Clinical Developments

What is Acute Kidney Injury?

Acute Kidney Injury (AKI) is a sudden and rapid decline in kidney function, leading to a build-up of waste products and fluids in the body. It is characterized by a sudden decrease in urine output, an increase in serum creatinine levels, and disruptions in electrolyte balance. AKI can be caused by various factors, including dehydration, decreased blood flow to the kidneys, infections, medications, or underlying health conditions like heart failure or liver disease and is diagnosed through blood tests, urine tests, and imaging studies.

Treatment involves addressing the underlying cause, managing complications, and supporting kidney function through medications, fluid management, and sometimes dialysis.

Early recognition and prompt intervention are crucial to preventing complications and to promoting kidney recovery. Serum creatinine and oliguria (which refers to a decreased urine output) are the most commonly used markers to assess kidney function, but they may not be the most sensitive or specific predictors of Acute Kidney Injury (AKI), especially in the early stages. For example, creatinine levels may not rise immediately after kidney injury, limiting its effectiveness as a marker for detecting AKI in its early stages, when intervention is most effective.

Oliguria is also often considered a symptom or a marker associated with acute kidney injury (AKI). However, it alone is not always a reliable predictor of AKI.

Urinary Oxygen (PuO₂) Monitoring

Patients who are unwell or undergoing surgery routinely have a urinary drainage catheter fitted in order to continuously drain the bladder. Oxford Optronix have developed a unique within-catheter device (patent pending) that integrates a tiny, disposable, oxygen sensor connected to a bedside monitor. This device continuously monitors dissolved oxygen levels within the urine as it enters the catheter.

The partial pressure of oxygen in urine (PuO₂) may be a predictor of Acute Kidney Injury (AKI) because it reflects the oxygen tension within the kidney tissue. In healthy kidneys, there is a delicate balance between oxygen supply and oxygen demand. When there's a disruption in this balance and a change in the kidney's oxygenation status, this change is reflected in urine oxygenation, which may thereby indicate potential kidney injury or dysfunction.

A few reasons why PuO₂ might be a good predictor of AKI:

• Tissue oxygenation: The kidneys require adequate oxygenation to function properly. Reduced PuO₂ levels can indicate decreased oxygen supply to the kidney tissues, which might occur in conditions associated with AKI.
• Ischemia/re-perfusion injury: AKI often results from changes to blood supply, e.g., a reduction in blood flow to the kidneys, leading to ischemia (lack of oxygen). Monitoring PuO₂ can help assess the extent of ischemia and the potential for kidney damage.
• Early indicator: Changes in PuO₂ levels may precede other traditional markers of kidney injury. Therefore, it may serve as an early indicator, allowing for timely intervention to prevent or minimize AKI.
  
• Continuous and non-invasive: Compared to other methods, the PuO₂ measurement is both continuous and non-invasive (since the patient will already be fitted with a drainage catheter).
  

Scientists and clinicians continue to explore a range of biomarkers and indicators to improve the early detection and management of AKI, and PuO₂ is among the emerging factors being studied for its potential in this field.