V bags for intravenous therapy. I.V. fluids provide the patient with life-sustaining fluids, electrolytes, and medications and offers the advantage of immediate therapeutic effects. Solutions used for I.V. fluid replacement fall into a broad categories of crystalloids and colloids. A solution administered into a vein through an infusion set that includes a plastic or glass vacuum bottle or bag containing the solution and tubing connecting the bottle to a catheter or a needle in the patient's vein.