Hemodialysis (HD) is the main renal replacement therapy for patients with end-stage renal disease (ESRD), accounting for approximately 69% of all renal replacement therapies and 89% of all dialysis. However, factors such as unstable hemodynamics have led to the gradual loss of residual renal function (RRF) in HD patients, which not only affects the adequacy of dialysis and complications control but also impacts their quality of life and survival. Unfortunately, until now, there have been no effective methods for early diagnosis and prediction of residual renal injury, and by the time it was discovered, the opportunity for effective treatment had been missed. The purpose of this study is to validate the value of near-infrared spectroscopy (NIRS) in the early diagnosis and prediction of residual renal injury. This will provide a basis for the application of NIRS in the early monitoring of residual renal injury in HD patients and offer a new method and perspective for the early diagnosis of residual renal injury in HD patients.

Hemodialysis (HD) is the main renal replacement therapy for patients with end-stage renal disease (ESRD), accounting for approximately 69% of all renal replacement therapies and 89% of all dialysis. However, factors such as unstable hemodynamics have led to the gradual loss of residual renal function (RRF) in HD patients. Research has found that 25%-67% of HD patients progress to anuria within the first 10 months of starting dialysis. The rate of loss is much faster than peritoneal dialysis（PD）, and the more frequent the dialysis sessions, the faster the loss of RRF. The loss of RRF not only affects the adequacy of dialysis and complications control but also impacts the patient's quality of life and survival. Unfortunately, until now, there have been no effective methods for early diagnosis and prediction of residual renal injury.

Traditionally, monitoring and diagnosing kidney damage have relied mainly on serum creatinine, urine output, and estimated glomerular filtration rate (eGFR). However, these indicators often occur after kidney damage has occurred, and their detection is delayed. The sensitivity for early diagnosis of kidney injury is low. By the time abnormalities are detected, the crucial treatment opportunity may have been missed. In addition, serum creatinine and other tests are susceptible to factors such as fluid dilution and reduced production in the body. Although some biomarkers for early diagnosis of acute kidney injury (AKI) have been developed domestically and internationally, most of them have not been applied in clinical practice and cannot be monitored in real-time. Moreover, these biomarkers may have significant differences in their generation between AKI and end-stage renal disease (ESRD) patients, making them unsuitable for early diagnosis and monitoring of residual renal injury in HD patients.

Near-infrared spectroscopy (NIRS) is a simple, safe, non-invasive, and real-time detection method that reflects organ perfusion by measuring changes in regional oxygen saturation. It is widely used in the diagnosis and prediction of neurological disorders, early prediction of AKI related to surgical procedures (cardiovascular, digestive, neurological, etc.), and monitoring of renal perfusion function after kidney transplantation. In theory, it can also be used for early diagnosis of residual renal injury in HD patients. This study is an exploratory research aiming to validate the value of NIRS in early diagnosis of residual renal injury by analyzing the correlation between renal oxygen saturation and urine output, as well as eGFR.

Inclusion Criteria:

• Age ≥ 18 years;
• Clinical diagnosis of end-stage renal disease requiring long-term hemodialysis treatment, with dialysis duration ≤ 3 months;
• Urine output > 500ml/day or GFR > 3ml/min/1.72m2;
• Signed and dated informed consented is obtained.

Exclusion Criteria:

• Presence of vascular access dysfunction (blood flow rate < 180ml/min);
• COPD or blood oxygen saturation < 95%;
• Severe heart failure;
• Active infection;
• Infectious disease;
• Distance between the kidney and body surface > 4cm;
• Severe pigmentation or skin lesions in the renal area;
• Patients with severe anemia;
• Patients with polycystic kidney disease;
• Expected dialysis duration < 6 months;
• Pregnancy or lactation women;
• Patients who are participating in other clinical studies, or who have participated in other clinical studies within 3 months prior to enrollment;
• Unwillingness to be followed up or poor adherence to treatment;
• Other circumstances that the investigator considers unsuitable for enrolment.

Clinical diagnosis of end-stage renal disease requiring long-term hemodialysis treatment, with dialysis duration ≤ 3 months;