Abstract
Introduction:
Acute rejection remains a major cause of morbidity and graft loss after kidney transplantation, despite advances in immunosuppressive therapy. Conventional monitoring methods, such as serum creatinine, urine output, and Doppler ultrasound, detect graft dysfunction only after significant injury has occurred. Near-infrared spectroscopy (NIRS) is a noninvasive technique that continuously measures regional tissue oxygen saturation (rSO2) and may allow earlier detection of perfusion abnormalities.
Case report:
A 36-year-old male with end-stage kidney disease underwent living-donor kidney transplantation under general anesthesia with goal-directed fluid therapy. Postoperative NIRS monitoring was performed using a sensor placed over the graft site. The rSO2 was approximately 95% on postoperative day (POD) 1, decreased to 78% on POD 2, and reached a nadir of 66% on POD 3, followed by gradual recovery to 91% by POD 6. Despite the apparent improvement in NIRS values, the patient developed oliguria progressing to anuria on POD 6. A renal biopsy confirmed acute rejection, and immunosuppressive therapy was promptly intensified.
Discussion:
The early decline in rSO2 likely reflected evolving hypoperfusion, while the subsequent increase may have resulted from impaired oxygen extraction due to microvascular injury. This paradoxical trend resembles shock states, in which poor oxygen utilization leads to deceptively normal saturation levels. NIRS enables continuous, real-time assessment of graft perfusion, complementing conventional monitoring tools. However, interpretation must consider confounding factors such as tissue characteristics, light interference, and hemodynamic variability.
Conclusion/take-home message:
Near-infrared spectroscopy (NIRS) may serve as an early, noninvasive indicator of graft dysfunction and acute rejection after kidney transplantation.
Introduction
Kidney transplantation remains the gold standard treatment for end-stage kidney disease, offering superior survival and quality of life compared to dialysis (5, 7). Despite advances in immunosuppressive therapy, allograft rejection continues to pose significant challenges, with consequences ranging from hospitalization to graft failure.
Current post-transplant monitoring relies primarily on serum creatinine levels and urine output, supplemented by Doppler ultrasound when complications are suspected. However, these conventional methods detect dysfunction only after significant graft compromise has occurred, limiting opportunities for early intervention. Near-infrared spectroscopy (NIRS) offers a promising solution as a noninvasive technique providing continuous, real-time assessment of regional tissue oxygen saturation (rSO2). When allograft dysfunction occurs due to acute rejection, vascular stenosis, or thrombosis, renal hypoperfusion results in decreased tissue oxygenation potentially detectable by NIRS before clinical manifestations appear.
This case report demonstrates postoperative NIRS monitoring following kidney transplantation, where changes in tissue oxygen saturation preceded clinical signs of acute rejection, potentially serving as an early warning system for graft dysfunction.
Case description
We report a 36-year-old male patient with autosomal dominant polycystic kidney disease who had previously undergone bilateral radical nephrectomy and was maintained on hemodialysis for one year. The patient underwent living-donor kidney transplantation from a 42-year-old male donor with hypertension. Surgery was performed under general anesthesia with goal-directed fluid therapy.
Postoperative monitoring included near-infrared spectroscopy (INVOS™ system). The NIRS sensor was positioned parallel to the surgical wound, with direct contact with the skin and underneath the surgical dressing, in accordance with recommended practices to minimize signal interference. Ultrasound guidance was used to confirm appropriate sensor positioning, ensuring adequate alignment of the measurement field with the target tissue and reducing potential bias related to anatomical variability or inadequate tissue coverage.
Regarding measurement depth, NIRS devices typically interrogate tissues located approximately 1.5–3.0 cm below the skin surface, depending on the distance between light emitters and detectors.
There was no need for continuous vasopressor use beyond minimal doses, both intraoperatively and postoperatively, such as those administered at the time of graft reperfusion, when a mean arterial pressure of 80 mmHg was prioritized.
On postoperative day (POD) 1, graft rSO2 was high (95%), despite markedly elevated serum creatinine (6.2 mg/dL) and preserved urine output (13,000 mL/24 h). By POD 2, a significant decline in rSO2 was observed (78%), while serum creatinine showed initial improvement (4.1 mg/dL) and urine output decreased to 6,000 mL/24 h. The rSO2 reached its nadir on POD 3 (66%, representing a 30% reduction from baseline), coinciding with continued improvement in serum creatinine (3.0 mg/dL) but further reduction in urine output (3,500 mL/24 h).
From POD 4 to POD 6, rSO2 values gradually increased, approaching baseline levels and reaching 91% by POD 6. During this period, urine output progressively declined from 3,000 to 1,000 mL/24 h. Notably, on POD 6, despite apparent recovery of rSO2 to 91%, the patient developed oliguria progressing to anuria. By POD 8, serum creatinine was 5.0 mg/dL and acute cellular rejection (Banff IIa) was confirmed by renal biopsy (Table 1).
