Noninvasive transcutaneous determination of access blood flow rate

Background. Current indicator dilution techniques for determining the vascular access blood Row rate (Q(a)) require reversal of the dialysis blood lines and are time consuming. We have recently described an indicator dilution technique for determining Q(a) using a novel optical transcutaneous hematocrit (Hct) sensor that does not require reversal of the dialysis lines. and have validated the accuracy of this method (TQ(a)) in vitro. Methods. This study compared results using the TQ(a) method with those obtained using a similar indicator dilution technique but which required reversal of the dialysis lines (HD01 Monitor. Transonic Systems, Ithaca, NY. USA) during routine hemodialysis in 59 patients (25 native fistulas and 34 synthetic grafts). The sensor for the TQ(a) method was placed on the skin directly over the access to measure changes in Hct approximately 25 mm downstream of the venous needle. A single 30 mi bolus of saline was infused into the dialyzer venous line over approximately six seconds without reversal of the dialysis blood lines, and the vascular access flow rate was calculated using indicator dilution methods from the time-dependent decrease in the Hct downstream of the venous needle. Two additional small-scale studies were performed to assess the effect skin pigmentation and to evaluate further the reproducibility of the TQ(a) method. Results. Q(a) values determined by the TQ(a) method were highly correlated with those determined by the HD01 method (N = 72. R-2 = 0.948. P < 0.001) over the range of 153 to 2,042 mL/min. There was no significant difference between vascular access how rates determined hy the TQ(a) method and those determined by the HD01 method. Results from one small-scale study showed that the relationship between Q;, values determined by the TQ(a), and the HD01 methods was similar when tested only among black patients (N = 12). suggesting that skin pigmentation is not an important determinant of the accuracy of the TQ(a), method. The second small-scale study showed that the intratreatment coefficient of variation for the TQ(a), method was 7.8 +/- 5.6% (N = 14), Conclusions. These results show that transcutaneous measurement of Q(a) is an accurate, simple, and fast technique for determining Q(a) without requiring the reversal of the dialysis blood lines.