ESRD patients are typically “hard sticks.”   The arm with the fistula is typically off limits (unless in emergency settings) and the other arm is either difficult to access or occasionally has an old fistula.

This issue came up recently and we all were left shrugging as to whether we were allowed to place peripheral IVs into old fistulas?

A dialysis fistula is a direct connection from artery to vein.  Because of that arterial pressure on the vein, it tends to balloon and can be seen clearly.  Unfortunately if you’re attempting to access an old fistula, there is a reason it is no longer being used. Generally stenosis or thrombosis.
Therefore, I propose the use of color Doppler when looking at the vein and liberal use of flushes to determine if the vein is still patent.  running the ultrasound up and down the vein and compressing as you go (like a DVT study) will also show you any occlusive clot living in your VOC (vein of choice).
In our case, we accessed the vein and got a that pristine PE study.  Would love to hear how yours turn out!