Patients with renal impairment and/or contrast allergies pose a challenge with regard to diagnostic evaluations. CO 2 may serve as a suitable alternative intravascular contrast agent in these patients with arteriographic applications, including evaluation of peripheral vascular disease, and venographic applications, such as transjugular intrahepatic portosystemic shunt procedure, to name a few. Unique properties of CO 2, such as low viscosity, lack of an allergic reaction, and renal toxicity, have afforded it its diagnostic capabilities. However, certain properties of CO 2 also pose a technical challenge in terms of its delivery. Although it remains a relatively safe alternative contrast agent, potential adverse effects have been reported and exist. © 2011 Mosby, Inc.