If one did not have in mind the meaning of Baruchat Atah Hashem Elokeinu in the first berachah of Shemone Esrei what should one do?
What about in any other berachah?
One should have intent for those words [silently] and continue from there.
See Shulchan Aruch O:C 101 and commentaries there. While one may repeat a portion of the bracha he is in, because of our general lack of kavana we generally do not repeat shem Hashem or complete brachos.
See Ishei Yisrael, Chapter 11 footnote 18 [pg. 96], in the name of the Chazon Ish, that one may have silent intent for the bracha he is presently holding in.