Radiocontrast removal by dialysis membranes

The use of iodinated contrast media in patients with end-stage renal disease

Iodinated contrast agents are well tolerated in ESRD patients. Certain types of ICM, i.e., LOCM and the nonionic agents are associated with better safety profiles. Current available evidence, although not optimal, does not support the need for additional hemodialysis for ICM removal to preserve residual renal function or to treat other potential toxicities of ICM. However, limiting exposure to ICM is a prudent measure in ESRD patients given ICM’s potential toxicity; close monitoring of patients with poor cardiac function is also recommended in subjects receiving higher doses of ICM, especially those receiving HOCM.

Iodinated contrast media and the role of renal replacement therapy

Iodinated contrast media are among the most commonly used pharmacologic agents in medicine. Although generally highly safe, iodinated contrast media are associated with several adverse effects, most significantly the risk of acute kidney injury, particularly in patients with underlying renal dysfunction. By virtue of their pharmacokinetic characteristics, these contrast agents are efficiently cleared by hemodialysis and to a lesser extent, hemofiltration. This has led to research into the capacity for renal replacement therapies to prevent certain adverse effects of iodinated contrast. This review examines the molecular and pharmacokinetic characteristics of iodinated contrast media and critically analyzes data from past studies on the role of renal replacement therapy to prevent adverse effects of these diagnostic agents.

The role of extracorporeal blood purification therapies in the prevention of radiocontrast-induced nephropathy

Radiocontrast-induced nephropathy (RCIN) is a common and potentially serious complication following diagnostic and therapeutic cardiology procedures using radiocontrast media. The first and most important step in reducing the likelihood of RCIN is to identify patients at risk, by medical history and measurement of serum creatinine concentration to allow calculation of estimated glomerular filtration rate (GFR). Extracorporeal blood purification effectively removes radiocontrast media from the circulation. Periprocedural extracorporeal blood purification (hemodialysis or continuous renal replacement therapy) does not reduce the incidence of RCIN compared with standard medical therapy, and cannot be recommended at this time. The potential benefit of continuous venovenous hemofiltration published by a single center should be confirmed with further studies before it can be recommended or disregarded, and higher doses of continuous renal replacement therapy may also merit further investigation.

Preventing complications of radiographic contrast media: is there a role for dialysis?

Nephrologists are often called upon to provide hemodialysis to remove radiographic contrast media in patients with chronic kidney disease (CKD)--usually but not exclusively, those with end-stage renal disease. The reasons for this request vary from concerns over the volume load associated with the administration of a hyperosmolar solution, to the renal and extra-renal toxicities of the contrast itself. Simple calculations demonstrate that the increase in extracellular volume after a typical contrast load is minimal. Data supporting the extra-renal toxicity of contrast in patients maintained on dialysis are lacking. Iodinated contrast agents have molecular weights of 700-1500. This relatively small size as well as their lack of protein binding makes them well suited for removal with extracorporeal renal replacement therapies. Thus, provision of hemodialysis immediately following a contrast load is often utilized in an attempt to prevent further renal damage in patients with advanced stages of CKD. A number of trials have failed to demonstrate that this maneuver is effective. Hemofiltration (HF) has been reported to decrease the risk of acute renal failure in patients with CKD receiving a contrast load, but the studies are methodologically flawed. Therefore, there is currently no sound basis for routinely recommending hemodialysis (or HF) in patients at high risk for contrast media-associated complications.

