Fractional excretion of sodium predicts worsening renal function in acute decompensated heart failure

Renal impairment (RI), defined as an increase in creatinine level of greater than 26.5 mmol/L, develops in more than 30% of acute decompensated heart failure (ADHF) patients. Fractional excretion of sodium (FeNa) reflects sodium handling by the kidneys during diuresis.

To study the relationship between FeNa and RI in patients admitted with ADHF.

The hospital course and renal function of all ADHF patients admitted to the hospital were prospectively observed. Patients were included if their admission creatinine level was 176 mmol/L or lower, they had been on a low-salt diet since admission, had urine sodium and creatinine samples collected more than 6 h after a furosemide dose in the first few days of admission, and they were on daily intravenous furosemide doses of 20 mg or more.

Over six months, 51 patients met the inclusion criteria; the average daily dose of intravenous furosemide was 58.8 mg. RI developed in 39% of patients. A FeNa cut-off point of 0.4% was determined using ROC curve analysis; patients with a FeNa of greater than 0.4% (28 patients) were compared with patients with a lower FeNa (23 patients). Admission creatinine level and furosemide dose were higher in the first group (P=0.01 and P=0.06, respectively). The first group developed RI more frequently (OR=6.3; 95% CI 1.7 to 23.5; P=0.0047; adjusted OR for admission creatinine = 6.18; 95% CI 1.6 to 24.5; P=0.0096; and adjusted OR for furosemide dose = 4.7; 95% CI 1.3 to 16.7; P=0.016). They had a longer hospitalization course (median nine days [interquartile range 6.3 to 13.5 days] versus seven days [interquartile range 4.0 to 9.0 days]; P=0.036) and they were admitted to the cardiac care unit more frequently (OR=6.8; 95% CI 1.3 to 34.9; P=0.02).

A FeNa of greater than 0.4% more than 6 h after a dose of diuretics predicts RI and a complicated hospital course in ADHF patients.