1) The blessing of Yishtabach does not commence with the word “Baruch” as it is considered joined on to the blessing of Baruch She’amar, as both were decreed to be attached to the verses of praise, one before and the other after, and every “joined blessing” does not start with “Baruch”. The verses of praise said in the interim do not constitute a break between the two blessings. (Shulchan aruch 53)
2) Since Yishtabach is the blessing which finishes the verses of praise, if one did not say at least Baruch She’amar and Ashrei, he cannot say Yishtabach, and if he did say it, it will be considered a waste of a blessing. (ibid 52)
