In intrameatal operations the head should be wrapped in a sterilized towel, and a square of sterilized lint, having an aperture in the centre so as to expose only the auricle and meatus, should be placed over the side of the head and face. In operations on the mastoid process, and in those involving a post-auricular incision, the head should also be shaved for at least two or three inches beyond the region of the ear.
Anæsthesia. Both local and general anæsthesia are used. Unless contra-indicated for some special reason, and unless the operation is a very trivial one, it is wiser to give a general anæsthetic. Of these, chloroform is the most suitable in adults and infants, and the A. C. E. mixture in children. Ether, although it may be safer, is frequently a source of annoyance to the operator, as it tends to increase the hæmorrhage.
In order to produce local anæsthesia two methods may be employed: (1) The instillation of fluids into the meatus; (2) subcutaneous injection of fluids beneath the lining membrane of the meatus and into the surrounding parts of the auricle.
The solution usually employed is a sterilized aqueous solution of cocaine hydrochloride in varying strengths up to 20%, to which may be added equal parts of 1 in 1,000 adrenalin chloride solution; the latter not only increases its analgesic properties, but also acts as a powerful hæmostatic.
Instillation. As the auditory canal and the tympanic membrane are lined with epithelium which is very resistant to the absorption of fluids, complete anæsthesia is almost impossible to obtain. This method, therefore, is practically limited to such trivial operations as the curetting away or snaring off of granulations or polypi from the external or middle ear. To render anæsthesia more complete, the affected part may be finally rubbed over with a crystal of solid cocaine hydrochloride just before the operation—is begun. On the other hand, if the raw surface is large—for example, the wound left after a recently performed complete mastoid operation—the cocaine employed should not be stronger than a 5% solution in order to minimize the risk of poisoning. Gray of Glasgow has suggested, as a more penetrating anodyne solution, a mixture consisting of a 10% solution of cocaine hydrochloride in equal parts of aniline oil and absolute alcohol, a solution which he especially advocates in order to produce anæsthesia of the tympanic membrane before doing paracentesis.
Subcutaneous injection. This is a modification of Schleich’s method, and was first introduced by Neumann of Vienna. It consists in injecting a very weak solution of cocaine and adrenalin chloride subcutaneously beneath the periosteum lining the auditory canal. By this method even the complete mastoid operation has been performed, and in certain clinics it is used continually in the minor operations of paracentesis of the tympanic membrane, division of intratympanic adhesions, extraction of polypi, and ossiculectomy. A solution of beta-eucaine or novocaine may be used in preference to cocaine, as being less dangerous. According to Neumann, three solutions are necessary: (a) a 1 in 2,000 solution of adrenalin chloride containing a 1% solution of beta-eucaine; (b) a 1 in 3,000 solution of adrenalin chloride containing a 1% solution of cocaine; (c) a 20% solution of cocaine.
Fig. 177. Neumann’s Syringe for Subcutaneous Injection.
The syringe for injecting the solution has a capacity of 1 cubic centimetre, and for convenience its needle is fixed at an obtuse angle to the body of the syringe (Fig. 177). The technique of the injection depends on whether the operation is to be limited to the auditory canal and tympanic cavity, or is to involve the mastoid process.
If the complete mastoid operation is going to be performed, the needle of the syringe, now filled with the eucaine solution, is thrust through the skin about the middle point of the mastoid process, and a few drops of the solution are injected. The needle is then forced upwards towards the temporal ridge, at the same time being thrust in deeply until it touches the bone, so that a syringeful of the solution is injected beneath the periosteum. The needle is then withdrawn and reinserted at the same point, but in a backward direction, the solution being injected along the posterior portion of the mastoid process; in a similar manner the solution is injected downwards towards the tip of the mastoid. The ear being now pulled well forward, the needle is made to pierce the fold between the auricle and the mastoid process, just above the posterior ligament, and is pushed inwards between the anterior border of the mastoid process and the cartilage of the meatus, and a further syringeful of the solution is injected. A large speculum is now inserted into the ear, so that by pressing it against the wall of the meatus the skin, at the termination of the cartilaginous portion, is made to project in folds. The needle of the syringe, filled with cocaine solution, is pushed into this fold, and a few drops of the solution injected. By degrees the needle is still further pushed inwards, keeping it in close contact with the bony wall so that the fluid is injected beneath the periosteum. If the injection has been successful, a white bulging of the superior wall of the auditory canal will be noticed. To render anæsthesia complete, further injections may be made into the inferior and anterior walls of the auditory canal. Finally, a pledget of cotton-wool soaked in a 20% solution of cocaine is pushed into the tympanic cavity.