Veno-Venous Bypass

Veno-Venous Bypass

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A technique employed to mitigate the effects of obstructing the vena cava.

Anesthetic implications

History:

Occlusion of the inferior vena cava at the level of the diaphragm reduces venous return to the right atrium by up to 60%. Historically this technique provided an alternative route of venous return during liver transplant. Advances in surgical technique particularly, piggyback implantation with partial occlusion of the ICV, have reduced the dependence on VVB at many centers in the United States.

Technique:

The bypass circuit consists of a heparin bonded tubing, a centrifugal pump, and a heat exchanger. Inflow catheters are typically placed by the surgeons via cutdown. One canula is placed in the greater saphenous vein with its tip extending to the external iliac vein. A second inflow canula is placed into the portal system, either the portal vein or one of the mesenteric veins. Blood aspirated from these two canulas flows through the circuit to a centrifugal pump and through a heat exchanger finally re-entering the circulation above the caval obstruction via a canula placed into the subclavian vein or the internal jugular vein.

High flow, heparin bonding and the absence of an oxygenator obviate the need for systemic heparinization during VVB.

Initiation of bypass flow is sequential, initially inflow from the femoral is opened and bypass is initiated. Once stable flow is established the portal system drainage is added to the circuit. It is important to quantify the flow from the femoral system and the additional flow from the portal system. To adequately decompress the portal system an additional one liter per minute of additional flow should accompany the addition of portal inflow. Total flow is typically on the order of 2 to 4 liters per minute.

Alternatively percutaneous canulas may be placed by anesthesia, but this is not common.

Complications:

• Venous Air Embolism
• Circuit disconnect and hemorrhage
• Thrombosis

Monitoring:

Invasive arterial pressure monitoring is imperative to demonstrate adequacy of venous return and cardiac output.

Air embolism is not caused by circuit disconnection and sudden aspiration of large volumes of air, the centrifugal pump will seize and stop flow once air enters the pump head. Rather air embolism is caused by slow aspiration most commonly from cracks, or partially open fittings. A small steam of bubbles will pass through the pump and accumulate in the right heart and pulmonary artery. A small leak is typically not obvious to the naked eye, but may be detected by making a high point in the tubing after the heat exchanged where air can accumulate. A more sensitive means of detection is trans esophageal echo cardiography. Persistent presence of air in the right atrium should prompt immediate cessation of flow through the bypass circuit and examination for points of air entry.

Flow through the system should be monitored, when flow drops to low levels (threshold vary by institution but on the order of 400 cc per minute) the risk of thrombosis increases. Low flow should be brought to the attention of the surgeons, if flow can not be increased the bypass should be discontinued.

Related surgical procedures

Liver transplant, Liver resection, nephrectomy for RCC with extension into the IVC, other surgery requiring extended duration of caval obstruction

References

1. Gurusamy, Kurinchi Selvan; Koti, Rahul; Pamecha, Viniyendra; Davidson, Brian R (2011-03-16). Cochrane Hepato-Biliary Group (ed.). "Veno-venous bypass versus none for liver transplantation". Cochrane Database of Systematic Reviews. doi:10.1002/14651858.CD007712.pub2.
2. Sakai, Tetsuro; Gligor, Silviu; Diulus, John; McAffee, Richard; Wallis Marsh, J.; Planinsic, Raymond M. (2010-09). "Insertion and management of percutaneous veno-venous bypass cannula for liver transplantation: a reference for transplant anesthesiologists: Percutaneous veno-venous bypass in liver transplantation". Clinical Transplantation. 24 (5): 585–591.
3. Kim, H.Y.; Ko, J.S.; Joh, J.; Lee, S.; Kim, G.S. (2018-11). "Weaning of Veno-venous Bypass in Liver Transplantation: A Single Center Experience". Transplantation Proceedings. 50 (9): 2657–2660.