Near-Infrared Spectroscopy (NIRS) is a non-invasive optical technique used in medical settings. It uses near-infrared light to gather information about biological tissues. Its primary purpose is to continuously monitor tissue oxygen levels and assess blood flow. This technology evaluates the perfusion status of various organs non-invasively.
How Near-Infrared Spectroscopy Functions
NIRS operates on the principle that near-infrared light penetrates biological tissues, interacting with various components. Light is partly reflected and scattered by tissue elements, but it is primarily absorbed by specific optical pigments called chromophores. Hemoglobin, a primary chromophore in blood, absorbs near-infrared light differently depending on its oxygenation state. Oxygenated and deoxygenated hemoglobin have distinct light absorption patterns in the near-infrared spectrum (700-1100 nm). This difference allows NIRS devices to differentiate between them. By emitting near-infrared light into tissue and detecting the returning light, NIRS calculates the relative concentrations of oxygenated and deoxygenated hemoglobin. This provides real-time data on tissue oxygen saturation, offering insight into the balance between oxygen supply and demand.
Key Medical Uses of NIRS
NIRS has diverse clinical applications, providing insights into tissue oxygenation. One significant application is monitoring brain oxygenation, particularly in neonates. In preterm infants, NIRS-monitored regional cerebral oxygen saturation (rScO2) assesses brain oxygen supply and utilization, which systemic arterial oxygenation does not directly reflect. This continuous monitoring can detect potential ischemic episodes and guide interventions in neonatal critical care.
For adults, NIRS is frequently used during complex procedures like cardiac and vascular surgeries, where maintaining adequate cerebral perfusion is important. It helps clinicians observe changes in brain oxygen levels, indicating potential neurological complications. NIRS has also been explored in stroke monitoring and for assessing cerebral hemodynamics in patients with brain injury. However, factors like superficial tissues and skull thickness can affect readings. In adults with thicker skulls, near-infrared light penetration into the cerebral cortex might be limited to about 3 to 5 mm, while in neonates with thinner skulls, it can reach 10 to 15 mm.
Beyond cerebral applications, NIRS assesses muscle oxygenation, particularly in sports medicine and for individuals with peripheral artery disease (PAD). In sports science, NIRS evaluates how muscles utilize oxygen during exercise and recovery, aiding training optimization. For patients with PAD, NIRS monitors lower limb muscle oxygenation patterns during exercise interventions, evaluating improvements in de-oxygenation and re-oxygenation. This information can help tailor exercise therapy and assess treatment effectiveness.
Practical Aspects and Interpretation of NIRS
NIRS measurement is a non-invasive process, typically involving sensor placement directly on the skin over the area of interest. These sensors emit and detect near-infrared light, making the procedure comfortable. NIRS provides continuous, real-time data, allowing ongoing monitoring of tissue oxygenation.
NIRS data are often presented as numerical values or real-time graphs, showing changes in oxygenated and deoxygenated hemoglobin. Medical professionals interpret these readings within a patient’s overall clinical picture. For instance, a decrease in regional oxygen saturation might prompt further investigation or intervention to improve tissue oxygen delivery. NIRS offers a distinct advantage over pulse oximetry, which measures arterial oxygen saturation, by providing information about tissue-level oxygen uptake, including both arterial and venous blood. The technology is portable and considered safe, making it suitable for use in various clinical environments, including emergency rooms and intensive care units.