Long term TPN does cause liver problems. My son was on it for 2 years and suffered liver failure. So, it all depends how how long he was on it. You may want to get some bloodwork done to determine if there was any damage to his liver. I hope he is doing well now. Take care....
I've had to have TPN a couple of times due to some gastrointestinal issues, but they've only been short terms (no more than two weeks at a time). My doctor told me that TPN is generally safe, but as with any medical intervention, there are some risks. One of them is gall bladder problems because with the TPN the gastro tract is not being used for digestion. Another one is the possibility of liver failure. Neither of these is a big risk, the they are a risk nontheless. Actually, more of the complications from TPN arise from the catheter used to deliver the nutrition rather than the feedings themselves.
I hope your son is doing better.