Effects of Fluid Bolus Therapy on Renal Perfusion, Oxygenation, and Function in Early Experimental Septic Kidney Injury.

Objectives: To examine the effects of fluid bolus therapy on systemic hemodynamics, renal blood flow, intrarenal perfusion and oxygenation, PO2, renal function, and fluid balance in experimental early septic acute kidney injury. Design: Interventional study. Setting: Research institute. Subjects: Adult Merino ewes. Interventions: Implantation of flow probes on the pulmonary and renal arteries and laser Doppler oxygen-sensing probes in the renal cortex, medulla, and within a bladder catheter in sheep. Infusion of Escherichia coli to induce septic acute kidney injury (n = 8). After 24, 25, and 26 hours of sepsis, fluid bolus therapy (500 mL of Hartmann's solution over 15 min) was administered. Measurements and Main Results: In conscious sheep, infusion of Escherichia coli decreased creatinine clearance and increased plasma creatinine, renal blood flow (+46% +/- 6%) and cortical perfusion (+25% +/- 4%), but medullary perfusion (-48% +/- 5%), medullary PO2 (-56% +/- 4%), and urinary PO2 (-54% +/- 3%) decreased (p < 0.01). The first fluid bolus therapy increased blood pressure (+6% +/- 1%), central venous pressure (+245% +/- 65%), cardiac output (+11% +/- 2%), medullary PO2 (+280% +/- 90%), urinary PO2 (+164% +/- 80%), and creatinine clearance (+120% +/- 65%) at 30 minutes. The following two boluses had no beneficial effects on creatinine clearance. The improvement in medullary oxygenation dissipated following the third fluid bolus therapy. Study animals retained 69% of the total volume and 80% of sodium infused. Throughout the study, urinary PO2 correlated significantly with medullary PO2. Conclusions: In early experimental septic acute kidney injury, fluid bolus therapy transiently improved renal function and medullary PO2, as also reflected by increased urinary PO2. These initial effects of fluid bolus therapy dissipated within 4 hours, despite two additional fluid boluses, and resulted in significant volume retention.