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, Po ₂ , 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 Po ₂ (-56% ± 4%), and urinary Po ₂ (-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 Po ₂ (+280% ± 90%), urinary Po ₂ (+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 Po ₂ correlated significantly with medullary Po ₂ . Conclusions: In early experimental septic acute kidney injury, fluid bolus therapy transiently improved renal function and medullary Po ₂ , as also reflected by increased urinary Po _2. These initial effects of fluid bolus therapy dissipated within 4 hours, despite two additional fluid boluses, and resulted in significant volume retention.