What's the worst that can happen if you don't aspirate?

[mass junkie]

Ok maybe im stupid or I missed something but if your aspirating to see if you hit a vein what are you looking for? im guessing the only thing it could be is blood but arent you gonna get blood regardless?

[johnsomebody]

No, in my experience there's a huge dif -when you hit a vein you get a big plume of blood rushing into the syringe as soon as you start to aspirate .
Normally, you should only get at most a couple air bubbles, no matter how hard you pull.

Here's a great pdf on how to inject Red Ketchup posted elsewhere -it explains how to aspirate on page 3 but doesn't get into the why...
http://www.breastcancerprofessional...onc/nursing.pdf