what are you even talking about - for nerve blocks?? I don't think I've ever used 400mg lidocaine for anything. for pnb I don't generally repeat blocks although I have on occasion if it's been a few hours. I think this is just one of those clinical judgment situations as i'm not aware of any data on repeat doses of LA; with U/S I think most of us are using low enough volume these days that it doesn't become too much of a concern though