I'm sorry but you have the pathophys on this all wrong! We aren't worried about stroke from air in the line, we're concerned about air embolism. This can be caused by a pocket of air entering the right atrium/ventricle (prior to making it to the lungs) and either completely obstructing the blood flow to the lungs, and then subsequently the rest of the body, or lodging itself in the heart/lungs/brain of a pt. The "bubble" of air (and really its more a bolus than a bubble) can cause fatal arrhythmias even if it doesn't block off blood flow. The increased PA pressure created by an air bubble in the right side of the heart shuts off flow because the hearts circulation requires certain pressure gradients to function properly. Yes, the capillaries in the lungs can filter some of this, but it can also cause pulmonary edema from the excess pressure forcing the blood into the capillary beds and permanently damaging them.
It is true that the small bubbles in IV lines aren't enough to cause it, basically the entire IV tubing would have to be nothing but air to cause it in an adult PIV, but if you are using a central line or talking about a child, its far less air to cause a fatal rhythm or air embolism. Some documented cased with as little as 5ml causing problems in central lines.
That said, I don't worry about the little bubbles at all. If I've primed my tubing and there are some bubbles, I don't think twice. The other night I primed NS for what looked like was going to be rapid IV boluses to prevent my pt from crashing (pressures dropped from 110's to 50's in like 45sec) and I connected it to her PIV. I didn't give them because she came around on her own, but my charge nurse looked at my line (with less than two inches of air at the end) and said "well she didn't code but she would have if you infused that". I didn't argue with her at the time, but I knew she was wrong, because its sort of nursing "urban legend" that small bubbles of air will kill a pt. That portion of the line was maybe 1/2ml, and it was going to a PIV. Not losing any sleep over that one!
I have found that priming slowly makes all the difference. Once I started slowing down, I never had an issue with excessive bubbling.
Sorry for any spelling errors, I can't figure out how to get my spell check to work