By Jim Caridi
CO2 angiography can decrease both morbidity and mortality for patients, in certain clinical scenarios. For those driven by economics, the cost of 100cc of CO2 is approximately three cents. Its use is limited only by one’s imagination. So why is it not more widely used?
I had the privilege of training and working with Dick Hawkins, the father of CO2 angiography for over 25 years. During that time, I watched him perfect the use of CO2 as a vascular imaging agent in a multitude of clinical scenarios that many of us would never consider. In essence, its use is limited only by one’s imagination.
Saying that, I would like to start by stating that is not the quintessential contrast agent and that it does have limitations. It does, alone or in combination with liquid contrast, however, have a multitude of advantages that hands-down saves kidneys, prevents dialysis, affords treatment to a group of individuals that would otherwise be precluded, and aids in making a diagnosis that contrast would miss. Bottom line, it can decrease both morbidity and mortality, in certain clinical scenarios. Additionally, for those driven by economics, the cost of 100cc of CO2 is approximately three cents.
Considering its most famous indication, CO2 used in vascular imaging is non-nephrotoxic. When used instead of traditional iodinated liquid contrast, it reduces or eliminates contrast-induced nephropathy. Two major studies reported that hospital-acquired contrast-induced nephropathy increases mortality 22–34%, doubles the duration of the hospitalisation, and doubles to quadruples the one-, two- and five-year mortality of the patient. So, it has immediate and also long-term, devastating results. There are three major variables related to contrast-induced nephropathy. These are: route of delivery, underlying renal function, and total volume of contrast. Regardless of the many ways attempted to decrease contrast-induced nephropathy, including hydration and bicarbonate drip, the only variable that is easily addressed is the volume of contrast. In many instances, liquid contrast can be supplemented with CO2, eliminating liquid contrast completely; or at least, significantly reducing its volume.
The advantages of CO2 as an imaging agent do not stop with contrast-induced nephropathy. The attributes of CO2, especially its low viscosity, allow benefits that traditional contrast cannot provide. It is non-allergic, can be more readily administered through microcatheters, is more sensitive (2.5x) in the detection of bleeding, can visualise the portal vein for portal venous intervention with needles as small as 27 gauge, allows better visualisation of collateral and patent central veins in venous vasculopaths, permits central reflux so that proximal culprit lesions and anatomy can be evaluated without catheter withdrawal, and can also be used in routine diagnostic angiography and venography. Specific procedures in which CO2 is especially beneficial include: inferior vena cava filter placement, venography, angiography, transjugular intrahepatic portosystemic stent shunting, balloon-occluded retrograde transvenous obliteration (BRTO), portal vein embolization, routine renal stenting, renal transplant evaluation and intervention, endovascular aneurysm repair (EVAR), interventional oncology arterial interrogation, arterial bleeding, peripheral vascular intervention, and splenoportography. Recently, we have employed CO2 in urgent or emergent situations where a liver becomes available and the recipient’s portal vein patency is equivocal. These patients are often very ill with ascites and coagulopathy. In a matter of minutes, a 25–27 gauge spinal needle can be inserted into the liver parenchyma without correction of the ascites or coagulopathy. Ten to 20cc of CO2 will demonstrate patency or occlusion of the portal vein.
In my research for a recently-published guide to CO2 use, newer applications have included vascular CO2 for dyna CT, vertebroplasty, and nerve ablation. Other unique uses include angioscopy, and for the dissection of organs during ablative procedures.
So, why is CO2 vascular imaging not used more readily? The answer is fear, unfamiliarity and previous unwieldy, confusing, and time-consuming delivery systems. Although it seems preposterous, the same individuals performing meticulous complex procedures such as EVAR, TIPS, critical limb ischaemia, embolization, and more, are somehow uncomfortable using CO2. I have witnessed this in person with some of the redwoods of vascular interventional radiology. I attribute this first to the invisibility of CO2. Combine that with the previous delivery systems which required assembly, were unwieldy, and certainly labour-intensive to even use and even extremely qualified physicians were concerned about possible complications. If one compares, however, the reported incidence of significant complications from CO2, including the many unorthodox methods of delivery, they pale in comparison to the complications of iodinated contrast. During a key opinion leader conference in 2011, greater than 20,000 cases were performed by the attendees with only a handful of significant complications. So the reality is, despite confusing and cumbersome systems, CO2 can be used safely and effectively. This is especially true if a few easy principles are understood and employed when using it as a vascular imaging agent.
It is my hope that with education and the use of newer, faster, safer, more user-friendly delivery systems, CO2 as an imaging agent will become a more common utility vehicle in the vascular and interventional radiology garage. I expect this to translate into less contrast-induced nephropathy, better diagnosis, less-invasive procedures, and hopefully, less morbidity and mortality for our patients.
Jim Caridi is professor of Radiology, Tulane University Medical School New Orleans, USA. He has disclosed that he is instrumental in developing a new CO2 delivery system for which he has currently not received financial remuneration.