The point of the instrument should now engage the Eustachian tube; if, however, inflation shows this not to be the case the probability is that the catheter has been pushed too far backwards and rests on its posterior lip. This can be remedied by drawing it a little further outwards.
The second method. The catheter, with its beak turned downwards, is passed gently and rapidly along the inferior meatus of the nasal cavity, and at the same time rotated slightly outwards against the inferior turbinal bone. Whilst the catheter is within the nose, this outward rotation is prevented by the narrowness of the inferior meatus, but as soon as the beak of the catheter has passed behind the level of the inferior turbinal into the free post-nasal space, it will revolve outwards and upwards and in so doing will enter the Eustachian tube, which lies just behind and above the posterior end of the inferior turbinal bone.
Provided there be no abnormal obstruction within the nose, this method is an exceedingly simple one. With the practised hand the manipulation can be carried out so smoothly and quickly that the catheter will be in position before the patient has had time to realize the fact.
Difficulties. 1. Irritability of the mucous membrane. The passing of the catheter through the nose may set up a violent spasm of sneezing or coughing. When the beak has entered the post-nasal space, the irritation may cause such intense contraction of the palatal muscles that the point of the catheter may become fixed and its movement rendered impossible. If this takes place, the catheter should be withdrawn and the part anæsthetized by means of cocaine and eucaine solution, which is best applied locally on a pledget of wool at the end of a probe.
2. Partial nasal obstruction. On inspecting the nose the obstruction is usually found to be due to a deviated septum or spur, or to adhesions situated at its anterior part. Sometimes a passage can be effected by simply diminishing the curve of the catheter. At other times the obstruction can be overcome by introducing the catheter with its stem held upwards and outwards, so that on entering the nose the beak dips in beneath the anterior end of the inferior turbinal. As the catheter is pushed gently inwards its outer extremity is brought round with a circular movement so that it gradually assumes the horizontal position. No force must be used. As the catheter is pushed farther in, it may rotate to a varying degree according to the formation of the nasal cavity. Sometimes, indeed, the catheter may make a complete rotation during its passage through the nose. At other times, after the obstruction is passed, the catheter is best pushed through the nose with the beak pointing directly upwards. The great point is gentleness; the catheter should be allowed to take whatever position suits it best, but after the beak has entered the post-nasal space the stem should lie horizontally along the floor of the nose and its beak should point downwards.
3. Complete nasal obstruction. If the obstruction be one-sided, then the catheter must be introduced into the nasal space through the opposite side.
This is performed in the ordinary manner, except that the catheter must be longer and possess a larger curvature. On reaching the post-nasal space, its beak is turned round so as to point towards the outer canthus of the eye on the affected side. It may be necessary to alter the curve more than once in order to get the point of the catheter to exactly engage into the orifice of the Eustachian tube.
If both sides be completely obstructed, the only method to adopt is catheterization from the mouth. The ordinary catheter is used. It is passed into the mouth, its beak being directed upwards, until it reaches the posterior wall of the pharynx. The catheter is then pushed directly upwards until its stem impinges against the soft palate. The beak is then turned outwards until it lies almost horizontally. In this position it should enter Rosenmüller’s fossa. The catheter is now withdrawn a little and should be felt to pass over a slight obstruction—the posterior lip of the Eustachian orifice. By gently pressing the beak slightly outwards, it should engage within the entrance of the Eustachian canal.
4. Obstruction within the post-nasal space. A common error in introducing the catheter is to push it too far backwards, so that on rotation of the beak outwards it passes behind the Eustachian tube and lies in Rosenmüller’s fossa. In this position the sounds referred to the examiner’s ear through the auscultation tube during the act of inflation differ from the normal sounds in that they are soft and distant. In a case of doubt inflation should again be practised with the catheter in varying positions. If the catheter be in the correct position, the patient should be able to talk without discomfort, and there should be no tendency to retching or coughing. If, however, the beak lies in Rosenmüller’s fossa, considerable irritation is caused, and on inflation the patient feels the air in the throat and not in the ear.
Catheterization may be rendered difficult by the presence of a large pad of adenoids or of a tumour; or inflation of air into the Eustachian tube may be quite impossible owing to the occlusion of its pharyngeal orifice, the result of scarring.