Urinary Oxygenation as a Surrogate Measure of Medullary Oxygenation During Angiotensin II Therapy in Septic Acute Kidney Injury

Objectives: Angiotensin II is an emerging therapy for septic acute kidney injury, but it is unknown if its vasoconstrictor action induces renal hypoxia. We therefore examined the effects of angiotensin II on intrarenal PO2 in ovine sepsis. We also assessed the validity of urinary PO2 as a surrogate measure of medullary PO2. Design: Interventional study. Setting: Research Institute. Subjects: Sixteen adult Merino ewes (n = 8/group). Interventions: Sheep were instrumented with fiber-optic probes in the renal cortex, medulla, and within a bladder catheter to measure PO2. Conscious sheep were infused with Escherichia coli for 32 hours. At 24–30 hours, angiotensin II (0.5–33.0 ng/kg/min) or saline vehicle was infused. Measurements and Main Results: Septic acute kidney injury was characterized by hypotension and a 60% ± 6% decrease in creatinine clearance. During sepsis, medullary PO2 decreased from 36 ± 1 to 30 ± 3 mm Hg after 1 hour and to 20 ± 2 mm Hg after 24 hours; at these times, urinary PO2 was 42 ± 2, 34 ± 2, and 23 ± 2 mm Hg. Increases in urinary neutrophil gelatinase-associated lipocalin (12% ± 3%) and serum creatinine (60% ± 23%) were only detected at 8 and 24 hours, respectively. IV infusion of angiotensin II, at 24 hours of sepsis, restored arterial pressure and improved creatinine clearance, while not exacerbating medullary or urinary hypoxia. Conclusions: In septic acute kidney injury, renal medullary and urinary hypoxia developed several hours before increases in currently used biomarkers. Angiotensin II transiently improved renal function without worsening medullary hypoxia. In septic acute kidney injury, angiotensin II appears to be a safe, effective therapy, and urinary PO2 may be used to detect medullary hypoxia. Supported, in part, by grants from the National Health and Medical Research Council of Australia (1050672) and by funding from the Victorian Government Operational Infrastructure Support Grant and the Jack Brockhoff Foundation (ID 4178). Dr. Lankadeva’s institution received funding from a Jack Brockhoff Foundation Early Career Medical Research Grant and was supported by Postdoctoral Fellowship from the National Heart Foundation of Australia (NHF, 100869). Dr. Evans’ institution received funding from National Health and Medical Research Council of Australia. Dr. May’s institution received funding from National Health and Medical Research Council of Australia, National Heart Foundation of Australia, and the Jack Brockhoff Foundation, and he received other support from a Victorian Government Operational Infrastructure Support Grant. The remaining authors have disclosed that they do not have any potential conflicts of interest. For information regarding this article, E-mail: clive.may@florey.edu.au Copyright © by 2017 by the Society of Critical Care Medicine and Wolters Kluwer Health, Inc. All Rights Reserved.

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