Thank you dhb.
In my experience this procedure is really easy.
For a normal size person you shouldn't go more than 2 inch deep to find the vein. If you don't find it - means that the site of entry is wrong. Followinf this advice the chances of pneumothorax are 0...
This isn't a procedure to be done with US guidance...There isn't really to much space to place a probe and to control the needle in the same time.
The angle of approach is important too.