Solute transport in continuous hemodialysis: a new treatment for acute renal failure

A pumpless dialysis technique which combines continuous convection and diffusion was studied in 15 critically ill acute renal failure patients. Fluid identical in composition and purity to that used in peritoneal dialysis was continuously circulated (single-pass) at 16.6 cc/min through the dialysis compartment of a 0.43 m2 flat plate PAN membrane dialyzer. Whole blood clearances for urea, creatinine and phosphate averaged 25.3 +/- 4.4 cc/min, 24.1 +/- 5.5 cc/min and 21.3 +/- 5.6 cc/min, respectively. Over the range of blood flows studied (50 to 190 cc/min) clearances of these solutes were independent of blood flow rate but rather were determined by both dialysate flow rate and ultrafiltration rate. In contrast net fluxes of calcium and sodium were correlated only with ultrafiltration rate. Bicarbonate loss was 0.52 +/- 0.11 mEq/min; K+ balance varied with dialysate K+; glucose uptake from dialysate was 107 +/- 24.0 mg/min. In fresh non-clotting dialyzers, mean ultrafiltration rate was 8.1 cc/min. At QBi of 70 to 190 cc/min, dialysate and blood solute equilibrate yielding a total clearance equal to the dialysate outflow, or 25 cc/min, that is, the sum of dialysate flow rate plus ultrafiltration rate. In comparison to currently used continuous arteriovenous hemofiltration (CAVH), the exceptionally-high solute clearances obtained with continuous hemodialysis constitute a significant improvement in continuous renal replacement therapy.