THE EFFECT OF NEEDLE GAUGE ON RECIRCULATI ON AND DIALYSIS ADEQUACY

Dialysis adequacy depends on the blood flow rate through the dialyser among other factors. High performance dialysis requires high blood flo w rate and wide-bore needles are recommended. We studied the influence of two different needles (14 and 15 G) on hemodynamic parameters that may affect dialysis adequacy at requested blood flow rates between 20 0-400 ml/min. Venous pressure, arterial line pressure fall, actual blo od flow rate and urea recirculation (stop flow method and three sample method) were measured. We studied 20 patients with radiocephalic well functioning fistulae, which had been in use for 70.3 +/- 55.8 months. Venous pressure and the drop in pressure along the arterial line incr ease with increasing blood flow rate. This increase was smaller with 1 4 G needles than with 15 G ones. The increase follows a linear progres sion defined by the equations: Y = 22.15X + 38.43 and Y = 16.38X + 26. 88 for 14 G and 15 G needles respectively. For arterial line pressure fall: Y = -27.8X -18.3; and Y = -19.7X -9.3 with 14 y 15 G needles res pectively (R = 0.99 in all cases). Actual blood flow rate entering the dialyser is always smaller than the requested flow and smaller with 1 5 G needles. Ar a requested blood flow rate of 400 ml/min the actual b lood flow rate was 10.5% less with 15 G needles and 7.1% with 14 G one s. Recirculation rate by the three sample method increases with increa sing blood flow rate and is independent of needle gauge. With stop-flo w method no significant increase in recirculation rates was found with progressively greater blood flow rates. Significant differences in re circulation rate were obtained between the two methods used, with the same blood flow rate and needle gauge. Dialysis adequacy was similar a t 400 ml/min with the two needles: KT/V - 1.21 vs 1.24 with 15 and 14 respectively (NS). In conclusion, the use of 14 G rather than 15 G nee dles with well functioning radiocephalic fistula does not improve dial ysis adequacy at a blood flow rate of 400 ml/min, because neither actu al blood flow rate nor recirculation rate are changed. We could not es tablish a threshold blood flow rate for significant recirculation meas ured by the stop-flow method.