Sorry to hear about your dog. I've never put an animal 'to sleep' yet. Even though they say it's the humane thing to do, I don't know if I'd have the will to do it. I have had a few that I held on my lap when they were passing.
I unfortunetly have had to do the deed. My wife kids and I take in abused animals and ferrel cats, get them back to a worthy state, train them and find them perminent homes and to often they some times die in your lap or have to be taken out back to say goodbye.
It just so happens that this old 200 Lb. boy was my best friend and it's gonna be a hard thing to do.