The furosemide stress test, electrolyte response and Renal Index in critically ill patients

Acute kidney injury (AKI) is a common syndrome in critically ill patients. The diagnostic ability of traditional markers such as serum creatinine has recently been questioned, and the use of newer tests such as the furosemide stress test or the ultrasound assessment of renal resistive index have been proposed. Aim of the present study was to compare the response to a furosemide stress test, the Renal Index in mechanically ventilated patients with and without acute kidney injury at admission, and who did or did not develop AKI at day three, among those with normal renal function at the CIU admission.

Prospective observational study in consecutive mechanically ventilated patients admitted in a general intensive care. Furosemide stress test and ultrasonographical Renal Index were performed at the admission and clinical and laboratory data were collected before and two hours after the furosemide stress text. The urine output after the first and the second hours was recorded.

Forty patients were enrolled, 19 of whom had AKI at admission. The Renal Index was significantly higher in patients with AKI (0.77±0.07 vs. 0.72±0.08, P=0.027); patients with AKI had a significantly lower urine output after the furosemide stress test (400 [340; 1400] vs.1525 [400; 2550] mL; P=0.013). The plasma concentrations of sodium, potassium and chloride were not different before and after the furosemide stress test in patients with and without AKI, whereas in patients with AKI, the total urine output of sodium, potassium and chloride were significantly lower compared to patients without AKI. Similar results were found in patients without AKI at admission and who developed AKI at day three as compared to those who did not develop AKI.

The response to the furosemide stress test and the Renal Index could be used as additional tools to evaluate the kidney function in critically ill patients.