What is the fundamental limitation of static cold storage regarding organ viability that machine perfusion aims to mitigate?

The fundamental limitation of static cold storage regarding organ viability is its inability to provide active oxygen and nutrient delivery or to actively remove accumulating metabolic waste products. Static cold storage involves keeping an organ at low temperatures, typically on ice or immersed in a preservation solution, which significantly reduces the organ's metabolic rate. The metabolic rate is the speed at which the organ's cells perform chemical processes necessary for life. While reduced metabolism slows the consumption of limited oxygen and nutrients present within the organ and delays the accumulation of waste products, it does not stop these processes entirely. Over time, the static environment leads to a depletion of remaining oxygen and nutrients and a buildup of toxic metabolic byproducts. This progressive deprivation and accumulation cause ongoing cellular damage, known as ischemic injury, which is harm due to insufficient blood flow and oxygen. This continuous, albeit slowed, damage ultimately compromises organ viability, which is the ability of the organ to survive and function successfully after transplantation, limiting the time an organ can be preserved. Machine perfusion aims to mitigate this by actively circulating a specialized preservation solution through the organ's vasculature. This active circulation continuously supplies the organ with oxygen and vital nutrients, directly addressing the depletion issue, and simultaneously flushes away accumulating metabolic waste products. This dynamic delivery and removal process significantly reduces ischemic injury by sustaining cellular function more effectively, thereby extending the safe preservation time and improving overall organ viability.