The Northcoast Medical Training Academy describes rolling veins as veins that move or roll from side to side, which makes drawing blood difficult. In order to prevent this, patients need to stay well-hydrated.
There are a few tricks to deal successfully with rolling veins while injecting medication or drawing blood, says the North Carolina Harm Reduction Coalition. The first is for professionals to use a thick tourniquet in order to prevent the vessels from moving. The second trick is to place the patient's arm against a flat surface. Fortis College advises professionals to place pressure firmly on the vein in order to anchor it before inserting a needle.
Some medical innovations also make it possible to deal with rolling veins. According to Wikipedia, there is a winged infusion set that makes it easier to access not just rolling veins, but fragile and hard-to-reach veins, as well. This special needle has flexible wings on either side where the medical professional places his fingers in order to anchor the device for precise placement. The needle is designed to be inserted at a shallow angle so that it is able to access rolling veins while simultaneously applying pressure to the veins with the wings.