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MICRONUTRIENT LOSS IN RENAL REPLACEMENT THERAPY FOR ACUTE KIDNEY INJURY
Weng C Oh 1,4, Mark Rigby 1, Bruno Mafrici 1, Andrew Sharman 4, Daniel Harvey 4, Simon Welham3, Ravi Mahajan4, David Gardner 2, Mark A J Devonald 1Renal and Transplant Unit, Nottingham University Hospitals NHS Trust1, School of Veterinary Medicine and Science2 and School of Biosciences3, Academic Anaesthesia, School of Medicine, University of Nottingham 4
INTRODUCTION: The prevalence of malnutrition in acute kidney injury (AKI) is high. Patients with AKI may require renal replacement therapy (RRT), which could result in loss of water-soluble micronutrients. Little is known about micronutrient losses in RRT and whether they differ between types of RRT. The aim of this study is to quantify losses of micronutrients (trace elements and amino acids) during RRT in patients with AKI and to compare losses in three different RRT modalities: continuous veno-venous haemofiltration (CVVH), intermittent haemodialysis (IHD) and sustained low-efficiency diafiltration (SLED-f).
METHODS: A prospective observational study is being conducted at NUH. All adult patients with AKI requiring RRT are eligible to participate. A clinical assessment of the patient’s nutritional status is undertaken. Samples of blood and RRT effluent (dialysate or filtrate) were obtained at baseline and subsequently at mid and end-session from each participant during their first RRT treatment. Samples were processed and stored at -80°C for subsequent analysis of amino acids by high performance liquid chromatography (Biochrom 20) and trace elements by inductively coupled mass spectrometry after derivatization from physiological fluids. Total plasma concentrations of amino acids were corrected for dialysis dose using the urea reduction ratio (for IHD & SLED-f, but not CVVH). Total losses of micronutrients during RRT were calculated by multiplying mass-corrected concentrations by total volume of RRT effluent, adjusted for baseline plasma concentrations and RRT dose (determined by the solute removal index). Data were analysed by restricted maximum likelihood estimating equations (Genstat v16, VSNi Ltd, UK). Full data were available for n=13 IHD, n=10 SLED-f and n=10 CVVH patients.
RESULTS: 73.5% of patients were malnourished using the Subjective Global Assessment tool (3-point scale). The prevalence of malnutrition is similar between patients receiving SLEDfvs. IHD (70% vs. 69.2%) but was highest in patients receiving CVVH (82%). The total plasma concentration of all standard amino acids (n=20) at baseline was similar between patients receiving IHD vs. SLED-f (1812 ± 517 vs. 2675 ± 527 µmol/L, respectively) but was considerably higher in patients receiving CVVH (3194 ± 564 µmol/L). RRT reduced the plasma concentration of amino acids in patients receiving SLED-f (to 1732 ± 529 µmol/L; P=0.02), but had no effect in those receiving IHD or CVVH (IHD; 1853 ± 523, CVVH; 2845 ± 512 µmol/L). The average, unadjusted loss of amino acids was significantly influenced by mode of RRT (IHD, 5.13 ± 3.1 vs. SLED-F, 8.21 ± 4.07 vs. CVVH, 18.69 ± 3.04 gms; P<0.01). 23 trace elements were present at detectable concentrations in plasma. The total baseline plasma concentration of trace elements was similar between patients receiving IHD, SLED-f and CVVH (3797 ± 827, 3667 ± 791, 3642 ± 481 µg/L, respectively). By the end of each session of RRT, the plasma concentration of trace elements in patients had reduced (IHD, to 3103 ± 827; SLED-f, to 2805 ± 797; CVVH, to 3433 ± 481 µg/L; P=0.01). By the end of each session of RRT total losses of trace elements were estimated at IHD, 5051 ± 2312; SLED-f, 8751 ± 2421; CVVH, 11,258 ±2547 ug/L; P=0.02 for treatment.
CONCLUSION: Micronutrients are lost during RRT in AKI. The amount lost is influenced by the type of RRT modality used. Micronutrient lossesarehighest in patients receiving CVVH. The prevalence of malnutrition is high in patients in AKI stage 3.