Background: Several biochemical urine tests and derived indices are reported as useful in the diagnosis of acute renal failure (ARF) and its classification in prerenal (hypoperfusion) or intrarenal (acute tubular) necrosis. However, they have not been adequately studied in sepsis, the most frequent cause of ARF in ICU.
Methods: In 10 female Merino ewes, we implanted flow probes around the pulmonary and renal arteries to measure cardiac output and renal blood flow (RBF) continuously. Cardiovascular variables were monitored and urine samples collected during a 48 h control period and one week later during a 48 h period of hyperdynamic sepsis induced by an infusion of live Escherichia coli.
Results: Infusion of live E. coli induced systemic hyperdynamic sepsis with renal vasodilatation and increased RBF. Serum creatinine increased from 73.3 +/- 15.1 to 276.9 +/- 156.3 micromol/l (P < 0.05) and creatinine clearance decreased from 84.6 +/- 21.4 to 27.5 +/- 21.4 ml/min (P < 0.05). Urine sodium concentration (UNa) decreased significantly from 164.5 +/- 50.4 to 14.6 +/- 14.3 mmol/l, fractional excretion of sodium (FeNa) from 1.5 +/- 0.17 to 0.12 +/- 0.11%, fractional excretion of urea nitrogen (FeUn) from 62.7 +/- 9.5 to 11.5 +/- 15.4%, and urine osmolality from 724.8 +/- 277.1 mosmol/l to 329.0 +/- 52.1 mosmol/l. The u/p creatinine ratio did not change.
Conclusion: Sustained Gram-negative sepsis induced a hyperdynamic state and hyperaemic ARF. Despite increased renal perfusion, UNa, FeNa and FeUn decreased significantly. Our findings suggest that, in sepsis, these urinary biochemical changes are not reliable markers of renal hypoperfusion.