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.