Renal microvascular oxygen tension during hyperoxia and acute hemodilution assessed by phosphorescence quenching and excitation with blue and red light.

PURPOSE

The kidney plays a central physiologic role as an oxygen sensor. Nevertheless, the direct mechanism by which this occurs is incompletely understood. We measured renal microvascular partial pressure of oxygen (PO) to determine the impact of clinically relevant conditions that acutely change PO including hyperoxia and hemodilution.

METHODS

We utilized two-wavelength excitation (red and blue spectrum) of the intravascular phosphorescent oxygen sensitive probe Oxyphor PdG4 to measure renal tissue PO in anesthetized rats (2% isoflurane, n = 6) under two conditions of altered arterial blood oxygen content (CO): 1) hyperoxia (fractional inspired oxygen 21%, 30%, and 50%) and 2) acute hemodilutional anemia (baseline, 25% and 50% acute hemodilution). The mean arterial blood pressure (MAP), rectal temperature, arterial blood gases (ABGs), and chemistry (radiometer) were measured under each condition. Blue and red light enabled measurement of PO in the superficial renal cortex and deeper cortical and medullary tissue, respectively.

RESULTS

PO was higher in the superficial renal cortex (~ 60 mmHg, blue light) relative to the deeper renal cortex and outer medulla (~ 45 mmHg, red light). Hyperoxia resulted in a proportional increase in PO values while hemodilution decreased microvascular PO in a linear manner in both superficial and deeper regions of the kidney. In both cases (blue and red light), PO correlated with CO but not with MAP.

CONCLUSION

The observed linear relationship between CO and PO shows the biological function of the kidney as a quantitative sensor of anemic hypoxia and hyperoxia. A better understanding of the impact of changes in PO may inform clinical practices to improve renal oxygen delivery and prevent acute kidney injury.