The subclavian artery is so deeply placed, its connexions with important parts are so intimate and varied, and the branches are so large in proportion to the length of the trunk, that operations on this vessel present, in most cases, considerable difficulties to the surgeon. But the difficulties, it will be found, vary in different cases.
The last division of the artery, that beyond the anterior scalenus muscle, is the part which is most favourably circumstanced for the application of a ligature in the cases in which such an operation is most frequently called for, namely, aneurism affecting the artery in the axilla. This part is preferable chiefly because the vessel is here nearest to the surface and most remote from the origin of the large branches. But though the subclavian artery appears to be easy of access above the clavicle, while the parts are in their natural position, it is to be remembered that when an aneurism exists in the axilla, the clavicle may be so much elevated in consecpience of the presence of the tumour, as to be placed in front of the vessel, or even above it. In such circumstances, the artery lies at a great depth, at the same time that the structures in front and behind it (the clavicle on the one hand, the vertebrae with the muscles covering them on the other hand), cannot, in any degree, be drawn asunder to facilitate the steps of the operation. It is when the outer part of the clavicle is thus raised from the ordinary horizontal position, that the height to which the artery arches above the bone becomes a point of importance. In most cases it happens that a portion of the artery is a short distance (about an inch) above the clavicle but occasionally, as before mentioned it rises much higher; or it may be lower than usual, lying close behind the bone. If. in a case rendering the operation necessary, the clavicle should be unusually raised, the accessibility of the vessel in the neck will differ in these several conditions. In one, the artery could be arrived at only by proceeding from above downwards behind the bone ; in another, a part of it would still be higher than the bone. This will serve, in part at least, to account for differences in the time which the operation for tying the subclavian artery has occupied in the hands of different surgeons, and even in the hands of the same surgeon in different cases
The principal facts bearing on the actual performance of an operation on the third part of the subclavian artery, will now be briefly recalled. The most prominent or convex part of the clavicle, the part of the bone opposite which the vessel lies, will serve as a guide for the middle of the first incision, which is to be made a little above the clavicle, and parallel with it. If, (after noting with the eye, or marking on the surface the line at which it is desired to make the incision,) the integument be drawn downwards over the clavicle, the parts covering the bone may be divided with freedom.
With the integument, the platysma and several nerves are divided in this incision, but no vessel is endangered, except in those rare cases in which the cephalic vein or the external jugular crosses over the clavicle. It will, in most cases, be an advantage to add a short vertical incision, directed downwards to the middle of the horizontal one. Should the sterno-mastoid muscle be broad at its lower end, or should the interval between that muscle and the trapezius be insufficient for the further steps of the operation, a portion of the former muscle, or even of both muscles, must be divided.
The external jugular vein next presents itself with the veins joining it from the shoulder, and, as this vein is usually over the artery, it must be held aside, or it may be necessary to divide it. If divided, the lower end of the vessel requires the application of a ligature as well as the upper one, in consequence of the reflux of blood from the subclavian vein. The omo-hyoid muscle will be turned aside if necessary ; and now must be determined the exact position at which the artery is to be sought by division of the deeper fascia?. If the clavicle has its usual horizontal direction, the slight prominence on the first rib is the best guide to the vessel, where it rests on the rib. The brachial nerves are here, it is to be remembered, close to the vessel, — so much so, that the ligature has in several cases been passed in the first instance round one of them instead of the artery. But if, in consequence of the disease rendering the operation necessary, the outer end of the clavicle is much raised, then it will, in many cases, be more easy to place the ligature on the artery above the insertion of the scalenus muscle, or even behind that muscle. Above the tubercle on the first rib, the situation of the vessel may be ascertained by means of the brachial nerves and the scalenus muscle ; and, before the membrane covering them is divided, the position of these structures may be ascertained by the difference they offer to the touch. The cord-like nerves and the smooth flat muscle may thus be readily distinguished. At the same time the influence of pressure at a particular point, in controlling the pulsation in the aneurism, will, in this, as in other operations on the arteries, assist the surgeon.
Two or three weeks afterwards, the same surgeon being engaged in performing an operation of the same kind, was compelled to discontinue it for a time in consequence of the sufferings of the patient, and an hour and forty-eight minutes elapsed before the operation was concluded. The patient died of hemorrhage in four days ; and, on examination after death, it was found that the artery had been perforated with the aneurism needle. One of the large nerves, and half the artery, had been included in the ligature. This case is reported by Dr. Rutherford, R.N., who was present at the oporation, in "Edinburgh Med. and Surg. Journal," vol. XVI. 1820.
Before concluding the remarks on the third division of the artery, it should be mentioned that the suprascapular or transverse cervical artery may be met with in the operation, which in other cases may be complicated by the occurrence of a branch, or, however rarely, of branches taking rise beyond the scalenus muscle.
The second division of the subclavian artery is the part which rises highest in the neck, and on this account it may be advantageously selected for the application of a ligature when the vessel is difficult of access beyond the muscle. The chief objection to operating on the artery in this situation arises from the contiguity of the large branches. Care is necessary in dividing the scalenus muscle to avoid the phrenic nerve and the internal jugular vein. Moreover, the fact of the entire of the subclavian artery being in apposition with the pleura, except where it rests on the rib, must be borne in mind.
Some difficulty may arise from a change in the position of the artery, as when it lies between the fibres of the anterior scalenus, or when it is in front of that muscle ; but such cases are of very rare occurrence, and the knowledge of the fact that the vessel may be thus displaced will assist the surgeon in the event of difficulty arising from this cause.
Before it reaches the scaleni muscles the left subclavian artery may be said to be inaccessible for the application of a ligature, in consequence of its depth and its ' close connection with the lung and other structures calculated to create difficulty in an operation, among which may be mentioned the internal jugular and left innominate veins. To the difficulties resulting from the manner of its connection with the parts now named, must be added the danger of performing an operation in the neighborhood of the large branches.
On the right side, though deeply placed and closely connected with important parts, the first division of the subclavian artery may be tied without extreme difficulty. But inasmuch as the length of the vessel, between its three large branches on the one hand and the common carotid on the other, ordinarily measures no more than an inch, and often less, there is little likelihood of the operation in question being successfully performed in any case ; and the probability of success must be held to be still further diminished when it is considered that the length of the free part of the artery is sometimes lessened by one of the large branches arising nearer than usual to its commencement.
In order to place a ligature on the portion of the right subclavian artery here referred to, it is necessary to divide by horizonal incisions the three muscles which cover it, together with the layers of fascia between and beneath them. While the muscles are being divided, a branch of the suprascapular artery will probably require to be secured. The position of the inner end of the clavicle and of the trachea, and the effect of pressure with the finger on the circulation in the aneurism or in the limb, will assist the surgeon in finding the artery without dissecting the surrounding parts to an unnecessary and injurious extent — a precaution of importance in all cases. In the further steps of the operation, the exact position of the internal jugular vein, the vagus nerve, and the pleura, are to be well remembered.
The right subclavian artery is occasionally somewhat more deeply placed than usual in the first part of its course ; and this occurs when it springs from the left side of the arch, or, more frequently, when it separates from the innominate behind the carotid. The advantage of a knowledge of this fact I had an opportunity of putting to the test in an operation for aneurism at which I assisted a few years ago. The same arrangement of the vessels has since repeatedly come under my observation.
From Quain's Anatomy.