Normothermic machine perfusion (NMP) represents a notable advancement in organ preservation for transplantation. This technology maintains donor organs in a near-physiological state outside the body. It aims to improve organ quality and expand the pool of available organs, ultimately enhancing the success rates of transplant procedures.
Beyond Cold Storage
Traditional organ preservation relies on static cold storage (SCS), where organs are flushed with a cold preservation solution and then stored at low temperatures. This method reduces cellular metabolism, slowing down deterioration. However, SCS has inherent limitations, including restricted preservation times. This limited window increases the risk of ischemia-reperfusion injury, which occurs when blood flow is restored to the organ after a period of cold storage.
SCS also hinders the ability to assess organ viability before transplantation, as the cold temperatures suppress metabolic activity. This means that organs, especially those from extended criteria donors, cannot be thoroughly evaluated for their function. NMP addresses these challenges by shifting from a cold, static environment to a warm, dynamic one, allowing for continuous metabolic activity and functional assessment.
How Normothermic Machine Perfusion Works
NMP mimics the body’s natural environment for the organ. It involves continuously pumping a warm, oxygenated solution through the organ’s vascular system. This perfusate, which can contain red blood cells or oxygen carriers, also delivers essential nutrients like glucose, insulin, and amino acids, while removing metabolic waste products. The temperature is maintained at a physiological range, allowing the organ to remain metabolically active.
Key components of an NMP system include a perfusion pump to circulate the solution, an oxygenator to supply oxygen and carbon dioxide, and a heat exchanger to regulate temperature. Monitoring systems continuously track parameters such as perfusate blood gas levels, lactate clearance, and glucose consumption, providing insights into the organ’s metabolic health and function. Some systems, particularly for the liver, require dual pumps to manage the different flow and pressure requirements of distinct vessels like the portal vein and hepatic artery.
Organs Benefiting from Normothermic Perfusion
NMP has shown promise across various organ types. For kidneys, NMP can improve immediate function rates and potentially reduce delayed graft function, particularly for organs from deceased donors. Measuring urine output during perfusion indicates kidney viability.
In liver transplantation, NMP can reduce the risk of early allograft dysfunction, post-reperfusion syndrome, and ischemic biliary complications. It enables assessment of liver function, such as bile production and lactate clearance, before surgery, allowing for better utilization of marginal livers.
For hearts, NMP systems have demonstrated the feasibility of preservation for up to 24 hours, a significant increase from cold storage, and allow for objective assessment of cardiac function, including echocardiograms. Lung transplantation was one of the first areas where normothermic perfusion was clinically applied, showing comparable results to traditional cold storage for high-risk donor lungs.
Transforming Organ Transplantation
NMP is transforming organ transplantation. This technology increases organ utilization rates, particularly for organs from extended criteria donors or those donated after circulatory death. By allowing for pre-transplant assessment and even reconditioning of organs, NMP helps expand the donor pool, leading to shorter waiting list times.
The enhanced preservation and viability assessment offered by NMP contribute to improved post-transplant outcomes, including better patient and graft survival rates. Studies have shown a decrease in complications such as ischemic biliary complications in liver transplants and a reduction in overall mortality. This technological advancement contributes to making organ transplantation safer and more successful.