transaction identifier

I there, is it possible to identify the transaction running, when using a
pg/sql function?
Here is my problem:

I have a trigger in the database for one of my tables when I do an update. I
was trying, for all the rows affected when I'm doing an update, to send a
NOTIFY to my code. the problem is that I realize that if the NOTIFYs are
inside the same transaction, the database only sends one. What I'm doing is
having a auxiliar table where I insert the information that I consult when I
received a NOTIFY, and then after I read that information in my code I just
delete it. the problem is that I've Concurrency and I dont want to use
SELECT FOR UPDATE. If I had another row inside that auxiliar table
identifying the transaction I could distinguish the information and when I
delete it, according to the transaction id.

can you help ? Luis