Table 1
| POD | NIRS rSO2 (%) | Serum creatinine (mg/dL) | Estimated urine output (mL/24 h) | Clinical notes |
|---|---|---|---|---|
| 1 | 95 | 6.2 | 13,000 | – |
| 2 | 78 | 4.1 | 6,000 | Decline in NIRS, creatinine improving |
| 3 | 66 (−30% from baseline) | 3.0 | 3,500 | NIRS nadir |
| 4–6 | Gradual recovery, up to 91 | – | 3,000–1,000 | NIRS approaching baseline |
| 6 | 91 | – | 0 | Oliguria → anuria |
| 8 | – | 5.0 | 0 | Acute cellular rejection (Banff IIa) confirmed by biopsy and intensification of immunosuppressive therapy |
Clinical timeline.
Immediate intensification of immunosuppressive therapy was initiated following biopsy confirmation. The patient expressed satisfaction with close postoperative monitoring and consented to share his experience.
Discussion
Current monitoring limitations and NIRS applications
Renal transplant monitoring currently relies on intermittent assessments with significant limitations. Serum creatinine exhibits delayed response to acute changes and cannot detect subclinical dysfunction (1). Doppler ultrasound provides only intermittent, operator-dependent assessments and cannot capture dynamic perfusion changes in real time (2).
Near-infrared spectroscopy utilizes near-infrared light (700–1,000 nm) to measure regional tissue oxygen saturation by detecting absorption spectra of oxygenated and deoxygenated hemoglobin. Unlike pulse oximetry measuring arterial saturation, NIRS provides microcirculatory information including arterioles, capillaries, and venules. Studies have shown NIRS can discriminate between living and deceased donor kidney reperfusion profiles, with lower rSO2 values associated with delayed graft function (3).
Beyond rejection monitoring, NIRS holds particular promise for detecting renal vein thrombosis, an extremely grave complication with high mortality rates that occurs in 0.5%–4% of kidney transplants. Traditional diagnostic methods often delay recognition until advanced stages when salvage becomes impossible. The continuous, dynamic, non-invasive nature of NIRS monitoring could enable early detection of this potentially fatal vascular complication through real-time assessment of venous congestion and tissue perfusion changes, offering a crucial diagnostic window before irreversible graft loss occurs.
This opens the possibility for the early initiation of treatments aimed at reversing acute rejection as rapidly as possible, thereby preventing adverse outcomes. However, there is limited evidence regarding the most appropriate therapeutic strategies prior to biopsy confirmation, due to insufficient robust data to inform therapeutic decisions. Consequently, biopsy is still frequently used to individualize and guide immunosuppressive therapy, as it relies on histological changes and standardized grading systems for this purpose (4). In this case report, immunosuppressive therapy was escalated only after biopsy confirmation, which allowed for successful treatment of acute rejection. Nevertheless, more robust studies are needed to evaluate the feasibility and safety of initiating immunosuppressive therapy for treatment of acute rejection even before biopsy confirmation.
Case analysis and pathophysiology
Our case presents a unique biphasic temporal pattern that may provide insights into the pathophysiology of acute rejection. The initial NIRS decline (POD 1–3) from 95% to 66% occurred paradoxically while creatinine levels were improving (6.2–3.0 mg/dL) and urine output was maintained. This apparent contradiction suggests that the declining rSO2 may reflect increased cellular metabolic activity and oxygen consumption by recovering tubular cells, rather than simply perfusion compromise. The metabolically active renal parenchyma was extracting more oxygen from the available blood supply, leading to decreased tissue oxygen saturation despite adequate perfusion and improving function. This early metabolic signal preceded clinical signs of rejection by 4–6 days, representing a potentially valuable therapeutic window where cellular dysfunction could be detected before conventional markers deteriorated.
The subsequent NIRS “recovery” to 91% by POD 6 (Figure 1), paradoxically coinciding with clinical deterioration, represents a particularly intriguing phenomenon. We hypothesize this apparent recovery reflects impaired tissue oxygen extraction rather than true perfusion restoration. In rejection-related microvascular injury, damaged tubular cells lose their ability to effectively utilize oxygen, resulting in relatively preserved tissue oxygen saturation despite ongoing cellular dysfunction. This mechanism is analogous to distributive shock states, where poor microcirculation prevents adequate oxygen offloading, leading to misleadingly elevated oxygen saturation despite tissue hypoxia.
Figure 1
Graph showing the variation of tissue oxygen saturation (NIRS — near-infrared spectroscopy) over time after kidney transplant.
The temporal dissociation suggests different pathophysiological processes dominate at different time points: early vascular compromise detectable by NIRS, followed by cellular dysfunction manifesting clinically despite apparent tissue oxygenation recovery.
