SVC syndromes related to unresectable bronchogenic tumors should not be considered for SVC revascularization and internal jugular to right atrium or extra-anatomical by-pass(es) are not earned. Indications for palliative SVC procedures are exc eptional and might be evoked for slow-growing diseases, e.g. mediastinal primary or secondary fibrosis or SVC thrombosis of unknown etiology. Postoperative graft thrombosis is at risk and can have serious consequences in terms of pulmonary embolism. In this sense, the status of the cephalic venous collateral pathway plays a major role. Since the proximal anastomosis needs to be performed either at the origin of the SVC or at the level of one or both brachiocephalic veins, SVC revascularization can be made only if there is an excellent patency at the level of the cephalic venous bed. Moreover, the proximal veins should have normal walls.

Obstructed SVC usually present a rich collateral venous circulation which can be competitive and re duce the flow through the graft. Indications in this situation should be individually evaluated to avoid graft thrombosis.

Primary angiosarcomas or leiomyosarcomas of the SVC are rare, usually asymptomatic and along with congenital aneurysms are other indications.

Further indications include iatrogenic, blunt or penetrating injuries. Iatrogenic SVC thrombosis that may require prosthetic replacement may be caused by prolonged Swan-Ganz, endocardial pacing and central venous catheters . Thoracic blunt trauma or disinsertion of the brachiocephalic veins during sternotomy are other rare causes, as well as Behçet disease.

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Transient cyanotic faces during SVC clamping are reversible after venous declamping. Facies petechiae may develop but are usually transient and disappear after 1 to 2 weeks after the operation.

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The effects of SVC clampage are different according to the degree of obstruction of the SVC. For patients whose SVC is completely obstructed or tightly stenosed, intraoperative venous clamping results in a negligible hemodynamical compromise since a functioning collateral venous network already exists and supplements the flow obstruction to the SVC. By contrast, when the intrathoracic or mediastinal disease does not obstruct the SVC, an even sharp venous clamping might induce an hemodynamicall y cascade of events including decreased cardiac inflow and outflow, increased venous pressure of the cephalic territory and alterations of the cerebral arterial-venous gradient leading to brain damage and intracranial bleeding.

For patients wi th SVC obstruction or tight SVC stenosis, venous clamping does not significantly modify cardiac output and cerebral circulation. Consequently, the duration of venous clamping is not a limiting factor and the operation can be carried out safely and routinely without taking into account the reconstructive SVC step. By contrast, for patients with nonobstructed SVC, venous clamping is associated with an hemodynamic compromise resulting in decreased cardiac output and increased venous pressure in the cephalic territory which may induce brain damage.

Several tools may mitigate this hemodynamic compromise in unobstructed SVC. i) Shunt procedures: intraluminal shunting of the blood from the brachiocephalic vein into the right atrium may re duce the hemodynamic consequences of venous clamping. However, whatever the type of shunt utilized, their major drawbacks are their potential thrombosis and that they fill the operative field making the performance of the distal anastomosis difficul t. ii) Pharmacological agents and fluid implementation: they should increase the venous blood return to the right atrium and maintain the physiological arterial-venous gradient in the cerebral territory. The first target is achieved by an adequate co mpensation of all blood losses by blood components and macromolecules. Since the cranial venous pressure may rise up to 40 mm Hg during venous clamping, maintenance of the cerebral arterial-venous gradient requires fluid administration (average 15- 20 mL/Kg) to normalize the cardiac output and eventually vasoconstrictive agents to increase the mean arterial pressure. iii) Shortening the venous clamping time. To reduce the venous clamping time (which can be prolonged up to 45 min), an accurat e surgical strategy should be defined. For right bronchogenic tumors with carinal or proximal pulmonary artery invasion, it is often easier to perform the vascular step first and then the airway procedure. During the latter, all attention should be d irected to avoid prosthesis bacterial contamination. For mediastinal tumors involving both upper lobes, operation should be made from the left to the right side. This permits a safe and immediate revascularization between the left brachiocephalic vei n and the right atrium; the right part of the excision is performed thereafter.

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Truncular replacement
It requires a tumor-free confluence of both brachiocephalic veins. This procedure, commonly associated to a right pneumonectomy, employs a straight not ringed PTFE graft (#18 or 20). After proximal (brachiocephalic veins confluence) and distal (cavoatrial junction) clampage, the invaded segment of the vein is completely excised. The proximal anastomosis between the SVC stump and the prosthesis is then performed first using a continuous 5-0 polypro pylene (Prolene, Ethicon, Inc., Somerville, NJ) suture started at the posterior aspect of the prosthesis in an in- to out-side fashion. After its completion, the distal anastomosis is then performed in the same way. Before tightening the stretches of the distal suture, the proximal clamp is released, the prosthesis is flashed with saline heparinized solution and deairation made. The distal clamp is then released and the knots tied. To avoid prosthesis kinking, the length of the graft should be adapted so that the distal anastomosis rests under tension.

Revascularization from the left brachiocephalic vein
This procedure, always performed through a median sternotomy, requires a ringed PTFE graft (#12 or 1 3). The ringed graft is imperative since after closure of the median sternotomy, the prosthesis may be too long, inducing thus its kinking. Minimal dissection of the left brachiocephalic vein is also mandatory to avoid its rotation above the proximal anastomosis. The distal anastomosis can be performed either on the right atrium or appendage or the inferior stump of the SVC.

Revascularization from the right brachiocephalic vein
Ringed grafts are preferr ed (# 12 or 14) to maintain their patency and to avoid their compression by the post-operative fibrosclerosis. The risks of kinking are minimal since the direction of the graft is almost vertical. The proximal anastomosis is not always easy to perform since the right brachiocephalic vein after its resection is often short; it has to be performed firstly. The distal anastomosis should be made on the SVC stump; this architecture results in the straightest and shortest graft. It is the revascularization of choice after resection of mediastinal tumors involving the origin of the SVC.

Revascularization of both brachiocephalic veins
Indications for revascularization of both brachiocephalic veins are extremely rare and confined only to those patients whose right or left-sided internal jugular vein is absent because of previous neck surgery (e.g. thyroid cancer surgery). In these rare situations, revascularization of a single brachiocephalic vein may result in an insufficient brain venous drainage. On the contrast, by revascularizing both brachiocephalic veins, the established venous circulation and hemodynamics is conserved. An Y-type graft should be avoided since it may result in thrombosis of the accessory limb of the Y-graft because the graft-to-graft anastomosis is thrombogenic (raw anastomotic surfaces); thus a separate distal implantation is preferable. The right graft should be anastomosed distally on the SVC stump (when possible) and the left one on the right atrium.

Apart from this indication, revascularization of both brachiocephalic veins decreases the blood flow through each graft and requires a more demanding technical procedure. For these reasons, SVC revascularization of the viable brachiocephalic vein with ligation of the contralateral brachiocephalic vein is preferred in almost all cases.

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