<p>Acute kidney injury (AKI), particularly during cardiac surgery, severely affects patient outcomes, yet current diagnostics using serum creatinine levels delay detection. This study investigates real-time urinary oxygen tension (PuO₂) as an alternative early marker and correlates it with renal medullary oxygen tension for potential AKI prediction. We developed a modified 3-way silicone urinary catheter designed for more reliable urine collection and evaluated its performance in terms of PuO₂ measurement accuracy. The results of the experiment showed that the improved catheter enabled continuous urine collection, but it was suggested that the oxygen permeability of the silicone material may have caused an increase in PuO₂ level. These results suggest that material selection, particularly oxygen permeability, has a significant impact on PuO₂ measurements and highlight the need for alternative low-permeability materials to improve the reliability of PuO₂-based AKI diagnostics.</p>