Micronutrient Loss During Renal Replacement Therapy for Acute Kidney Injury

1994

Micronutrient loss during renal replacement therapy for acute kidney injury.

Weng C Oh 1,4, Mark Rigby 4, Bruno Mafrici 4, Andrew Sharman1, Daniel Harvey 1, Simon Welham3, RaviMahajan1, David Gardner 2, Mark A J Devonald1,4

Division of Anaesthesia, School of Clinical Sciences 1, School of Veterinary Medicine and Science2 and School of Biosciences3, University of Nottingham, Renal and Transplant Unit, Nottingham University Hospitals NHS Trust4

Introduction: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 modalities of RRT. The aim of this study is to quantify micronutrient loss (trace elements and amino acids) during RRT in patients with AKI and to compare losses in intermittent haemodialysis (IHD) and sustained low-efficiency diafiltration (SLED-F).

Methods:A prospective observational study is being conducted at NUH. Adults with AKI requiring RRT are eligible. Each participant has a clinical nutritional assessment performed by a renal dietitian. Blood and RRT effluent (dialysate or filtrate) are sampledat baseline, mid- and end-session from each participant during their first two RRT treatments. Samples are stored at -80°C until analysis of amino acids by high performance liquid chromatography (Biochrom 20) and trace elements by inductively coupled mass spectrometry after derivatisation from physiological fluids. Totalmicronutrientlossesduring dialysis arecalculated by multiplying known concentrations by total volume of RRT effluent, adjusted to plasma concentrations (baseline and end-session) and the ‘dialysis dose’ – determined by the urea reduction ratio and/or Kt/V. Data areanalysed by restricted maximum likelihood estimating equations (Genstat v16, VSNi Ltd, UK).Full data are available for n=7 IHD and n=4 SLED-F patients, of which n=4 IHD and n=2 SLED-F are diabetic.

Results:Total plasma concentrations of all standard (20) amino acids at baseline were similar between patients receiving IHD vs. SLED-F (992 ± 120 vs. 1036 ± 150 µmol/L, respectively) and did not change significantly by the end of each dialysis session (837 ± 120 vs. 844 ± 140 µmol/L, respectively) or after correction for Kt/V (IHD, 0.34 vs. SLED-F, 1.0).The unadjusted loss of amino acids was similar between dialysis types (IHD, 5.50 ± 0.94 vs. SLED-F, 4.01 ± 1.32 µmol/L), but tended to be less in patients with diabetes, regardless of the type of dialysis(control, 8.14 ± 1.25 vs. diabetic, 1.37 ± 1.44). Correction for plasma concentration and dialysis dose exacerbated the difference in total loss of amino acids between types of dialysis; nevertheless the effect remained non-significant due to variability between patients (IHD, 6.83±1.58g vs. SLED-F, 2.17±2.54g, P=0.29).

Excluding Na, Mg, Ca, K, 18 trace elements were measurable in dialysate. The rate of loss of any trace element did not appear to differ throughout the course of a IHD or SLED-F session (sampling at 15min intervals for up to 6h). Strontium, iron, and zinc were lost to dialysate in the greatest quantities (27 ug/L, 14 ug/L and 9 ug/L, respectively). There was no apparent difference in trace element losses between RRT modalities.

Conclusion:Unadjusted losses of free amino acids and 18 trace elements in acute IHD and SLED-F appear to be similar, despite theoretical concerns that the extended hybrid treatment might confer increased risk of micronutrient loss. It is not yet clear whether these losses are likely to be clinically significant and whether specific nutritional supplements should be used in acute RRT. This is the subject of further investigation, as is comparison with micronutrient losses during continuous veno-venous haemofiltration.