Dialysis and iodinated contrast media

Contrast media are excreted mainly by glomerular filtration. There is thus, a significant correlation between both body and renal clearances of contrast media and glomerular filtration rate, and their renal excretion will be delayed in patients with renal insufficiency. Contrast media can be efficiently removed from blood by hemodialysis (HD). Since most contrast media are middle-sized molecules, the main factors potentially influencing their removal by HD are blood flow, membrane surface area, molecular size, transmembrane pressure, and dialysis time. Peritoneal dialysis is also effective in removing contrast agents from the body but takes longer than HD. Dialysis immediately after radiographic contrast studies has been suggested for two groups of patients. Those on chronic HD and those at very high risk for contrast nephropathy. Three studies have examined the necessity of immediate dialysis after intravascular injection of contrast media in chronic HD patients; the authors found no evidence that it is effective at preventing contrast nephropathy. The reasons why HD treatment was not beneficial in those three studies are not known. Perhaps, the rapid onset of renal injury after administration of contrast media is one answer. It is also possible that HD per se was nephrotoxic and might have offset the beneficial effect of the removal of contrast media. Marenzi et al. randomized 114 consecutive patients with chronic renal failure undergoing coronary interventions to either hemofiltration in an intensive care unit or isotonic saline hydration. The authors concluded that periprocedural hemofiltration given in an intensive care unit setting appears to be effective in preventing the deterioration of renal function due to contrast agent induced nephropathy and is associated with improved in-hospital and long term outcomes. The concentration of contrast media can effectively be reduced by HD and peritoneal dialysis. HD does not offer any protection against contrast media induced nephrotoxicity. Hemofiltration may decrease the risk of contrast induced nephropathy and have some long-term benefits, but additional studies are needed to better define the appropriate population for this treatment.

Removal of contrast media by different extracorporeal treatments

BACKGROUND

Although the capability of extracorporeal treatments after administration of contrast media to prevent radiocontrast-induced nephropathy is controversial, haemodialysis is performed in many institutions after radiographic procedures. There are conflicting reports on the efficacy of different dialysers and treatment modalities to remove contrast media.

METHODS

We compared the contrast medium-removing ability of different extracorporeal treatments in a randomized trial. Thirty-nine patients on chronic renal-replacement therapy or with chronic renal failure were randomized to receive low-flux haemodialysis (Low-HD, n=10), high-flux haemodialysis (High-HD, n=10), online haemodiafiltration (HDF, 10 litre substitution, n=10) and online haemofiltration (HF, 18 litre substitution, n=9) after administration of contrast medium during routine radiological procedures. Plasma concentrations of contrast medium (iopromide or iomeprol) were measured by energy-dispersive X-ray fluorescence analysis.

RESULTS

The extraction ratio for contrast media was 0.64+/-0.1 for Low HD (P<0.05 vs. High-HD and vs. HDF), 0.74+/-0.1 for High-HD (P<0.05 vs. HF), 0.81+/-0.1 for HDF (P<0.05 vs HF), and 0.62+/-0.1 for HF. Mean extracorporeal plasma clearances were 82+/-2 for Low-HD (P<0.05 vs. High-HD and vs HDF), 100+/-2 for High-HD, 115+/-4 for HDF (P<0.05 vs. HF), and 86+/-5 ml/min for HF.

CONCLUSIONS

We conclude that HDF and High-HD remove contrast media more effectively than Low-HD and HF during the time of each treatment session. However, whether this is also true for the overall elimination of contrast media by these different procedures needs to be addressed in future studies, by a precise assessment of the drug time course after the session.

Elimination of low-osmolality contrast media by hemodialysis

PURPOSE

To compare the dialyzability and safety of 2 types of low-osmolality contrast media administered to end-stage renal failure patients maintained on regular hemodialysis.

MATERIAL AND METHODS

Of 44 CT examinations, iohexol was used in 22 and ioxaglate in the other 22. Adverse reactions and hemodynamic changes were recorded. Thirty minutes after the beginning of CT investigation, hemodialysis was commenced. Elimination rate and clearance of the contrast media were measured as indices of their dialyzability.

RESULTS

After 4 hours of hemodialysis, 78.4+/-6.5% of iohexol and 72.4+/-6.0% ioxaglate were eliminated. Clearance of iohexol was higher than that of ioxaglate at all sampling times. No severe hemodynamic change nor adverse reaction were observed. Minor reactions were more frequently observed in the ioxaglate group.

CONCLUSION

Iohexol, a nonionic monomeric contrast medium, is more advantageous for hemodialysis patients than ioxaglate, an ionic dimeric contrast medium.