Explain Bidirectional Glenn Shunt under cardiopulmonary Bypass ?

The ascending aorta and SVC at innominate jugular vein junction and IVC are cannulated and child connected to cardiopulmonary bypass. The operation is done at normothermia. Systemic pulmonary artery shunt is ligated off. Pulmonary trunk is clamped, divided and both end over sewn. The azygos vein is ligated so that there will be no run-off of superior vena caval blood away from pulmonary circulation. Vascular clamps are applied on the superior vena cava and it is divided at a point where it crosses right pulmonary arteiy.

End of the SVC near right atrium is over sewn. After applying a partial occlusion clamp on the right pulmonary artery, its upper border is incised and end of superior vena cava anastomosed. This establishes unhindered flow of SVC blood into both pulmonary arteries (BDG).