Hi Russ, My brother in law in October had the same issue though he also lost a few fingers. the doctors did a good job with the reattachment but the big thing that helped him was PT. Have they set that up for your son? I am sorry to hear your bad news and pray that everything will be good. As for the hatch, I think too low is better than too high and I think 75 is good, I've read that under 60 is the problem.
Best Regards