how can this happen

If I am understanding you you replaced a PEG tube through the same tract and the tip of the PEG tube ended up in the lung (and by lung I am assuming you mean pleural space)?

I think that this would be almost impossible. The only way that I could conceive of it happening is that somehow the tract broke down and you went between the stomach and the abdominal wall then through the diaphragm. I have a hard time seeing this done with 6cm of PEG. If it was one of the mushroom types I have seen people perforate various organs with the trocar but a MIC type would be pretty much impossible.

David Carpenter, PA-C