I use a saline lock on all patients. Depending on the situation and need for fluids, I will attach a bag of fluids to the lock as necessary. I've just found it easier to not accidentally yank out the IV that way. Also, our primary receiving facility will accept labs drawn by EMS, so 90% of my patients that would get labs in the hospital will get labs drawn in the ambulance. Just makes it easier on my facility and keeps the nurses happy.