Use of the Fractional Excretion of Urea in an Azotemic Nonoliguric State: Type 1 Cardiorenal Syndrome

The fractional excretion of urea is a useful tool to evaluate renal function in oliguric states; however, it remains unexplored in nonoliguric states. We evaluated its use to predict responses in patients with type 1 cardiorenal syndrome. This was a prospective observational study of 116 patients with type 1 cardiorenal syndrome referred over a 4-year period. Fractional excretion of urea and sodium, ejection fraction, mean arterial pressure, age, sex, diabetes, brain natriuretic peptide (BNP), serum sodium and blood urea nitrogen were analyzed for effects upon serum creatinine and survival. Improvement of renal function correlated most significantly with FeUrea (P = 0.00001) followed by the FeNa (P = 0.005) but no other variable studied reached significance. Survival was best predicted by improvement of the serum creatinine at 24 h (P = 0.005) and 7 days after all inotropes were stopped (P = 0.001). A limitation of this study is that it cannot be extrapolated to all cardiorenal syndrome patients other than type 1. Also, the study was not randomized and those with potentially worse disease have had worse outcomes due merely to worse underlying disease. The success of the FeUrea may possibly be related to interference of dobutamine on creatinine levels. Despite being a nonoliguric state, the FeUrea appears to provide insight to those patients with type 1 cardiorenal syndrome whose renal function (as measured by serum creatinine) and survival might improve.