NS is NS is NS: that is, Normal Saline is 0.9% Sodium Chloride solution, PERIOD, whether it is IV or in a pour bottle for irrigation.
I have always thought it silly that some nurses insist on using IV NS for cholangiograms--why?? It is, after all, just going into the common duct--part of the GI system. They never have a rationale as to why they think it is somehow "better" to use IV NS. They always say, stubbornly "That's just the way I've always done it," or "how we've always done it here." Whatever.
Now, if you are INJECTING contrast media for an ARTERIOGRAM, of course you would want to use IV NS, as you would to flush an IV or arterial line, or to give an IV push or piggy-back med--
But, if you are irrigating a harvested vein for implantation (i.e., a saphenous vein graft to be used during a CABG) it really makes no difference if you use IV NS or pourable irrigation NS, to which you have added the appropriate amount of Heparin.
I think some people just prefer to use pre-Heparinized IV NS already added (like the one we use to set up art lines) simply because it saves the step of drawing up your own Heparin. But then, you have to add a transfer jet to the bag, so that's an extra step you would'nt have with pouring out of a bottle--
I think it makes sense to do whatever is the most cost effective and/or most time efficient at your hospital--even if you work at an HMO or a military hospital, the extra costs have to be borne by SOMEONE--