MD GRECC (Geriatric Research, Education, and Clinical Center) Salt Lake City VA Medical Center and the University of Utah Department of Anesthesiology.
Introduction: Acute kidney injury (AKI) is a complication of hemorrhage associated with increased morbidity, mortality, and prolonged hospitalization. AKI diagnosis relies on a rise in serum creatinine, which takes 1-2 days after the initial insult, thus precluding prevention. Urine oxygen (PuO₂) correlates with renal medullary oxygen and predicts AKI. We hypothesize that PuO₂-guided resuscitation from hemorrhage better preserves renal oxygen compared to standard protocols.
Methods: After IACUC approval, oxygen sensors were placed in the renal medulla and at the tip of a urinary catheter in 16 anesthetized swine. After baseline measurements, each animal underwent staged hemorrhage (25 mL/kg). Subjects then underwent a 1h resuscitation with either a standard protocol based on mean arterial pressure, central venous pressure, and urine output or a PuO2-guided resuscitation protocol. This was followed by a 1h observation period. The primary outcome was renal medullary oxygen concentration; secondary outcomes included duration of medullary hypoxia ( < 20 mmHg), units of blood administered, and serum creatinine. Statistical analysis was performed using t-tests.
Results: Three animals were excluded from the study (one from each group died due to an air embolism during rapid infusion; one animal's renal oxygen sensor was malpositioned). Baseline, end of hemorrhage, resuscitation, and observation renal medullary oxygen were not statistically different between the standard and PuO2 groups (43 vs 52 mmHg p=0.31; 10 vs 13 p=0.68; 61 vs 51 p=0.35; 60 vs 54 p=0.43 respectively) nor was hypoxia time during resuscitation (270 vs 242 seconds p=0.90). The PuO2 group, however, was administered significantly fewer units of blood during the resuscitation (2.7 vs 1.1 units p=0.004). At the end of the experiment, there was no difference in serum creatinine (1.73 vs 1.79 mg/dL p=0.49).
Conclusions: PuO₂-guided resuscitation during hemorrhage maintained comparable medullary oxygenation and a similar duration of hypoxia as standard protocols but used significantly less blood. PuO₂ may serve as a valuable resuscitative endpoint, particularly in austere settings where blood transfusion is constrained by transport and storage limitations. Further clinical studies are needed to assess the applicability of these findings to humans.
