Paper Title
Development of a Perfusion Scheme for Long-Term Preservation of an Liver Graft in an Experiment

Abstract
INTRODUCTION The method of machine perfusion of a liver transplant has been gaining popularity, justifying the hopes placed on it. Machine perfusion of the liver involves the creation of a biotechnical complex consisting of a graft and a perfusion apparatus. They are interconnected according to a certain scheme by artificial blood lines and accessories of the perfusion machine. The existence of a variety of perfusion schemes due to specific experimental or clinical needs. The aim of this study was to experimentally develop a perfusion scheme for long-term preservation of the liver outside the body by perfusion with normothermic oxygenated blood. MATERIAL AND METHODS A roller blood pump console was used to create a perfusion machine. Additional equipment included a standard pediatric oxygenator, venous and arterial filters, PVC and silicone lines. In the composition of the machine we included a converter of a constant flow into a pulsating (external pulsator) of our own design. In the perfusion scheme after the roller pump, the blood flow was divided into two streams. The first was sent to the oxygenator. Then, having passed the pulsator, the flow was fed through the aortic stump into the hepatic artery. The second flow was directed to the upper soft-walled tank. As an experimental model, 6 Caucasian sheep weighing up to 20 kg were used. Under general endotracheal anesthesia under conditions of thoraco-laparotomy, the liver was explanted along with a section of the caudal vena cava and aorta. The suprahepatic portion of the vena cava and the distal end of the aorta were ligated. Injection cannulas were inserted into the aorta and portal vein, and a draining cannula was inserted into the distal end of the vena cava. The cannulas were connected to the perfusion machine and perfusion of the organ was started. Sensors for monitoring the volume of blood flow, pressure, temperature, and blood oxygen saturation were located at different parts of the perfusion scheme. A venous filter was placed after the cannula of the vena cava, and an arterial filter was placed between the oxygenator and the pulsator. RESULTS AND DISCUSSION All experiments were carried out for 12 hours. The temperature of the perfusate was maintained within the range up to 37°C; volumetric blood flow in the portal vein averaged 450-500 ml/min; pressure was maintained within 12-24 mm Hg; the pulse rate in the arterial line did not exceed 100 beats/world; volumetric blood flow in the hepatic artery averaged 80-120 ml/min; the average pressure was maintained within 70 mm Hg. These parameters were maintained throughout the experiment. The division of the blood flow after the oxygenator made it possible to pump arterial, oxygenated blood in a pulsating flow into the organ, maintaining the planned volume of blood flow and pressure. At the same time, this made it possible to supply perfusate to a soft-walled reservoir located 50–70 cm above the perfused organ. So in the caudal vena cava, the pressure was maintained within the physiological norm. At the same time, the required level of perfusate for gravitational injection into the portal vein was stabilized in the soft-walled reservoir. CONCLUSION The developed scheme for machine perfusion liver preservation makes it possible to stabilize two blood flows (arterial and venous) of different characteristics during a prolonged experiment. Keywords - Liver Preservation, Machine Perfusion, Perfusion Scheme.