How do I uniquely id a row from within a trigger

I have a trigger set up to run whenever a insert occurs on a table. This table is an audit table, therefore there is no unique key identifiers. My question is how do I uniquely id the row just inserted to the stored procedure which is called by the trigger. It appears that the system field rowid is not available from within the trigger. There are too many fields to pass them all to the stored procedure. I am considering the addition of a timestamp field, but I worry about uniqueness (> 30 users will be using this system at any given time). I would appreciate any advice on this matter. Andy Sirotta