Hemodynamic interpretation of NIRS values was systematically integrated with concomitant clinical and laboratory data. Laboratory tests, including hemoglobin concentrations, were obtained according to the unit's routine protocol, with a frequency of twice daily during the patient's stay in the closed unit. In parallel, the use of vasoactive drugs was continuously documented, allowing temporal correlation between systemic hemodynamic interventions and regional tissue oxygenation changes.
This integrated approach—combining continuous NIRS monitoring, serial laboratory assessments, and detailed clinical data—strengthens the physiological interpretation of the findings, reduces the risk of overinterpretation of isolated measurements, and supports the plausibility of the observed associations between regional perfusion, therapeutic interventions, and clinical evolution.
Clinical implications and limitations
This case suggests NIRS may provide early detection of perfusion abnormalities preceding clinical signs, offering a potentially valuable therapeutic window. However, the complex temporal relationship indicates that interpretation algorithms must account for biphasic rejection-related perfusion changes.
Several limitations must be acknowledged. We did not establish baseline NIRS values or validate sensor positioning through alternative imaging. Technical factors that may have influenced measurements include potential sensor malposition over the graft, variable skin thickness affecting signal penetration, and progressive wound healing changes that could have altered tissue optical properties and falsely influenced rSO2 values over time. The single-sensor approach may have missed regional perfusion variations, and we lacked correlation with other perfusion methods such as contrast-enhanced ultrasound. Additionally, external factors like ambient light interference and patient movement could have affected signal quality. The retrospective analysis limits determination of optimal threshold values for clinical intervention.
Future directions
Continuous NIRS monitoring for first 7 days post-transplant
Alert thresholds: >20% decline from baseline or absolute values <70%
Integration with conventional monitoring (creatinine, urine output, Doppler)
Mandatory clinical correlation before intervention decisions
Prospective validation studies with larger cohorts to establish evidence-based thresholds
Multi-center trials determining optimal sensor positioning protocols
Pathophysiological studies correlating NIRS patterns with histological changes
Development of artificial intelligence algorithms for pattern recognition
Before widespread adoption, consensus guidelines must be developed for sensor placement, baseline establishment, threshold definition, and integration with existing diagnostic algorithms.
Conclusion
This case demonstrates both the promise and complexity of NIRS monitoring in kidney transplantation. While successfully detecting early perfusion abnormalities, the unexpected recovery pattern during ongoing rejection highlights the need for sophisticated interpretation algorithms accounting for transplant rejection's unique pathophysiology. Future research should focus on establishing evidence-based protocols that reliably translate NIRS findings into clinical decisions, ultimately improving early detection and management of graft dysfunction.
Statements
Data availability statement
The original contributions presented in the study are included in the article/Supplementary Material, further inquiries can be directed to the corresponding author.
Ethics statement
The requirement for ethical approval was waived by Hospital CopaStar (Rio de Janeiro) for this case report, as the institution does not require ethical committee review for single-patient case reports. The study was conducted in accordance with local legislation and institutional requirements. The participant provided written informed consent to participate in this study. Written informed consent was obtained from the individual for the publication of any potentially identifiable images or data included in this article.
Author contributions
HD: Project administration, Writing – original draft, Writing – review & editing. JR: Conceptualization, Data curation, Investigation, Methodology, Project administration, Supervision, Writing – original draft, Writing – review & editing. VF: Conceptualization, Data curation, Investigation, Methodology, Project administration, Supervision, Writing – original draft, Writing – review & editing, Resources, Validation.
Funding
The author(s) declared that financial support was not received for this work and/or its publication.
Acknowledgments
We thank the nephrology, anesthesiology, and nursing teams for clinical management and the transplant unit for monitoring support.
Conflict of interest
The author(s) declared that this work was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
Generative AI statement
The author(s) declared that generative AI was used in the creation of this manuscript. grammar correction.
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Summary
Keywords
acute rejection, case report, continuous monitoring, graft monitoring, near-infrared spectroscopy (NIRS), postoperative care, renal transplantation
Citation
Dias H, Rossi JV and Felippe V (2026) Near-infrared spectroscopy monitoring in kidney transplantation: early detection of acute rejection—a case report. Front. Anesthesiol. 5:1730512. doi: 10.3389/fanes.2026.1730512
Received
22 October 2025
Revised
17 December 2025
Accepted
02 January 2026
Published
23 January 2026
Volume
5 - 2026
Edited by
Hua Chen, Guangxi Normal University, China
Reviewed by
Penghui Cheng, China Pharmaceutical University, China
Shuping Zhang, Hengyang Normal University, China
Updates
Copyright
© 2026 Dias, Rossi and Felippe.
This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
* Correspondence: Hiorrana Dias hiorrana.dias@hotmail.com
Disclaimer
All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article or claim that may be made by its manufacturer is not guaranteed or endorsed by the publisher.