The clinical problem the researchers set out to address is both common and quietly dangerous. Infants in neonatal intensive care units frequently require peripherally inserted central catheters or central venous catheters to deliver total parenteral nutrition, medications, and fluids over weeks of treatment. One recognized complication of these indwelling lines is catheter-related venous thrombosis, in which a clot forms in the vein surrounding or traversed by the device. In newborns, whose veins are tiny and whose physiology is delicate, such clots can obstruct venous return from an entire limb, causing swelling, discoloration, and in severe cases tissue damage. Detecting the problem early is difficult because the classic bedside signs, such as changes in skin color, temperature, or limb circumference, are late and unreliable indicators in very small patients.

The gold standard for confirming venous thrombosis is color Doppler flow imaging, an ultrasound technique that visualizes blood flow within vessels. But ultrasound is a snapshot, not a continuous monitor, and repeated examinations require skilled operators and the manipulation of a fragile infant. The Chinese team reasoned that near-infrared spectroscopy could fill the monitoring gap. NIRS exploits a simple physical fact: oxygenated hemoglobin and deoxygenated hemoglobin absorb near-infrared light differently. By shining light in the near-infrared range into tissue and measuring how much returns, a sensor can calculate the concentrations of oxyhemoglobin, deoxyhemoglobin, and total hemoglobin, and from those derive the tissue oxygen saturation index, abbreviated TOI. The method is already routine for monitoring cerebral and abdominal oxygenation in neonatal units, but reports of using it to monitor limb tissue oxygenation have been very limited.

The study followed two infants, each of whom developed venous thrombosis after limb catheterization. Before any conclusions could be drawn, the team first had to define what normal looked like. They established a safe TOI range for the monitored limbs of 58 to 68 percent, with a margin of plus or minus 2 percent, and set an operational alarm threshold: a drop of more than 20 percent from the baseline value would signify an anomaly requiring attention. Alongside the optical measurements, the clinicians simultaneously observed the color and temperature of the affected limb skin, and they used vascular ultrasound to comprehensively assess the thrombolytic effect of treatment. This combination allowed the researchers to compare what the light-based sensor reported with what conventional clinical assessment and imaging revealed.

The first infant was diagnosed with thrombosis of the right iliac vein, a large vessel deep in the pelvis that drains blood from the leg. The team treated the clot with urokinase, an enzyme that directly activates the fibrinolytic system to dissolve thrombus. Throughout the treatment course, NIRS sensors continuously recorded the tissue oxygen saturation index of the affected lower limb before, during, and after the therapy. The monitoring told a clear story: after 144 hours of thrombolytic treatment, the TOI of the affected limb returned to the normal range that the team had defined. At that point, clinical examination showed no abnormalities in the limb’s skin temperature or circumference, indicating that venous drainage had been restored and the optical readings had tracked the physiological recovery.

The second infant presented a different anatomical challenge: a thrombosis in the axillary vein near the subclavian vein, affecting the upper limb. Here the treatment strategy combined thrombolysis with anticoagulation, a dual approach aimed both at dissolving the existing clot and preventing new clot formation. The response was notably faster than in the first case. Following 17 hours of combined therapy, the TOI values measured in both upper limbs became balanced, meaning the previously compromised limb was once again matching its healthy counterpart in tissue oxygen saturation. Ultrasound follow-up then delivered the confirming evidence: no residual thrombus was detected, indicating that venous patency had been restored. The symmetry of the optical readings between the two arms served as a built-in control, since the healthy limb provided a live reference for what normal perfusion should look like.

Taken together, the two cases support the study’s central conclusion: the NIRS-monitored limb tissue oxygen saturation index can indicate the local venous filling status, which may facilitate the assessment of thrombolytic efficacy and the surveillance of thrombus formation. In practical terms, this means a nurse or physician could watch a number on a bedside monitor and see within minutes whether a clot is choking off venous return, whether a drop in saturation signals a new or extending thrombus, and whether a clot-dissolving drug is doing its job. The contrast between the two infants is instructive. The iliac vein thrombosis required six days of therapy before saturation normalized, while the axillary vein case resolved in under a day, and in both instances the optical trend mirrored the clinical and ultrasonographic outcome.

The technical elegance of the approach lies in what it measures. Unlike pulse oximetry, which reads arterial oxygen saturation at a fingertip or earlobe, NIRS captures venous-weighted tissue saturation, reflecting the balance between oxygen delivery and oxygen extraction in the microcirculation. When a vein is obstructed, blood backs up in the limb, capillary pressure rises, and the tissue becomes congested with deoxygenated blood, driving the TOI downward. As the clot dissolves and venous outflow is re-established, the stagnation clears and the saturation recovers. This makes the measurement particularly sensitive to the venous side of the circulation, which is precisely where catheter-related thrombosis does its damage. The technology also quantifies tissue hemoglobin concentrations, offering a window into local blood volume that complements the saturation reading.

As with any preliminary exploration, the caveats are substantial. The findings rest on only two infants, and the safe TOI range of 58 to 68 percent was established within this small cohort rather than validated across a population of newborns of different sizes, gestational ages, and clinical conditions. The researchers themselves describe the work as preliminary, and the published version is an early-release, peer-reviewed accepted manuscript subject to further edits. Larger prospective studies will be needed to confirm reference values, define alarm thresholds that balance sensitivity against false alarms, and determine whether continuous optical monitoring genuinely improves outcomes compared with standard surveillance. Questions also remain about sensor placement, motion artifact in active infants, and how conditions such as anemia or shock, which independently alter tissue saturation, might confound the thrombosis signal.

Even so, the implications for neonatal intensive care are compelling. Infants with central catheters are among the most vulnerable patients in medicine, and a noninvasive, continuous monitor that flags venous obstruction before a limb becomes visibly swollen could change the tempo of intervention. Rather than waiting for clinical signs or scheduling serial ultrasound examinations, clinicians could receive an early optical alert, confirm with targeted imaging, and begin thrombolysis with a real-time readout of its effect. The work from Hangzhou adds a new application to a technology that neonatologists already trust for brain and abdominal monitoring, and it points toward a future where the humble bedside light sensor becomes part of the standard safety net around every central line in the neonatal unit.

Subject of Research: Near-infrared spectroscopy monitoring of limb tissue oxygen saturation in neonatal catheter-related venous thrombosis

Article Title: Preliminary exploration of tissue oxygen saturation index using near-infrared spectroscopy in two infants of neonatal catheter-associated venous thrombosis

Article References: Zhu, H., Ling, Y., Dong, X., Luo, F., & Zhu, J. (2026). Preliminary exploration of tissue oxygen saturation index using near-infrared spectroscopy in two infants of neonatal catheter-associated venous thrombosis. BMC Pediatrics, 26(1), Article 908. https://doi.org/10.1186/s12887-026-07711-8

Image Credits: AI Generated

DOI: 10.1186/s12887-026-07711-8

Keywords: near-infrared spectroscopy, tissue oxygen saturation index, neonatal thrombosis, catheter-related venous thrombosis, urokinase thrombolysis, neonatal intensive care, central venous catheter, vascular ultrasound, newborn health, hemodynamics, case report, Preliminary