Noninvasive Test Links Pre-Angiography Fluid Volume to Later Kidney Damage

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A noninvasive method for measuring fluid status in patients before coronary angiography has been shown to predict the development of contrast-induced acute kidney injury (AKI), reports a paper published online February 12, 2014, ahead of print in the Journal of the American College of Cardiology. It has yet to be seen, however, whether the tool can be used to individually tailor hydration strategies.

Mauro Maioli, MD, of New Prato Hospital (Prato, Italy), and colleagues performed bioimpedance vector analysis (BIVA) to assess preprocedural fluid volume in 900 consecutive patients with stable CAD.

BIVA, a bedside test performed by nursing staff, is typically used to monitor the overall fluid volume of patients on dialysis or with heart failure. According to the study authors, it correlates well with the effective intravascular volume.

Low Fluid Triples Risk

Contrast-induced AKI (defined as: an increase in serum creatinine ≥ 0.5 mg/dL above baseline within 3 days) occurred at a rate of 6.0%. Patients with the complication tended to be older or female and have comorbidities including diabetes, hypertension, anemia, and advanced congestive heart failure. They had higher baseline serum creatinine levels and poorer creatinine clearance.

On BIVA, the resistance/height (R/H) ratio was higher and impedance/height (Z/H) vector was longer in patients who subsequently developed AKI. Both parameters indicate lower fluid volume (table 1).

Table 1. Preprocedural BIVA Parameters

Separated into quartiles of R/H ratio, patients with the most fluid depletion had nearly a threefold higher risk of developing contrast-induced AKI versus those with higher total body water (OR 2.9; 95% CI 1.1-5.5; P = 0.002).

ROC analysis identified the optimal R/H ratio for predicting kidney damage: 380 Ohm/m for women and 315 Ohm/m for men. R/H ratio, as either a continuous or categorical variable, independently predicted the development of contrast-induced AKI and “moderately” enhanced the ability to define risk when added to the Mehran risk score, the researchers report.

Too Early for Clinical Use

Despite the strong link observed between baseline fluid status and subsequent kidney damage, Dr. Maioli and colleagues caution that before the test “can be recommended for routine [clinical] use, additional studies will be needed to establish more precisely the worth of BIVA-guided monitoring in the prevention of CI-AKI.”

Two outside sources interviewed by TCTMD strongly agreed.

Somjot S. Brar, MD, MPH, of Kaiser Permanente (Los Angeles, CA), said in an e-mail that “incorporation of a noninvasive assessment of fluid status may be a novel adjunct to CI-AKI risk prediction.”

It remains to be seen, though, whether this tool adds to the already established predictive value of clinical characteristics, he commented. “These data are encouraging and suggest such a benefit may exist, but the magnitude of the incremental benefit is less clear and needs to be clearly delineated before such measures should be routinely performed,” Dr. Brar said.

Richard Solomon, MD, of the University of Vermont (Burlington, VT), told TCTMD in a telephone interview that the study mostly confirms the known association between fluid status and kidney damage. “There’s a lot more work to be done to figure out how to use this in a way that could potentially mitigate the adverse effects of the contrast,” he stressed.

An Alternative to Invasive Tests

“In patients undergoing invasive cardiac procedures,” Dr. Brar said, “accurate measurements of intravascular volume status can be easily obtained from intracardiac pressures at the time of the procedure. This information can be used to safely guide more aggressive intravascular volume expansion.” Such a concept is being explored by the POSEIDON trial, for which he serves as principal investigator.

Though, “having a non-invasive surrogate for the invasive intracardiac measurement, in particular for patients exposed to contrast for other common procedures such as CT imaging, may be of significant benefit,” Dr. Brar suggested, adding that the safety and superiority of such an approach can only be shown by randomized controlled trials.

According to Dr. Solomon, BIVA is “fairly easy to do and noninvasive, but it’s quite variable. [Testing] the same patient on multiple days, you get different [results].

“You have to be very careful how the patient is lying down,” he continued. “In the paper, they cite the usual recommendations [about] the feet apart and the arms apart. These are all things you have to pay a lot of attention to. When it gets out into the real world, the sensitivity of this may go down.”

Study Details

All patients received the contrast medium iodixanol during angiography. In addition, they were given standard IV hydration (0.9% sodium chloride at 1 mL/kg/h for 12 hours before and after; the rate was halved for those with LVEF < 40% or NYHA class III-IV) as well as oral N-acetylcysteine (600 mg twice daily on the day before and the day after angiography).

Source:

Maioli M, Toso A, Leoncini M, et al. Pre-procedural bioimpedance vectorial analysis of fluid status and prediction of contrast-induced acute kidney injury. J Am Coll Cardiol. 2014;Epub ahead of print.

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