The anatomy of the neck must be understood clearly so that inadvertent injury to nearby cranial nerves can be avoided (figure 2). The vagus nerve lies within the carotid sheath generally in a posterolateral position; injury will result in vocal cord paralysis. The hypoglossal nerve passes superficial to the carotid arteries 1 to 2 cm cephalad to the carotid bifurcation; injury will result in deviation of the tongue and dysphagia. The ansa hypoglossi branches from the hypoglossal nerve as it crosses the internal carotid artery and passes inferiorly to innervate the strap muscles. This may be sacrificed without significant consequence to facilitate exposure of the more distal internal carotid artery, allowing the hypoglossal nerve to be gently retracted superiorly. The carotid body is in the crotch of the carotid bifurcation. Dissection in this area may result in hypotension and bradycardia, cardiovascular effects that can be blocked effectively by injecting the carotid body with 1% lidocaine. The facial nerve is at the most cephalad extent of the incision and should be well out of the field anteriorly (figure 2).
After the described exposure has been obtained, the facial vein is divided, exposing the carotid bifurcation (figure 3). The carotid sheath is entered and opened superiorly and inferiorly. A vessel loop is passed about the common carotid artery proximally. A vessel loop is passed around the external carotid artery to facilitate later placement of a vascular clamp. A vessel loop or a 00 silk ligature then is passed doubly around the superior thyroid artery as a Potts tie to provide vascular control. The internal carotid artery is then dissected circumferentially at a point 1 cm distal to palpable disease and encircled with a vessel loop. Great gentleness is required and care is taken during this dissection to prevent plaque embolization.
If selective shunting is to be used, appropriate monitoring equipment (a transducer, extension tubing, and a 22-gauge needle) must be readied and carefully flushed with saline to free it of bubbles or particulate debris. Clamps are placed across the external carotid artery and common carotid artery, after which the needle is placed within the carotid artery to measure the carotid stump pressure (figure 4). Stump pressures greater than 40 to 50 mm Hg document significant collateral blood flow and are associated with a lower incidence of cerebrovascular accident. Care must be taken in the presence of extensive or ulcerated plaques to avoid plaque embolization with this maneuver. Some rely upon continuous electroencephalographic monitoring to gauge the adequacy of collateral blood flow and the requirement for intraluminal shunting; others choose to shunt all patients routinely; and still others may choose not to shunt patients at all but attain acceptable results.
Heparin is now given intravenously by the anesthesiologist at the surgeon’s discretion. Bulldog clamps are placed across the internal carotid artery, external carotid artery, and common carotid artery in sequence. An incision then is made on the anterolateral surface of the common carotid artery just inferior to the bifurcation. Potts scissors then are used to elongate the incision proximally and distally across the area selected for endarterectomy (figure 5). Care must be taken to extend the arteriotomy distally to a point beyond the end of the atheromatous plaque so that the endarterectomy can be performed entirely under direct vision. The incision is carried through the thickened intima into the lumen. The line of cleavage is within the media, leaving the adventitia and media externa for closure as indicated by the arrows (figure 6).
If intraluminal shunting is elected with a Pruitt-Inahara shunt it needs to be flushed and prepped ahead of time. Heparinized saline is flushed through the irrigating port and hemostats are placed on the proximal and distal limbs of the shunt directly adjacent to the irrigating port. The distal end is inserted first and the balloon is gently inflated to seal off back bleeding around the shunt (figure 7). The distal hemostat is opened and the distal limb aspirated back through the irrigating limb to remove all air. The hemostat is reapplied. The proximal end of the shunt is then inserted into the common carotid artery and the balloon gently inflated to prevent any antegrade flow around the shunt (figures 8 and 9). Overinflation is to be avoided to prevent tearing of the intima or prolapsing of the balloon over the end of the shunt and occluding flow. The proximal hemostat is removed and the limb aspirated through the irrigating port to remove any air or debris. The aspirating process should be repeated one more time and the hemostats removed to establish flow through the shunt. The shunt is checked with the Doppler probe to check for flow and the endarterectomy is then commenced. With experience and planning, placement of such a shunt should consume no more than 60 to 90 seconds.
Endarterectomy is begun in the distal common carotid artery, using a Freer elevator, blunt spatula, or a mosquito hemostat. The appropriate endarterectomy plane usually is identified easily in the mid to outer media, leaving a smooth, glistening reddish-brown arterial wall behind (figure 10).
This dissection is continued quite carefully in an attempt to elevate the plaque circumferentially. A blunt-tipped right-angle clamp is often valuable (figure 11). The plaque then is divided proximally with the Potts scissors to facilitate exposure. The endarterectomy proceeds distally in a meticulous fashion, care being taken to maintain a single endarterectomy plane. The most important aspect of the procedure is the delicate feathering of the endarterectomy at the distal boundary of the atheromatous plaque. No flap or shelf can be tolerated, since a technical fault will result in dissection after restoration of prograde flow with subsequent thrombosis and probable neurologic catastrophe. Plaque is removed similarly from the external carotid orifice by eversion endarterectomy allowing removal of the specimen (figure 12). All residual debris is removed carefully with forceps in a circumferential direction. A Kittner sponge also may be helpful in clearing the field of debris. Heparinized saline is used to irrigate the field, allowing free removal of clot. Forceful irrigation distally may reveal elevation of a distal flap that may require attention or tacking sutures (figure 13).