Usually organs for transplantation are harvested from patients who are declared brain-dead. And pathologists are sometimes called in to do frozen sections on liver and kidney in order to assess the degree of disease in these organs. F'rinstance, if a liver shows changes of hepatitis or cirrhosis, it won't be used. Similarly if a kidney contains too few glomeruli (the parts of the kidney that filter waste products from the blood), then it won't be transplanted.
Anyway, late last night one of my colleagues was called in to do such frozen sections. However, the patient wasn't brain-dead but rather in extremis and expected to die once removed from the mechanical ventilator. But the person started breathing on their own and didn't succumb as expected within an hour. The transplant team gave up and went home.
I found this whole scenario rather creepy and reminiscent of something out of a Robin Cook medical mystery novel (except his characters would make sure the intended donor was dead).