Eli5: how do organs about to be transplanted stay alive from the moment they are extracted til they are implanted
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There are various methods, but typically they involve cold temperatures. See keeping living cells near the freezing point of water (but not over) sends the cells into a hibernation like state. They will slow down the rate at which they consume their supplied energy. This means that the organ can still be alive for hours outside of the body.
We can actually see this in whole humans too. Extreme hypothermia can lower someone’s heart rate and breathing rate to near undetectable levels. Which is why doctors who are treating suspected hypothermia deaths can’t pronounce the patient as dead until they reach a certain temperature and it’s certain that their body is truly dead.
I had an instructor for wilderness first aid that was a medic on an antartic expedition. One day he flew out to rescue someone who fell down a crevasse (a deep crack in ice). It took hours for them to reach him safely to extract him. He had a major head injury, but had survived well past when a warm person would’ve died because his hypothermia essentially slowed his biological clock waaaay down. So they extracted him and airlifted him out. Unfortunately while warming him up in the helicopter, the patient passed, but it was remarkable he survived that long either way.
It depend on the organ and for how long it is being transported. Alive is a relative term though. Organs can generally be disconnected from blood vanes and nerves and therefore die but unless it decomposes it will just work again once it is connected back again. So keeping an organ usable is much about preventing decomposition. So keeping it cold, seal it from possible infectious sources, and protect it from physical damage. Very similar to how you keep food safe to eat.
There are [preservation solutions](https://www.sciencedirect.com/topics/medicine-and-dentistry/preservation-solution) and organ transport devices that pump the solutions around or through the organ, and also lower the temperature, to keep the organ alive. Depending on the organ, it can be kept alive for 24-48 hours.
Typically a (long) airplane transport may take up to 18 hours; if it’s within the US (NY to LA for example) 6-8 hours, international 14-18 hours. So these transplant solutions make it possible for the donor and the recipient to be in different cities.
And of course, to minimize the time, the transplant surgery team starts “opening up” the recipient while the transport team is in flight to get the organ. Liver transplant surgery for example can take 12+ hours, they have to cut the lower ribs to gain full access to the liver area, so the “prep time” is significant (6 hrs?) before the new organ is even needed to be inserted. So a surgery team gets started while the transport team goes to get the organ.
There is also mechanical perfusion, basically hooking up kidneys (or now lungs) to a pump and keeping fluids or air moving through them.
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