One of the major surgical complications after pancreas transplant is early graft failure due to thrombosis. Unfortunately, the early graft loss rate has not improved over the last 30 years. Even in recent reports, the technical failure rate due to thrombosis was 5~10%.
First of all, we should understand the mechanism of thrombosis. In physiologic condition, the portal vein flow consists of the returning venous flows from the small intestine, colon, spleen, and pancreas. However, the venous flow of graft pancreas is made from only the graft pancreas. The low flow venous system must have the tendency of thrombosis, thus the graft pancreas in inherently thrombogenic.
The resistance to flow in small tubes was described by G. Hagen and J. Poiseuille. They found that resistance to flow is a function of the inner radius of the tube (r), the length of the tube (L), and the viscosity of the fluid. Their observations are expressed in the following equation, known as the Hagen-Poiseuille equation:
Q= ∆P x (πr⁴/8μL)
R= 8μL/πr4
This principle is also consistent with the results observed in clinical practice. Wider and shorter anastomoses are better for maintaining blood flow. The size of the opening is more important than the length according to the equation above.
We performed 60 cases of pancreas transplant (11-SPK or SPLK, 14-PAK, 34-PTA, and 1-Pancreas After Liver transplant) in Pusan national university Yangsan hospital, Korea, since 2015. There is no thrombotic graft loss in our cases.
Most of our cases were performed with venous drainage to vena cava and duodenal exocrine drainage. Vena cava had the privilege of preventing thrombosis because it was wide enough to make the bigger opening for anastomosis.
The venous anastomotic technique was evolved from the direct anastomosis (n=8). Then we did a Diamond-shaped patch anastomosis (n=13). After that, the fence angioplasty with using vena cava graft was applied to 31 cases. And finally, we have been performing the venous anastomosis with aortic interpositional graft (n=8).
The conventional or low molecular heparin was used for the prevention of thrombosis in first 40 cases of transplant. However, we do not use any heparin anymore neither in the intraoperative nor postoperative periods.
We always checked the 0 day CT angiography for detection early thrombosis in all patients. There was some partial thrombosis in graft splenic vein or SMV. However, these partial thrombosis did have any effect to graft loss. And intraoperative Doppler ultrasound was helpful for evaluation of the blood flow.
The average cold ischemic time for pancreatic graft was only 298.6 minutes. This short cold ischemic time may contribute to no thrombosis.  
In conclusion, for the prevention of thrombotic graft loss, we need to understand the mechanism of thrombus in graft pancreas and should do the best effort to make the wide venous anastomosis and maintain the venous flow. We would like to share our know-how with members of transplant society.