Micronutrient and Amino Acid Losses During Renal Replacement Therapy for Acute Kidney Injury.

INTRODUCTION: Malnutrition is common in patients with acute kidney injury (AKI), particularly in those requiring renal replacement therapy (RRT). Use of RRT removes metabolic waste products and toxins, but it will inevitably also remove useful molecules such as micronutrients, which might aggravate malnutrition. The RRT modalities vary in mechanism of solute removal; for example, intermittent hemodialysis (IHD) uses diffusion, continuous veno-venous hemofiltration (CVVH) uses convection, and sustained low-efficiency diafiltration (SLEDf) uses a combination of these. METHODS: We assessed micronutrient and amino acid losses in 3 different RRT modalities in patients with AKI (IHD, n = 27; SLEDf, n = 12; CVVH, n = 21) after correction for dialysis dose and plasma concentrations. RESULTS: Total losses were affected by modality; generally CVVH >> SLEDf > IHD (e.g., amino acid loss was 18.69 ± 3.04, 8.21 ± 4.07, and 5.13 ± 3.1 g, respectively; P < 0.001). Loss of specific trace elements (e.g., copper and zinc) during RRT was marked, with considerable heterogeneity between RRT types (e.g., +849 and +2325 µg/l lost during SLEDf vs. IHD, respectively), whereas effluent losses of copper and zinc decreased during CVVH (effect size relative to IHD, -3167 and -1442 µg/l, respectively). B vitamins were undetectable in effluent, but experimental modeling estimated 40% to 60% loss within the first 15 minutes of RRT. CONCLUSION: Micronutrient and amino acid losses are marked during RRT in patients with AKI, with variation between RRT modalities and micronutrients.

Micronutrient and amino acid losses in acute renal replacement therapy.

PURPOSE OF REVIEW: A wide range of renal replacement therapies is now available to support patients with acute kidney injury. These treatments utilize diffusion, convection or a combination of these mechanisms to remove metabolic waste products from the bloodstream. It is inevitable that physiologically important substances including micronutrients will also be removed. Here we review current knowledge of the extent of micronutrient loss, how it varies between treatment modalities and its clinical significance. RECENT FINDINGS: Very few studies have specifically investigated micronutrient loss in renal replacement therapy for acute kidney injury. Recent data suggest that trace elements and amino acids are lost during intermittent dialysis, hybrid therapies such as sustained low-efficiency diafiltration and continuous therapies. Extent of micronutrient loss appears to vary with treatment type, with continuous convection-based treatments probably causing greatest losses. SUMMARY: Patients with acute kidney injury are at high risk of disease-related malnutrition. The use of renal replacement therapy, although often essential for life support, results in loss of micronutrients into the filtrate or dialysate. Losses are probably greater with continuous convective treatments, but it is not yet known whether these losses are clinically significant or whether their replacement would improve patient outcomes.