Figure 611

Monitoring the delivered dose in hemodialysis. Use of the urea reduction ratio (URR) is the simplest way to monitor the delivered dose of hemodialysis. However, a shortcoming of this method compared with formal urea kinetic modeling is that the URR does not account for the contribution of ultrafiltration to the final delivered dose of dialysis. During ultrafiltration, convective transfer of urea from blood to dialysate occurs without a decrease in urea concentration. As a result, with increasing ultrafiltration volumes the Kt/V, as determined by formal urea kinetic modeling, progressively increases at any given URR. For example, a URR of 65% may correspond to a Kt/V as low as 1.1 in the absence of ultrafiltration or as high as 1.35 when ultrafiltration of 10% of body weight occurs.

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