Is it time to revisit residual renal function in haemodialysis? (Review Article)

High-sensitivity C-reactive protein, apolipoproteins, and residual diuresis in chronic kidney disease patients undergoing hemodialysis

BACKGROUND

Residual diuresis (RD) is the simplest method for measuring renal residual function in patients with chronic kidney disease (CKD). A reduction in RD is associated with intensification of the inflammatory process caused by uremia. However, little is known regarding the relation between RD and inflammatory markers in these patients. We verify possible associations among the hs-CRP, atherogenic factors, and RD, in patients with CKD undergoing hemodialysis.

METHODS

This study enrolled 80 patients with CKD undergoing hemodialysis. Patients were stratified according to RD in anuric (RD-) group (n = 47) and non-anuric (RD+) group (n = 33). Urine volumes were collected in a 24 h period during the interdialytic period. Serum high-sensitivity C-reactive protein (hs-CRP), and apolipoprotein (Apo) A1 and B levels were measured after fasting for 12 h.

RESULTS

Serum hs-CRP levels were higher in the RD- group than in the RD+ group (P = 0.015). In the total group, hs-CRP was significantly correlated with RD (r = - 0.25, P = 0.025) and Apo AI (r = - 0.25, P = 0.024). A greater proportion of patients had reduced plasma concentrations of Apo AI in the RD- group (31.9 %) compared with the RD+ group (9.1 %) (P = 0.014).

CONCLUSION

This study shows a relationship between RD and the hs-CRP in patients undergoing hemodialysis. Although the inflammatory state was verified in a large part of the CKD population, patients without RD had more elevated hs-CRP serum levels than those with RD.

Diffusion-weighted imaging of the kidneys and its relationship with residual renal function in continuous ambulatory peritoneal dialysis patients

OBJECTIVE

The objective of our study was to prospectively evaluate renal diffusion as shown by diffusion-weighted imaging (DWI) and its relationship with the residual renal function (RRF) in continuous ambulatory peritoneal dialysis (CAPD) patients.

SUBJECTS AND METHODS

Forty CAPD patients and 40 healthy volunteers were recruited, and all underwent conventional and fat-saturated echo-planar DWI with three b values (0, 300, 600 s/mm(2)). The renal parenchymal thickness and apparent diffusion coefficients (ADCs) were measured, and both were compared between the two groups. The relationships between ADC values and clinical indexes--which included RRF, serum creatinine value, cystatin C value, and urine output--were analyzed.

RESULTS

Compared with the renal parenchymal thickness and ADC values in control subjects, these values in CAPD patients were significantly decreased (p < 0.0001). In CAPD patients, the ADC values were positively correlated with RRF (r = 0.447, p = 0.004). A mild linear correlation was also found between the ADC values and cystatin C value (r = -0.352, p = 0.026).

CONCLUSION

The renal diffusion function as shown by DWI is impaired in CAPD patients and correlates with RRF.

Equivalent continuous clearances EKR and stdK in incremental haemodialysis

BACKGROUND

Many haemodialysis patients have residual renal function (RRF), which as such is insufficient to maintain satisfactory quality of life but reduces the demands of treatment and improves outcomes. In incremental dialysis, the dose is adjusted according to RRF, but how should it be done?

METHODS

Urea generation rate (G) and distribution volume (V) were determined by the double-pool urea kinetic model in 225 haemodialysis sessions of 30 patients. The effect of different degrees of RRF on equivalent renal urea clearance (EKR), standard urea clearance (stdK) and urea concentrations and required treatment times to achieve the HEMO study standard dose equivalent EKR and stdK targets were studied by computer simulations.

RESULTS

Ignoring RRF leads to underestimation of EKR, stdK, urea generation rate and protein equivalent of nitrogen appearance. Both EKR and stdK increase linearly with renal urea clearance (Kr). The HEMO standard dose equivalent EKRc is 13.8 mL/min/40 L and stdK/V 2.29 /wk (9.1 mL/min/40 L). The required treatment time to achieve the HEMO-equivalent targets has an almost linear inverse relationship to Kr. If the HEMO standard dose equivalent EKR or stdK is used as the target, RRF may replace several hours of weekly dialysis treatment time. stdK appreciates RRF more than EKR.

CONCLUSIONS

RRF is included in the original EKR and stdK concepts. EKR and stdK--determined by kinetic modelling--are promising measures of adequacy in incremental dialysis.

Contribution of residual function to removal of protein-bound solutes in hemodialysis

BACKGROUND AND OBJECTIVES

This study evaluated the contribution of residual function to the removal of solutes for which protein binding limits clearance by hemdialysis.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Solute concentrations were measured in 25 hemodialysis patients with residual urea clearances ranging from 0.1 to 6.2 ml/min per 1.73 m2. Mathematical modeling assessed the effect of residual function on time-averaged solute concentrations.

RESULTS

Dialytic clearances of the protein-bound solutes p-cresol sulfate, indoxyl sulfate, and hippurate were reduced in proportion to the avidity of binding and averaged 8±2, 10±3, and 44±13% of the dialytic urea clearance. For each bound solute, the residual clearance was larger in relation to the residual urea clearance. Residual kidney function therefore removed a larger portion of each of the bound solutes than of urea. Increasing residual function was associated with lower plasma levels of p-cresol sulfate and hippurate but not indoxyl sulfate. Wide variation in solute generation tended to obscure the dependence of plasma solute levels on residual function. Mathematical modeling that corrected for this variation indicated that increasing residual function will reduce the plasma level of each of the bound solutes more than the plasma level of urea.

CONCLUSIONS

In comparison to urea, solutes than bind to plasma proteins can be more effectively cleared by residual function than by hemodialysis. Levels of such solutes will be lower in patients with residual function than in patients without residual function even if the dialysis dose is reduced based on measurement of residual urea clearance in accord with current guidelines.