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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.

A B S T R A C T This study tests the hypothesis that obligatory cation coverage of metabolically generated anions is the mechanism for the sodium diuresis of fasting. Nine obese female subjects were equilibrated on a constant sodium and caloric intake and then fasted while sodium intake was maintained. Particular attention was paid to maintaining the same upright activity schedule during fasting as during control. Consecutive 3-h increases in urinary sodium, ammonium, and potassium excretion during fasting were matched against simultaneously determined increases in organic acid anions (OAS) and H2PO4-, which would exist in combination with the cations. The changes were significantly correlated (r = 0.891, P < 0.001) in the relationship y = 0.73x + 19 where y equals increases in organic acid salts + H2PO4-and x equals increases in cations. As ammonium excretion rose, sodium conservation occurred with ammonium replacing sodium at the major urinary cation. Corollaries to the hypothesis were also found to be true. They were: (a) Increases in ammonium excretion lagged considerably behind increases in OAS + H2PO4c during the diuretic phase making sodium coverage necessary. (b) Sodium loss was much greater than chloride although chloride balance was minimally negative. (c) After refeeding with glucose, sodium excretion promptly decreased and appeared best correlated with simultaneous decreases in OAS. Ammonium excretion also fell but much less than sodium. The data support the hypothesis that obligatory cation coverage of metabolically generated anions is a major mechanism responsible for the sodium diuresis of fasting. INTRODUCTIONLarge quantities of electrolyte and water are lost in the urine during the 1st wk of fasting. The principal

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