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Clinical Benefit of Preserving Residual Renal Function in Dialysis Patients: An Update for Clinicians Source: Brener ZZ, Kotanko P, Thijssen S, et al. Clinical Benefit of Preserving Residual Renal Function in Dialysis Patients: An Update for Clinicians. Am J Med Sci. 2010;339(5):453–456. Introduction to Residual Renal Function • Residual renal function (RRF) plays a vital role in maintaining fluid balance, phosphorus control and removal of uremic toxins. • Decline in RRF is associated with anemia, inflammation and malnutrition in patients with end-stage renal disease, and exhibits a dominant predictor of mortality; especially in patients on peritoneal dialysis (PD). • Residual renal function in patients on hemodialysis (HD) is not significant, as RRF declines rapidly in patients on HD. • The present article provides the data on positive impact of RRF on the survival and quality of life of patients on dialysis, and the current strategies to preserve RRF in patients on PD and HD. Benefits of Preserved Residual Renal Function Residual Renal Function and Patient Survival • In 1995, a study confirmed that there was an independent relationship between the presence of RRF and survival in patients on dialysis. • It was showed that every 1 mL/min increase in glomerular filtration rate (GFR) was related with a 40% reduced risk of death in the complete study group and a 50% reduced risk of death in patients on PD. • The other study showed that the prognostic power for mortality in patients on PD was attributed to RRF and not to the dose of PD. • Therefore, RRF plays a major role in the survival of both patients on HD and PD and it is suggestive to preserve the RRF. Residual Renal Function: Volume Control, Cardiac Hypertrophy and Metabolic Control • Residual renal function plays a vital role in maintaining the fluid balance in patients on dialysis. Suboptimal sodium and water removal in patients on PD leads to greater rates of all-cause hospitalization and mortality. • Fluid restriction can be reduced or prevented by RRF. • There exists an inverse correlation between the left ventricular hypertrophy and RRF. • The risk factors for cardiac hypertrophy in patients on dialysis are associated with RRF. • The most commonly documented benefit of RRF includes middle molecule clearance. • Significant RRF lowers β₂-mocroglobulin levels thereby less chances of dialysis-associated amyloidosis. • Preserved RRF is associated with lower blood levels of uric acid, potassium and aluminum. Residual Renal Function and Inflammation • Patients undergoing dialysis are prone to inflammation that represents a dominant predictor of mortality. • Loss of RRF is correlated with an increased inflammatory response as denoted by elevated solute vascular cell adhesion molecules (vascular cell adhesion molecule 1) and Creactive protein levels in patients on PD. • It has also been shown that loss of RRF may be correlated with increased production of cytokines and impaired renal elimination of proinflammatory cytokines. Residual Renal Function and Nutritional Status • Residual renal function contributes significantly to the overall nutritional status by enhancing appetite, dietary protein and total caloric intake. Measurement of Residual Renal Function • The standard means of renal measurement include GFR measured by isotope clearance. • The other tests that are used to assess RRF in CKD include serum creatinine, creatinine clearance, urea clearance, an average of the creatinine and urea clearances, and urine volume. • The simplest measure of RRF is urine volume. Preservation of Residual Renal Function Impact of Dialysis Modality • Based on the data from many studies, it was shown that RRF was preserved more with PD than HD. • This may be due to better hemodynamic stability with PD that may minimize ischemic renal insults and the avoidance of extracorporeal circulation of HD that encourages systemic inflammation, oxidative stress and subsequent kidney injury. • Therefore, patients with RRF should adopt PD as their initial dialysis modality as strategy to maximize RRF preservation and thus improve the survival. Avoidance of Extracellular Fluid Volume Depletion • It has been recommended that episodes of volume depletion in patients to be an independent risk factor for the loss of RRF. • A study confirmed that strict volume control in patients on PD led to decrease in left ventricular hypertrophy and mean urine volume. • Despite normal blood pressure, the decrease in RRF may have been caused by subclinical hypovolemia as a result of overzealous extracellular fluid volume depletion. • Moreover, there were no effects of diuretics on RRF and can be used to provide better control of fluid balance. Avoidance of Nephrotoxic Insults • Residual renal function can be preserved by avoiding the use of radiocontrast agents or nephrotoxic drugs such as nonsteroidal antiinflammatory drugs or aminoglycosides. • Aminoglycoside nephrotoxicity can be avoided by opting once-daily dosing, avoidance of concomitant nephrotoxins, monitoring of drug levels and choice of the least nephrotoxic aminoglycoside. Antihypertensive Medications • Drugs that preserved RRF include angiotensinconverting enzyme inhibitors and calcium channel blockers. • This preservation was statistically significant in patients with PD or HD. • A study conducted by Li et al. confirmed that patients on PD treated with ramipril showed slower rate of RRF loss compared with the control group. Summary • Residual renal function is an advantage to patients on dialysis. • Residual renal function is associated with the clearance of both small- and medium-sized solutes. • Residual renal function plays a vital role in maintaining the cardiovascular health, nutritional status and wellbeing of patients on dialysis. • Residual renal function exhibits a positive effect on the survival of patients on PD. • Residual renal function should be preserved even after patients are started on dialysis treatment, irrespective of the modality used. Comprehensive Basket in Anemia Management