EDRN657

I've been doing ultrasound-guided IV's for a while now, and I feel like I'm fairly good at them. I am usually the go-to for difficult IV sticks, and very rarely miss (not bragging), however, lately it seems they are blowing after a few minutes of running. They draw back great when I initially place them and flush without difficult or causing pain, but about 200-300 mls of NS infusion later, the patient's are having pain in the area and I can no longer draw back. Are there any tips you can offer as to why this is happening or how to avoid it? I've never had any formal training; I've just picked it up through watching others and through practice. The only insight I could offer you, readers, is that it seems to always be the deep Basilic veins that blow, I use the 1.88" 20g or 18g IV caths, and I really don't think it's the catheter being pulled back out of the vein. Any other suggestions?