Renal Function Following Nephrectomy
Steven C. Campbell, MD, PhD
Protection of renal function is a primary concern of physicians who manage surgical or medical diseases of the kidney, such as renal tumors, urinary calculi, renal vascular disease, or ureteropelvic junction obstruction.
Although these disease entities are still managed with nephrectomy in certain situations, approaches that better preserve renal function, including partial nephrectomy, endoscopic stone surgery, angiographic management of renovascular disease, and pyeloplasty are generally preferred.
Many of these patients have pre-existing CKD or are at risk of developing CKD because they also have hypertension, diabetes, systemic atherosclerotic disease, or other comorbid conditions. Therefore preservation of renal function impacts the management of these conditions as well.
Until recently, the main focus of many urologic interventions has been to prevent or delay the need for renal replacement therapy because this end point is associated with increased mortality, as well as a substantial decline in quality of life (N Engl J Med. 2004;351:1296-1305).
Data also indicate that CKD is independently associated with morbid cardiac events and all-cause mortality in a dose-dependent fashion, even after controlling for a variety of potentially confounding factors such as hypertension and diabetes.
The finding in several population-based studies that CKD is much more common than previously recognized further emphasizes the importance of functional preservation in patients being considered for nephrectomy.
In patients with normal renal function who undergo nephrectomy, the use of serum creatinine (SCr) remains a somewhat imprecise means of determining renal function because SCr is dependent on gender, race, and muscle mass.
Estimated glomerular filtration rate (eGFR) has been shown to reflect renal function more accurately than SCr, and both the abbreviated Modified Diet in Renal Disease (MDRD) study formula and the Cockcroft-Gault equation have been used in several studies of nephrectomy patients (Lancet Oncology. 2006;7:735-740, J Am Soc Nephrol. 2005;16:459-466, J Urol. 2008;180:2363-2369).
In these studies, approximately 25%-30% of patients with “normal” SCr levels (1.4 mg/dL or less) have at least moderate CKD (GFR less than 60 mL/min/1.73m2) (Lancet Oncology. 2006, and J Urol. 2008;180:2363-2369).
Although clearly inferior to direct GFR measurement based on 125I-iothalamate renal clearance, recommendations from the National Kidney Foundation and the National Kidney Foundation Disease Education Program now call for the eGFR (based on the MDRD study formula) to be reported automatically whenever an SCr is ordered by a healthcare professional (Am J Kidney Dis. 2002;39[2 Suppl 1]:S1-S266). Because of the infeasibility of measuring GFR directly in all patients and until a better tool is developed, we believe the MDRD study formula is the best available method to estimate renal function in patients undergoing nephrectomy.
With patients living longer, it is becoming even more important to consider factors that place them at risk for CKD-associated morbidity and mortality. The renal function of all patients undergoing surgery should be optimized by appropriate IV fluid administration and the use of renoprotective agents, such as mannitol, both prior to and during surgery. Patients should also be counseled regarding the possible need for dialysis.
Although preservation of approximately 30% of the functioning nephron volume is sufficient for avoidance of renal replacement in healthy individuals, many nephrectomy patients have or are at risk for medical renal disease. This explains why the proportion of patients with CKD following radical nephrectomy exceeds 40% in recent series from centers of excellence (Lancet Oncology. 2006;7:735-740)