|Classification and external resources|
Contrast-induced nephropathy is defined as either a greater than 25% increase of serum creatinine or an absolute increase in serum creatinine of 0.5 mg/dL after percutaneous coronary intervention (PCI) using a contrast agent. Despite extensive speculation, the actual occurrence of contrast-induced nephropathy in other patient populations has not been demonstrated in the literature.
A new definition of contrast nephropathy in patients undergoing percutaneous coronary intervention was recently proposed by Harjai, et al. This tripartite definition classifies contrast nephropathy as grade 0 (serum creatinine increase <25% above baseline and <0.5 mg/dL above baseline), grade 1 (serum creatinine increase >/=25% above baseline and <0.5 mg/dL above baseline), or grade 2 (serum creatinine increase >/=0.5 mg/dL above baseline). This classification is prognostic of long-term outcomes of patients after percutaneous coronary intervention. Patients with grade 2 nephropathy had the worst outcome while those with grade 0 nephropathy had the best outcome on long-term follow-up.
To minimize the risk for contrast-induced nephropathy, various actions can be taken if the patient has predisposing conditions. These have been reviewed in a meta-analysis. A separate meta-analysis addresses interventions in for emergent patients with baseline renal insufficiency.
Three factors have been associated with an increased risk of contrast-induced nephropathy: preexisting renal insufficiency (such as Creatinine clearance < 60 mL/min [1.00 mL/s] - online calculator), preexisting diabetes, and reduced intravascular volume.
- Systolic blood pressure <80 mm Hg - 5 points
- Intraarterial balloon pump - 5 points
- Congestive heart failure (Class III-IV or history of pulmonary edema) - 5 points
- Age >75 y - 4 points
- Hematocrit level <39% for men and <35% for women - 3 points
- Diabetes - 3 points
- Contrast media volume - 1 point for each 100 mL
- Renal insufficiency:
- Serum creatinine level >1.5 g/dL - 4 points
- 2 for 40–60 mL/min/1.73 m2
- 4 for 20–40 mL/min/1.73 m2
- 6 for < 20 mL/min/1.73 m2
5 or less points
- Risk of CIN - 7.5
- Risk of Dialysis - 0.04%
- Risk of CIN - 14.0
- Risk of Dialysis - 0.12%
- Risk of CIN - 26.1*
- Risk of Dialysis - 1.09%
- Risk of CIN - 57.3
- Risk of Dialysis - 12.8%
Choice of contrast agent
The osmolality of the contrast agent was previously believed to be of paramount importance in contrast-induced nephropathy. Today it has become increasingly clear that other physicochemical properties play a greater role, such as viscosity. Attention should be paid to use contrast agents of low viscosity. Moreover, sufficient fluids should be supplied to limit fluid viscosity of urine. Modern iodinated contrast agents are non-ionic, the older ionic types caused more adverse effects and are not used much anymore.
One study has suggested that iso-osmolar, nonionic contrast media may be superior to others. However, several subsequent studies failed to confirm this. A large scale study strongly suggested that an iso-osmolar contrast media more often cause clinically relevant kidney failure than a low-osmolar contrast agent.
Hydration with or without bicarbonate
Administration of sodium bicarbonate 3 mL/kg per hour for 1 hour before, followed by 1 mL/kg per hour for 6 hours after contrast was found superior to plain saline on one randomized controlled trial of patients with a creatinine of at least 1.1 mg/dL (97.2 µmol/L) . To make the solution, the study used 154 mL of 1000 mEq/L sodium bicarbonate to 846 mL of 5% dextrose. This is approximately three 50 ml ampules of bicarbonate in 850 ml of water with 5% dextrose. This was subsequently corroborated by a multi-center randomized controlled trial, which also demonstrated that IV hydration with sodium bicarbonate was superior to 0.9% normal saline. However, additional confirmatory trials with sodium bicarbonate are needed because the largest trial to date showed no benefit of sodium bicarbonate over normal saline . The renoprotective effects of bicarbonate are thought to be due to urinary alkalinization, which creates an environment less amenable to the formation of harmful free radicals.
Alternatively, one randomized controlled trial of patients with a creatinine over 1.6 mg per deciliter (140 µmol per liter) or creatinine clearance below 60 ml per minute used 1 ml/kg of 0.45 percent saline per per hour for 6–12 hours before and after the contrast.
Adenosine antagonists such as the methylxanthines theophylline and aminophylline, may help although studies have conflicting results. The best studied dose is 200 mg of theophylline given IV 30 minutes before contrast administration.
N-acetylcysteine (NAC) 600 mg orally twice a day, on the day before and of the procedure if creatinine clearance is estimated to be less than 60 mL/min [1.00 mL/s]) may reduce nephropathy. A randomized controlled trial in 2006 found that higher doses of NAC (1200 mg IV bolus and 1200 mg orally twice daily for 2 days) benefited (relative risk reduction of 74%) patients receiving coronary angioplasty with higher volumes of contrast.
Since publication of the meta-analyses, two small and underpowered negative studies, one of IV NAC and one of 600 mg give four times around coronary angiography, found statistically insignificant trends towards benefit.
Some authors believe the benefit is not overwhelming. The strongest results were from an unblinded randomized controlled trial that used NAC intravenously. A systematic review by Clinical Evidence concluded that NAC is "likely to be beneficial" but did not recommend a specific dose. One study found that the apparent benefits of NAC may be due to its interference with the creatinine laboratory test itself. This is supported by a lack of correlation between creatinine levels and cystatin C levels.
A clinical trial from 2010, however, found that acetylcysteine is ineffective for the prevention of contrast-induced nephropathy. This trial, involving 2,308 patients, found that acetylcysteine was no better than placebo; whether acetylcysteine or placebo was used, the incidence of nephropathy was the same — 13%.
Patients with chronic renal insufficiency and a creatinine over 309.4 µmol/L (3.5 mg.dl) who have elective coronary catheterization, a randomized controlled trial found benefit from prophylactic hemodialysis
Other pharmacological agents, such as furosemide, mannitol, dopamine, and atrial natriuretic peptide have been tried, but have either not had beneficial effects, or had detrimental effects. Of course, limiting the total contrast volume also aids greatly in reducing the incidence of contrast nephropathy.
While there are currently no FDA-approved therapies for Contrast Induced Nephropathy, two therapies are currently being investigated. CorMedix, Inc. is currently in the latter part of Stage II clinical trials with approved Phase III Special Protocol Assessment for CRMD001 (unique formulation Deferiprone) to prevent Contrast-Induced Acute Kidney Injury (AKI) and to slow progression of Chronic Kidney Disease (CKD). Dosing trials began in June 2010 in the sixty patient trial.
PLC Medical Systems, Inc. has begun a Stage III clinical trial of RenalGuard Therapy to prevent Contrast-induced nephropathy. The therapy utilizes the RenalGuard System, which measures the patient's urine output and infuses an equal volume of normal saline in real-time. The therapy involves connecting the patient to the RenalGuard System, then injecting a small dosage of furosemide to induce high urine rates. RenalGuard Therapy has already been studied in two Italian studies, both of which found the therapy to be superior to the current standard of care.
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