Surgery of carotid bifurcation.
The concept of diagnosis and management of carotid artery surgery has widely changed in the past two decades. A large proportion of such patients have extracranial and segmental block amenable to surgery. A successful revascularisation in such a lesion often relieves symptoms and prevents progress of the disease.
Special features of the circulation in the head and neck makes carotid arterial surgery a more complex undertaking than the limbs. There is a critical level of pressure and flow. Even short periods of failure to maintain them can result in a permanent neurological damage.
Blocks and aneurysm are the two common lesions affecting the carotid bifurcation. Both these lesions are responsible for symptoms by their virtue of obstruction and embolisation.
Fifteen patients underwent surgery for carotid bifurcation in the last 5 years in our unit at the K.E.M. Hospital, Bombay. Eleven out of fifteen patients had atherosclerotic occlusion while four had aneurysms of the carotid artery.
Four vessel angiography was routinely performed in all cases before surgery. Occlusion of the carotids usually restricts itself to an area around the bifurcation [Fig. 1]on page 216A. Apart from assessing the level of the block an aortogram also gives useful information regarding the state of other vessels supplying the brain.
Various surgical procedures were undertaken depending upon the type of lesion encountered.
Nine cases were operated under general anaesthesia while six were performed under local anaesthesia. In four cases a Javid's internal shunt was used to maintain circulation to the brain during surgery. Thrombo-endarterectomy (8 cases) was the procedure of choice for localised occlusion at the carotid bifurcation which forms the main; bulk of cases. When carotid artery was occluded from its origin to a considerable length, the occluded segment was bypassed with a graft (2 cases). A definitive treatment of excision with grafting (4 cases) was carried out for aneurysms in this region. One case had thromboendarterectomy with patch plasty. Our present choice is a PTFE graft which we feel forms an ideal substitute in this area.
Complications were very few; however, they were of considerable interest. Two cases had wound infection; one had permanent neurological deficit and one had injury to the hypoglossal nerve. It is important to note that there was no mortality in the present series.
All cases of carotid aneurysms were taken for early surgery. In cases of occlusive lesions with transient ischaemic attacks patients were subjected to four vessel angiography and surgery when indicated. An asymptomatic bruit over carotid was not even considered for investigations. Patients with acute stroke were essentially conserved and were subjected to aortography after their neurological status was stable.
Local anaesthesia was preferred in cooperative patients in whom a quick thrombo-endarterectomy was planned. In the remaining cases general anaesthesia with normal oxygen and carbon dioxide tension was used. In all cases, precautions were taken to avoid hypotension.
Carotid artery was exposed by a standard oblique incision medial to the stern mastoid and the face turned to the opposite side. Care was taken to avoid injury to the hypoglossal and vagus nerves. Excessive handling of the carotid artery was avoided. The patients were heparinised with 100 units per kg. of body weight.
In conscious patients when the carotid was clamped the time was noted. After each minute the patient was asked to move the opposite limbs. Most of those in whom paresis is likely to develop will show a weakness during the first 90 seconds. After 10 minutes it is assumed that temporary clamping is safe and endarterectomy is started.
The incision for endarterectomy lies over the common carotid artery and then carried over to the internal carotid artery [Fig. 2], on page 216A. Retrograde flow from the internal carotid was assessed. We prefer performing carotid artery surgery without an internal shunt. However, in four cases a shunt was felt necessary. In these cases, care was taken to expel all air before circulation to the internal carotid was established. The shunt was maintained by tightly snugging the loops over the common carotid and internal carotid arteries. Pulsations felt over the internal carotid artery guarantee an adequate circulation to the brain. In cases where replacement of a segment of carotid artery was necessary it was found convenient to pass the shunt through the lumen of the graft.
Polytetrafluoroethylene graft is our present choice for replacing a segment of the carotid artery [Fig. 3], on page 216A). It has also been used as a patch over the area of thrombo-endarterectomy. Six-0 polypropylene was used to suture and anastomose the carotid artery.
For removal of air from the carotid system the following sequence was used. The clamp over the internal carotid artery was removed first to wash out the debris and air. After this the internal carotid artery was re-clamped and the clamps over the common carotid and external carotids were released. Finally the clamp over the internal carotid artery was released.
Better understanding of the pathogenesis of stroke, improvements in the technology of carotid angiography and availability of improved vascular substitutes have made the surgery of carotid bifurcation relatively easy and safe. However, even today post-operative neurological deficit is the most feared complication of carotid surgery. Intra-operative efforts to minimise its occurrence has led to the development of a variety of techniques. Hypothermia enjoyed a period of popularity but has been discarded as its benefits were compromised by the threat of cardiac arrhythmias. Controversies still exist regarding the use of anesthesia and use of intraluminal shunts.
Javid et, al devised extremely smooth, highly flexible, polyethylene, tapered tubes. This group and others including DeBakey and Crawford, Tsapogas routinely use internal shunts. There is a tendency to hurry through the operation when a shunt is not inserted for the fear of neurological complications due to the prolonged anoxia. The rationale of using a shunt is to perform the operation in an unhurried meticulous manner.
For these cases a temporary shunt should always be set up. Whenever a shunt is preplanned or when the patient is not co-operative general anaesthesia is preferred. When local anesthesia is used, the patient is asked to obey simple commands such as move the fingers of the opposite side during cross-clamping. In the present series, patients with atherosclerotic blocks outnumbered those suffering from aneurysms. Aneurysms of the carotid artery is an uncommon but potentially serious problem [Fig. 4]& [Fig. 5], on page 2:16B. It carries the risk of expansion, rupture, haemorrhage and embolism. As against the Western literature5 where atherosclerotic and false aneurysms dominate the picture, in India syphilis remains the main etiological cause.
In only one case, neurological deficit in the form of monoparesis was observed. This incidence of 6.6% is well comparable to other series who have performed carotid surgery either with or without shunt. Wound infection is common, secondary to post-operative blood and fluid collection. This, however, can be minimised by a good haemostasis and by inserting a closed system vacuum drainage.
On the other hand, Baker et al, Wylie and Ehrenfeld, Heilbrun, and Young et al do not use the shunt routinely in carotid revascularisation. Wylie and Ehrenfeld suggest using an internal shunt only in patients with a carotid stump pressure below 40, mm.Hg., while Baker et all assure that in general, thromboendarterectomy can be performed safely without the use of shunts.
We have the distinct impression that the failure is due to the post-operative thrombosis rather than to the length of the occlusion. It is our belief that thoroughness of removing the plaque and smoothness of the remaining wall are of greater significance in the success than a few minutes of extra time taken. Our preference is to carry out revascularisation without a shunt wherever possible. The procedure is technically easier without, the impediment of a shunt. In addition, by its omission possible disruption of the intima of the internal carotid is avoided. In general, if there is poor back bleeding from the stump of the internal carotid artery, it is wise to use a shunt. Some cases are likely to require more detailed work taking longer to complete e.g. securing stitches to the distal edge of intima or placing a patch graft in an arteriotomy.