In vivo validation of glucose pump test for measurement of hemodialysis access flow

Background: The glucose pump test (GPT) is a recently introduced method of measuring hemodialysis access blood flow (Qa). A validation of GPT during dialysis has not yet been done, and performance characteristics of the method have not yet been fully analyzed. Methods: The authors studied 33 patients (25 synthetic grafts, 8 autogenous arteriovenous fistulae). Qa measurements by ultrasound dilution (UD) and GPT were done in triplicate during dialysis. In GPT, a baseline blood sample (C₁) was obtained, followed by infusion of a 10% glucose solution (C_i) through the arterial needle into the access at 16 mL/min (Q_i). After 11 seconds, a downstream blood sample (C₂) was aspirated from the venous needle. C₁ and C₂ glucose were measured by glucometer. Qa was computed by the equation: Qa = Q_i(C₁ - C₂)/(C₂ - C₁). A model of the access vascular circuit was used to determine the influence of C₂ aspiration on the Qa measurement. Results: Mean Qa was 1413 mL/min by UD versus 1,496 mL/min by GPT (P = 0.11). There was a strong linear correlation between the 2 methods (r = 0.905; P <0.001). The pooled coefficient of variation was 6.4% for UD and 9.6% for GPT. The circuit model showed that aspiration of C₂ causes an increase in Qa (ΔQa) that depends on the aspiration rate (Q_ASP) and fraction of resistance in the circuit that is downstream to the venous needle: ΔQa = Q_ASP(Downstream resistance)/(Total resistance). The model predicts the overestimate is approximately 62 mL/min for grafts and 120 mL/min for fistulae but may vary depending on the balance of resistances upstream and downstream to the venous needle. Conclusion: This study shows that GPT closely correlates with UD, and the method has adequate precision. GPT is an inexpensive method that may help make Qa measurements more widely available than previously possible.