Blood sampling from midlines

I see the INS has a standard that discourages lab sampling from a "peripheral line" except at insertion time. I do not see anything specifically related to midlines. My lab tells me they can find no reason to prohibit drawing from a midline. I have heard and just accepted that we generally don't draw from midlines but I question why. I find no science. Can someone show me the sceince? I am updating policies and need to know what other data prevents lab draws from midlines.

A midline IV catheter should terminate before the axillary vein in the upper aspect of the upper arm. Therefore, though it is in a bigger vein than that which is in your forarms, it still doesn't have the blood flow that will yield a good return, in many cases. The material that the catheter is made from also plays a part. Some are softer than others and will collapse easier with gentle aspiration. 3fr midlines generally don't yield a brisk return and aspiration is discouraged. So, if you want to draw labs, place or have placed a 4fr midline (or ideally a PICC where blood flow is approx. 2 Liters/minute) they will yield better.

Drawing from a peripheral, except at the time of insertion becomes problematic as well. With small catheters and the diminished blood flow in our peripheral vasculature, blood sampling is not only unreliable through a catheter, but also one must take in to consideration what that negetive aspiration is doing to the endothelium of the tunica intima.

Hope that helps

DD