I know this conversation is several years old, but in case someone else needs the info I wanted to post here. I had a three week old chick just die of this last night - she we completely blown up like a balloon. I pricked the skin with a sterilized needle and was able to get the air out but it was too late. I think it might have been a dirty needle as she was inoculated at the hatchery as I could not find any sign of trauma on her. Poor little thing.
This link helped:
http://www.thepoultrysite.com/forums/showthread.php?t=9981
This link helped:
http://www.thepoultrysite.com/forums/showthread.php?t=9981