Amino acid losses during sustained low efficiency dialysis in critically ill patients with acute kidney injury.

OBJECTIVE: Sustained low efficiency dialysis (SLED) involves the use of standard dialysis machines for prolonged intermittent renal replacement therapy in critically ill patients. In this study we aimed to quantify dialysate amino acid (AA) and albumin losses in 5 patients who underwent successful SLED treatment. DESIGN: This was a prospective observational study. SETTING: The study was performed in a general intensive care unit. SUBJECTS: The study was performed in critically ill patients with acute kidney injury undergoing SLED using low-flux hemodialyzers. INTERVENTION: We performed total dialysate collection and measured dialysate AA profiles by reverse phase high-pressure liquid chromatography using an automated AA analyser. MAIN OUTCOME MEASURE: Individual and total amino acid losses. RESULTS: Albumin was undetectable in dialysate. The median (mean ± SD) total amino acid loss was 15.7 (23.4 ± 19.2) g/treatment, or 122.1 (180.6 ± 148.5) mmol/treatment. Two patients were receiving intravenous nutrition. One patient had severe hepatic failure with encephalopathy, and had high dialysate AA levels with a total loss of 57 g/treatment. CONCLUSIONS: During SLED with low-flux hemodialyzers, albumin losses are negligible but AA losses to dialysate are comparable to those during continuous renal replacement therapy. Patients' nutritional protein prescriptions should be augmented to account for this.

Urea kinetics during sustained low-efficiency dialysis in critically ill patients requiring renal replacement therapy.

Continuous renal replacement therapies have practical and theoretical advantages compared with conventional intermittent hemodialysis in hemodynamically unstable or severely catabolic patients with acute renal failure (ARF). Sustained low-efficiency dialysis (SLED) is a hybrid modality introduced July 1998 at the University of Arkansas for Medical Sciences that involves the application of a conventional hemodialysis machine with reduced dialysate and blood flow rates for 12-hour nocturnal treatments. Nine critically ill patients with ARF were studied during a single SLED treatment to determine delivered dialysis dose and the most appropriate model for the description of urea kinetics during treatment. Five patients were men, mean Acute Physiology and Chronic Health Evaluation (APACHE) II score was 28.9 and mean weight was 92.5 kg. Kt/V was determined by the reference method of direct dialysate quantification (DDQ) combined with an equilibrated postdialysis plasma water urea nitrogen (PUN) concentration and four other methods that were either blood or dialysate based, single or double pool, or model independent (whole-body kinetic method). Solute removal indices (SRIs) were determined from net urea removal and urea distribution volume supplied from DDQ (reference method) and by mass balance using variables supplied from blood-based formal variable-volume single-pool (VVSP) urea kinetic modeling. Equivalent renal urea clearances (EKRs) were calculated from urea generation rates and time-averaged concentrations for PUN based on weekly mass balance with kinetic variables supplied by either DDQ (reference method) or formal blood-based VVSP modeling. Mean Kt/V determined by the reference method was 1.40 and not significantly different when determined by formal VVSP modeling, DDQ using an immediate postdialysis PUN, or the whole-body kinetic method. Correction of single-pool Kt/V by a Daugirdas rate equation did not yield plausible results. Mean SRI and EKR by the reference methods were 0.61 and 24.8 mL/min, respectively, and not significantly different when determined by blood-based methods. A single-pool urea kinetic model adequately described intradialytic PUN profiles, indicating that SLED was associated with minimal urea disequilibrium. This was supported by the parity between hemodialyzer and whole-body urea clearances, and the mean postdialytic urea rebound of 4.1% (P = 0.13 versus zero). Additional prospective studies are needed in this setting to define the optimal method for dialysis quantification, targets for azotemic control, and optimal modality of renal replacement therapy. In conclusion, SLED delivers a high dose of dialysis with minimal associated urea disequilibrium and can be quantified by Kt/V, SRI, and EKR from blood-based methods using single-pool urea kinetic models.