system
Given the following post, respond as if you're commenting on Reddit:
human
Why can't we replace hearts and lungs by pumping oxygenated blood though people?

 Like they do with bypass surgery. 

*Edit* In cases where people are waiting for new organs and such. Why can't it be a long term solution if a replacement isn't available immediately.
gpt
I took a master's in biomedical engineering and one of our professors who taught blood compatibility had actually worked on a lot of the early heart and lung machines. The two organs are indeed usually replaced together because the new artificial lung needs a good pressure difference to drive the blood through that you wouldn't want the patient's heart to have to maintain. 

He told us about the detrimental effects of the systems and I'll try to summarize. One is that the pumps lyse ("pop") the red blood cells. Another is platelet ("scab") accumulation on the device. Basically, the only thing blood won't try to scab up on is immunocompatible flesh.

These problems can be mitigated by constant fresh blood infusion and swapping out the machine, but infection is also a constant risk. The devices he worked on were used to treat acute, but not chronic, lung failure while the lungs would heal to take the job back over. IIRC, roughly one week.