New Guidelines Aim To Prevent Contrast Nephropathy

By Bruce Jancin 

CHICAGO -- Special precautions are warranted when the estimated glomerular filtration rate is below 60 mL/min per 1.73 m2 in a patient due to receive iodinated contrast media for an imaging procedure, according to a new report on contrast-induced nephropathy issued by an international multidisciplinary expert consensus panel.

Among the recommended precautionary measures are more aggressive hydration than has often been the norm, withdrawal of all nephrotoxic drugs, a 100-mL ceiling on contrast volume, and preferential use of nonionic iso-osmolar contrast, panel members said at the annual meeting of the Society for Cardiovascular Angiography and Interventions.

Contrast-induced nephropathy (CIN) is the third most common cause of hospital-acquired renal failure, leading to longer hospital stays and worse clinical outcomes, including dramatically greater short-term and 1-year mortality. CIN is expected to become a worsening problem for cardiologists, nephrologists, and radiologists in the next few years because of anticipated steep growth in the use of 64-slice CT scanners in addition to the steady rise in imaging-guided interventional procedures.

The panel identified the two major risk factors for CIN as preexisting renal dysfunction and diabetes. Diabetes multiplies the risk at all levels of renal dysfunction. Other CIN risk factors are volume depletion, use of nephrotoxic drugs, periprocedural hemodynamic instability, anemia, hypoalbuminemia, and heart failure.

"In a patient with multiple risk factors, expect CIN rates of 20%-50% and rates of acute renal failure requiring dialysis of around 15%. And very importantly, make sure that's reflected in your consent process. CIN isn't a small-risk event," cautioned Dr. Peter McCullough, a cardiologist at William Beaumont Hospital, Royal Oak, Mich.

Knowing a patient's EGFR is central to risk assessment for CIN. The College of American Pathologists now recommends that laboratories routinely provide EGFR data so physicians don't have to do the laborious calculation themselves. But a show of hands indicated only about one-half of the audience now receives an EGFR along with a serum creatinine measurement from their hospital laboratory.

The consensus panel reviewed nearly 900 published papers in its deliberations. Here are the panel's other key evidence-based recommendations:

1. Hydration. The CIN probability in at-risk patients is reduced by adequate intravenous hydration with isotonic crystalloid at 1.0-1.5 mL/kg per hour for 3-12 hours before the procedure and 6-24 hours afterward. Oral hydration isn't as good as intravenous. While physicians at William Beaumont switched from normal saline to sodium bicarbonate on the basis of one small favorable trial, either isotonic fluid is acceptable for now, Dr. McCullough said.
2. Administration. Intravenous administration of iodinated contrast appears to pose less risk of CIN than intraarterial contrast. Additional randomized trials addressing this issue are under way.
3. Medium. Nonionic iso-osmolar contrast medium (iodixanol [Visipaque]) shows the lowest risk for CIN and is the preferred agent in patients with chronic kidney disease and diabetes. In clinical trials, CIN rates in high-risk patients given iodixanol have consistently been in the 3% range.
4. Adjunctive treatment. No adjunctive pharmacologic or mechanical treatment is of proven efficacy in reducing CIN risk, including the widely used acetylcysteine (Mucomyst). "This is going to disappoint you, but we looked at the literature very, very carefully. There are dozens and dozens of trials of adenosine, prostaglandins, acetylcysteine. Nothing meets the grade of proven efficacy," Dr. McCullough said.
5. Urgent care. In the setting of an emergency procedure where the EGFR or serum creatinine may not be known, the benefit of immediate imaging outweighs the value of waiting for a measurement. An example of this is primary percutaneous coronary intervention for acute MI.
6. Threshold. No apparent threshold effect is seen for iodinated contrast volume.While there is good evidence that contrast volumes in excess of 100 mL are associated with higher CIN rates in at-risk patients, as little as 30 mL can cause CIN and need for dialysis in very-high-risk patients.
7. Nephrotoxic drugs. Discontinue nephrotoxic drugs about 3 days before the procedure in patients with an EGFR below 60 mL/min. This includes NSAIDs and metformin, which create a risk of potentially fatal lactic acidosis should the kidneys go into failure. "Metformin is absolutely contraindicated,"Dr. McCullough said.