Relationship Between Residual Renal Output and Dialysis Independence in CKD Patients
Higher urine output and preserved residual kidney function strongly correlate with improved survival and potential dialysis independence in CKD patients. 1
Importance of Residual Kidney Function (RKF)
Residual kidney function plays a crucial role in the management of patients with advanced CKD, particularly those on dialysis:
- RKF represents the function of native kidneys or kidney allografts, measured by the average of 24-hour creatinine and urea nitrogen clearance 1
- Preserved RKF is associated with improved survival in both hemodialysis (HD) and peritoneal dialysis (PD) patients 1
- The association between preserved RKF and survival is robust in studies from around the world 1
Clinical Significance of Urine Output
Urine output serves as an important clinical marker in CKD patients:
- Patients with urine output exceeding 100 mL/day are considered to have significant residual kidney function 1
- Urine output roughly correlates with RKF but should not be used as the sole determinant as it doesn't predict RKF accurately in individual patients 1
- Patients with potentially recoverable renal function represent a special group where regular measurements of RKF are especially advantageous 1
Benefits of Preserved RKF in Dialysis Patients
Maintaining residual kidney function provides multiple benefits:
- Continuous clearance: RKF provides continuous clearance between dialysis treatments, which is more efficient than intermittent clearance 1
- Reduced dialysis requirements: Patients with significant RKF may require less intensive dialysis regimens 1
- Improved quality of life: Reduced need for dietary potassium and fluid restriction 1
- Decreased hospitalization: Lower frequency of hospitalizations related to fluid overload 1
Relationship to Dialysis Independence
The relationship between urine output and dialysis independence is significant:
- Failure to follow RKF closely may lead to unnecessary prolongation or perpetuation of dialysis in patients with adequate native kidney function 1
- After initiating hemodialysis, some patients experience increased urine output and improved endogenous renal function, potentially allowing discontinuation of dialysis 1
- The continuous nature of RKF contrasts with the intermittent schedule of dialysis, making RKF more efficient per unit of clearance 1
Preserving Residual Kidney Function
Several strategies can help preserve RKF in CKD patients:
- Use of ACE inhibitors or ARBs when antihypertensive medication is needed 1
- Consider ACE inhibitors or ARBs even in normotensive patients for kidney protection 1
- Avoid nephrotoxic agents that can damage remaining kidney function 1
- Use biocompatible dialysis membranes and ultrapure water for dialysis 1
Monitoring Recommendations
Regular monitoring of RKF is essential:
- Measure residual kidney urea clearance (Kr) using timed urine collections 1
- Include Kr in models of urea kinetics to allow accurate measurement of protein catabolic rate 1
- Monitor RKF monthly alongside delivered dialysis dose 1
- Consider direct measurement of GFR in selected cases where clinical symptoms appear discordant with estimated kidney function 1
Clinical Pitfalls to Avoid
Important considerations to prevent errors in management:
- Do not rely solely on estimated GFR when determining the timing of dialysis initiation or discontinuation 1, 2
- Avoid using urine volume as the only measure of residual kidney function 1
- Don't overlook the possibility of recovering kidney function in patients already on dialysis 1
- Recognize that serum creatinine-based equations may overestimate GFR in patients with low muscle mass 1
Conclusion
The evidence strongly supports that higher residual urine output and preserved kidney function correlate with better outcomes and potential dialysis independence in CKD patients. Regular monitoring of residual kidney function and implementing strategies to preserve it should be prioritized in the management of CKD patients on dialysis.