I think for a regular IV it actually takes a lot of air in the line, but with a central line it's a lot more dangerous.

I'm not an expert and I didn't check my info but I did ~~stay at a hoiday inn express~~ get an IV every month for the past decade, and in years past have discussed these things with seasoned nurses as I watched air bubbles of various sizes enter my vein.

That's some genuine folk wisdom for ya, lol.