CO2 DIGITAL ANGIOGRAPHY - A SAFER CONTRAST AGENT FOR RENAL VASCULAR IMAGING

Although the new nonionic contrast agents are safer than ionic agents, renal insufficiency and even death still occur occasionally. Therefor e, we have explored the use of carbon dioxide (CO2) as an alternative angiographic contrast agent used in combination with digital subtracti on angiography. Clinical observations have been made in over 800 patie nts. The images obtained are of equivalent diagnostic quality compared with those using conventional iodinated contrast agents. Recent advan ces in imaging, including ''stacking,'' provide images comparable with iodinated contrast. Very small vessels, equivalent to third-order bra nches of the renal artery, can be imaged satisfactorily with CO2. Occa sional studies with CO2 yield information not apparent with iodinated contrast agents, including excellent visualization of arteriovenous sh unts, collateral circulations, malignant tumors, and minute amounts of arterial bleeding. Many of the advantages and disadvantages of CO2 de rive from its special physical and chemical properties. The advantages include no allergic potentiation and no renal metabolism of CO2, beca use CO2 is cleared by the lungs and does not recirculate. Other advant ages include delivery by very small catheters because of the low visco sity of CO2, minimal discomfort on injection, and very low cost. Howev er, the low-density and compressibility of CO2 poses some special prob lems. Imaging requires digital subtraction angiography with electronic enhancement and injections require an experienced investigator and, i deally, a dedicated CO2 injector. The dedicated CO2 injector provides calculated, controlled dosing and rates for injection, while excluding the possibility of air contamination. The buoyancy of CO2 inhibits go od filling of dependent vessels. Accordingly, CO2 does not normally pr oduce good nephrographic images, although proximal renal arteries are normally shown clearly. Experimental studies in dogs, whose renal arte ries have been injected repeatedly with very large doses of CO2, demon strate only transient changes in renal blood flow and no endothelial c ell damage. However, these studies also showed clearly that renal isch emia can occur due to a ''vapor lock'' phenomenon if the kidney is pos itioned vertically above the injection site, and recurrent injections are given without time for absorption of the arterially delivered CO2 boluses. Uncontrolled studies in over 800 patients have confirmed that CO2 likely has a very low renal toxicity. At the University of Florid a, CO2 is the radiologic contrast agent of choice in patients with ren al insufficiency, especially those with diabetes melitus, and in those with pre-existing allergy to iodinated contrast agents. Further contr olled clinical studies are required to define the true clinical utilit y and safety of CO2 compared with conventional radiologic contrast age nts. (C) 1994 by the National Kidney Foundation, Inc.