VARIABLE BLOOD PUMP FLOW-RATES AND THE EFFECT ON RECIRCULATION

There has been a movement in the dialysis community towards higher blo od pump flow rates (Q(B)) during dialysis. However, the effects of inc reased Q(B) on recirculation and consequently the impact on clearances have not been Well quantified for clinically relevant Q(B)s. We studi ed the effect of Q(B) on recirculation in 16 patients in a prospective fashion. Blood pump speeds of 200, 250, 300, 350, 400, 450, and 500 c c/min were studied in a randomized order. I;or Q(B)s of 350 cc/min and greater, 14-gauge needles were used; at lower Q(B)s, 16-gauge needles were used. The needles were positioned at least 5 cm apart. Recircula tion studies were done after stabilization of Q(B) 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 demon strate the effect of Q(B) on recirculation. Recirculation rates increa sed with increased Q(B) (r = 0.43). Recirculation was 12.1% +/- 1.2 (M ean +/- SEM) at a Q(B) of 200 cc/min versus 23.8% +/- 3.0 at a Q(B) of 500 cc/min (p <0.05). Venous pressures increased with increasing Q(B) s, 120.0 mmHg +/- 7.3 at a Q(B) of 200 cc/min to 204.2 mmHg +/- 9.1 at a Q(B) of 500 cc/min. Bleeding from needle puncture sites only occurr ed with use of the 14-gauge needles (p = 0.02). Effective dialyzer ure a and B-12 clearances for six different dialyzers increased at a consi derably lower rate beyond a Q(B) of 300 cc/min. In conclusion, the use of higher Q(B)s results in higher venous pressures and recirculation rates which compromise effective clearances.