Evaluation of a new method for measuring vascular access recirculation.

Together with Nikkiso in Shizuoka, Japan, we developed a new method for measuring the rate of vascular access recirculation by the blood volume monitor. This measurement is performed via a method of dilution that employs a marker produced by rapid ultrafiltration using a dialysis machine. In this paper, we evaluate the reliability and safety of this machine, in vitro and in vivo. The safety of this method was evaluated by investigating hemolysis after rapid ultrafiltration. The measurement of free hemoglobin, potassium and haptoglobin in the circulating blood were performed before and after rapid ultrafiltration. No data was found to indicate hemolysis in vivo, detected by an increase in potassium or a decrease in haptoglobin. Evaluation of reliability in an experimental system was also performed on an in vitro recirculation system at a rate of 0, 10, 25, 50, and 70%. Almost all of the measured rates were within ± 10% of the theoretical rate. We performed 20 hemodialysis experiments with vascular access recirculation applying this monitor and simultaneous urea and creatinine dilution methods, which were the recommended standard measurements for vascular recirculation. In 53 measurements of standard vascular shunts with no postural change, differences of the results between the monitor and both dilution methods were only 4.0% and 3.2%, respectively. Regression analysis showed a significant and positive correlation between them (P < 0.0001). We conclude that this new method for measuring vascular access recirculation is applicable in terms of both accuracy and ease of operation.

Merits and limitations of continuous blood volume monitoring during haemodialysis. Summary of the EDTNA/ERCA Journal Club discussion: Winter 2005.

The discussion explored and expanded on the issues raised by Dasselaar et al in their review of the measurement of relative blood volume (RBV) changes during dialysis (NDT 2005). Dialysis machines incorporating blood volume monitoring and control are widely available in Europe. The use of continuous blood volume monitoring (CBVM) to help establish dry weight; problems with CBVM due to connection and use of single needle dialysis; the physiological processes that cause RBV changes during eating, exercise and posture changes; and the application of blood volume based biofeedback control were discussed by participants from ten countries. The 'take-home' messages from the discussion were that CBVM can assist in setting target weight, but must be used together with traditional measures and experience. Biofeedback control may help to achieve symptom-free dialysis, but staff should be prepared to monitor patients systematically for several weeks to obtain individualised settings. Users of CBVM should be aware of factors that can alter the central haematocrit leading to apparent changes in RBV. Practical guidelines should be developed to help staff interpret CBVM data effectively.