KDIGO Clinical Practice Guideline for Acute Kidney Injury
Dose/Volume of Contrast-Media Administration: Recommendations and Rationale

Dose/volume of contrast-media administration

• 4.3.1: Use the lowest possible dose of contrast medium in patients at risk for CI-AKI. (Not Graded)

Rationale

The correlation between the volume of contrast media administered and the risk of CI-AKI has been recognized. ⁴³³ In the vast majority of papers dealing with CI-AKI after coronary procedures, contrast-media doses are only expressed in volumes. The Work Group feels that such expression can be misleading, since commercially available contrast-media concentrations range from 140 to 400 milligrams of iodine per milliliter, a difference with almost a factor of 3. The Work Group recommends, therefore, that the dose of contrast medium should be better expressed in relation to both volume and concentration, e.g., grams iodine, which also directly relates to the diagnostic capacity, the primary purpose of the contrast medium. Such ‘‘double’’ expression would also facilitate the comparison between different studies on epidemiology and prognosis of CI-AKI.

It is well known that, when measuring the plasma clearance of a GFR marker (e.g., with the contrast medium iohexol), the AUC is directly related to the dose of iohexol and inversely related to the GFR. Thus, by mathematically estimating the AUC and knowing the injected iodine dose, the GFR can be calculated by dose ÷ AUC. Thus, AUC = dose ÷ GFR, and AUC is directly related to the systemic exposure of a drug, including the contrast medium, which, in turn, is mostly correlated with its efficacy and toxicity.⁴³⁴ An interesting experimental study⁴³⁵ investigated the correlation between the calculated dose to CrCl ratio and the experimentally measured AUC for the contrast agent iodixanol. The experimentally determined AUC data correlated highly with the dose:CrCl ratio. This ratio could thus be a rapid and accurate way to estimate AUC for an iodinated contrast medium, without the need for multiple blood samples.

A recent study by Nyman et al.⁴³⁶ in patients undergoing coronary angioplasty calculated the probability of CI-AKI (SCr rise > 0.5 mg/dl [ > 44.2 µmol/l] or oliguria/anuria) at various eGFR levels based on g-I (grams iodine)/eGFR ratios of 1:2, 1:1, 2:1, and 3:1. At a ratio < 1, the risk of CI-AKI was 3%, while it was 25% at a ratio ≥ 1. This, and other preliminary studies, indicate that a g-I/GFR ratio < 1 may be relatively safe in a patient without multiple risk factors.^436-438

Finally, the association between absolute and body weightand SCr-adjusted contrast-media volume, CI-AKI incidence ( ≥ 25% SCr increase), and clinical outcome was prospectively investigated in patients with acute MI.⁴³⁹ For each patient, the maximum contrast-medium dose was calculated according to the formula (5 x body weight [kg]) ÷ SCr, and the contrast-medium ratio—defined as the ratio between the contrast-medium volume administered and the maximum dose calculated—was assessed. Development of CI-AKI was associated with both contrast-medium volume and ratio. Additional radiological measures to reduce CI-AKI can be found in Table 16.