Variable blood pump flow rates and the effect on recirculation.
There has been a movement in the dialysis community towards higher blood pump flow rates (QB) during dialysis. However, the effects of increased QB on recirculation and consequently the impact on clearances have not been well quantified for clinically relevant QBS. We studied the effect of QB on recirculation in 16 patients in a prospective fashion. Blood pump speeds of 200, 250, 300, 350, 400, 450, and 500 cc/min were studied in a randomized order. For QBS of 350 cc/min and greater, 14-gauge needles were used; at lower QBS, 16-gauge needles were used. The needles were positioned at least 5 cm apart. Recirculation studies were done after stabilization of QB during the first 15 minutes of dialysis with a dialysate temperature of 37 degrees C and minimal transmembrane pressure. Recirculation was calculated using the three-needle technique. All patients had an angiogram performed upon completion of the study. Effective clearances were calculated to demonstrate the effect of QB on Recirculation rates increased with increased QB (r = 0.43). Recirculation was 12.1% +/- 1.2 (Mean +/- SEM) at a QB of 200 cc/min versus 23.8% +/- 3.0 at a QB of 500 cc/min (p < 0.05). Venous pressures increased with increasing QBS, 120.0 mmHg +/- 7.3 at a QB of 200 cc/min to 204.2 mmHg +/- 9.1 at a QB of 500 cc/min. Bleeding from needle puncture sites only occurred with use of the 14-gauge needles (p = 0.02). Effective dialyzer urea and B12 clearances for six different dialyzers increased at a considerably lower rate beyond a QB of 300 cc/min.(ABSTRACT TRUNCATED AT 250 WORDS)