessary concentration is attained. The pressure should vary according to the requirements of the case and should range between 10 mm. to 25 mm. Hg. The safety valve must be set so as to make any pressure above this impossible.
In the majority of cases the course of anæsthesia is smooth and uneventful; the colour remains a rosy pink, the pulse is good, and the respirations quiet and regular. It is undesirable that the respiratory movements should be abolished altogether; their presence indicates that neither the central nor the peripheral respiratory mechanism is being overdosed with ether.
Theoretically, the constant plus-pressure in the lungs might be thought to interfere with the circulation in the large veins, and in the pulmonary vessels themselves. It is therefore well to reduce the pressure in the catheter to zero every minute by opening the tap provided for the purpose for a second or two.
At the conclusion of the operation, before withdrawing the catheter it is well to flush out the lungs with air so as to remove any ether vapour that is present. In a certain number of cases, notably in big alcoholic subjects, difficulty may be experienced in securing a sufficiently deep anæsthesia with good relaxation. It is seldom, however, that patience and the careful introduction of a stronger vapour will not suffice to overcome this. In alcoholic subjects, as previously suggested, preliminary medication with scopolamine and morphia will help. It really becomes a question, if one may put it so, of coaxing the unconscious patient to tolerate an ether vapour of adequate strength.
The general opinion of anæsthetists appears strongly to favour the view that the absence of strain and the perfect æration in intratracheal ether insufflation tend to lessen the shock of operation. The post-operative history of patients also suggests that there is a lessened liability to pulmonary complications as compared with cases in which ether has been administered by other methods. Dr Elsberg[8] of New York in this connection writes: “The absence of any pulmonary complications has led us to use this method of anæsthesia in all patients in whom pulmonary complications were to be feared after an anæsthesia or operation. Thus on all asthmatics, in patients with chronic bronchitis and emphysema, in patients who require gastric resection and the like, we no longer, during two years, have seen the much dreaded post-operative pneumonia wherever intratracheal anæsthesia was used.”
In addition, there is ample evidence[9] that the introduction of a catheter into the trachea and its presence therein does not tend, as might have been expected, to set up any irritation at the time or predispose to subsequent trouble. Apart from these general considerations, which suggest the advantage of a somewhat extended use of intratracheal ether insufflation, the method has obvious advantages in all operations about the mouth, such as those for excision of the upper jaw, those undertaken for the removal of nasopharyngeal growths and various plastic operations involving the nasal and buccal cavities. In such cases the danger of aspiration of blood, mucus, etc., is obviated and the anæsthetist is well out of the surgeon’s way, while at the same time an even interrupted delivery of ether vapour is effected. In operations for removal of glands in the neck the surgeon has the field to himself, and is not hampered nor is his asepsis endangered by the proximity of the anæsthetist’s mask.
In such operations as laminectomy and nephrectomy the postural difficulties with which the anæsthetist has to contend, and which also tend to interfere with free respiration, are eliminated.
The great advantage of the method in intrathoracic operations has already been referred to.
The introduction of intratracheal insufflation of ether was rendered possible by the pioneer work of Drs Elsberg, Meltzer, and Auer. The writer would like to acknowledge his indebtedness to their writings, of which he has made free use.