Validation of the inverse method for the determination of the access flow with thermodilution

Thermodiluction is a widely used method for measuring vascular access flow (Q_A). Among the possibilities of TD, the reverse method (MI) can be beneficial in the execution time, without impact on the dialysis efficacy (Kt). However, it is not a sufficiently studied technique.

Transversal study of 117 arteriovenous fistulas (AVF). Two Q_A measurements were taken with the method described by the manufacturer (MR) and another with MI. MI is bases in the obtention of an inverted recirculation registry at the beginning of the session and a single subsequent recirculation measurement with the lines in normal position. In the concordance analysis, the Bland-Altman method and Cohen's Kappa index were used.

Very good concordance between MR and MI was evidenced for QA below 700 ml/min, but it worsens as flow increases. The median variability between the MR measurements (intra-method variability) was 3.4% (-17.13). This value did not differ from the median variability generated between MR and MI (inter-method variability), which was 2% (-14, 12) (P = 0.287). The degree of agreement between the two to identify AVFs susceptible to intervention was very good (K = 0.834). The time spent using the MI was significantly shorter (P = 0.000) without evidence of variations in the Kt of the measurement sessions (P = 0.201).

The thermodiluction MI is valid to determine the flow of the vascular access, especially in Qa lower than 700 ml/min, with great time savings, simplification of the procedure and without modifying the dialysis efficiency. The variability between the measurement by MR and MI is similar to that of MR. The concordance between methods in identifying potentially pathological AVFs is very good.