I would like to point out that yes, we always use a 10cc syringe to flush our PICC's (per protocol and manufacturer's directions).
However, if you are attempting to draw from a PICC, it can sometimes be difficult, and you may think that your line is clotted. It can be positional and if you're having trouble getting blood return but can get it when your pt put their arm over their head it may in fact be a placement problem from the outset- always get an xray to check placement if this happens!
So, back to getting blood.. you can use a 5cc syringe BUT only to draw OUT of the picc. Not for infusing your flush! The 5cc syringe will exert more pressure on the line and usually will work. The other tip is to remove the end cap and luer lock your NS flush instead of using a blunt tip catheter. That works too. (usually)
Anyway, I just thought I'd throw out those tips I've learned from our IV team. They tend to get tired of us calling them because we believe our lines to be clotted when in fact it is an easy fix.
Yes, tPA might be needed to unclot a line, but it's not a usual occurence.