Heather Briscoe talks about thrombus.

Around 3% of our patients develop a thrombus due to having an IV access device in situ.

This is a significant number when we think that most hospitals with an IV Access Service of some sort will place upwards of 600 lines per year - and these are only the ones we know about. 

These are the ones that had symptoms severe enough to provoke investigation, usually those with a line longer than a cannula.