**3.5 Solute removal index (SRI) and fractional solute removal (FSR)**

An alternative for KT/V is fractional solute removal (FSR), which was suggested by Verrina et al. (Verrina et al., 1998) and Henderson (Henderson, 1999) for comparative studies of different dialysis modalities and schedules. The concept of FSR is closely related to the concept of the solute removal index (SRI) proposed by Keshaviah (Keshaviah, 1995).

SRI was defined for HD as the ratio of net solute removed during a dialysis session (i.e., the solute amount removed minus the solute amount generated in the same time period) over the initial solute amount in the body. This parameter is however useless for comparative analysis of different dialysis modalities and schedules. Its numerical value for the kidneys and continuous therapies, such as continuous ambulatory peritoneal dialysis (CAPD), is by definition equal to zero (Waniewski & Lindholm, 2004). Therefore, Keshaviah (Keshaviah, 1995) used for CAPD and automated peritoneal dialysis the definition of SRI as the ratio of solute removed during a dialysis session over its initial amount in the body, i.e., the definition of FSR.

### **3.6 International guidelines on HD dose**

According to the Kidney Disease Outcomes Quality Initiative (KDOQI) guidelines the minimally adequate dose of thrice-weekly HD in patients with residual renal clearance (Kr) less than 2 mL/min/1.73 m2 should be urea single pool KT/V (excluding residual renal function) of 1.2 per dialysis (i.e., an average urea reduction ratio of 65%), (Work Group, 2001). KDOQI Work Group emphasizes that the literature clearly supports the delivery of a minimum hemodialysis dose of at least urea spKt/V = 1.2, but does not suggest an optimal dose. Identification of an optimal dose of hemodialysis would require evaluation of patient status and clinical outcomes including survival analyses and assessment of quality of life as well as the cost-effectiveness of different hemodialysis regimens. Until such data are available, the Work Group states that the hemodialysis dose recommended is to be regarded as a minimum value only (Work Group, 2001; Work Group, 2006).

The European Best Practice Guidelines recommend higher values: the minimum prescribed HD dose per session for thrice-weekly schedule as equilibrated KT/V for urea is set at 1.2; this corresponds to a value of spKT/V equal to 1.4 (Work Group, 2002).
