The Neonatal Intensive Care Unit (NICU) provides specialized care for newborns facing health challenges, particularly those born prematurely or with complex medical conditions. Continuous monitoring is a cornerstone of care for these vulnerable infants, allowing medical teams to observe their physiological states. Near-infrared spectroscopy (NIRS) monitoring is a non-invasive technology employed in the NICU to offer real-time insights into an infant’s well-being. This tool helps clinicians assess how well oxygen is reaching and being used by specific tissues and organs.
What NIRS Measures
NIRS monitoring assesses regional tissue oxygen saturation (rSO2 or StO2), a localized measure of oxygen levels within specific tissues. This differs from pulse oximetry, which measures arterial oxygen saturation in the blood. NIRS provides a “weighted average” of oxygen saturation from arterial, capillary, and venous blood within the monitored tissue, with approximately 85% of the signal originating from venules.
Monitoring oxygen levels in specific organs, such as the brain, kidneys, or intestines, is important for critically ill infants. Insufficient oxygen delivery to these tissues can lead to damage. NIRS offers a continuous, real-time snapshot of the balance between oxygen supply and consumption in these localized areas, helping to identify potential issues like hypoxia (low oxygen) or ischemia (restricted blood flow) early.
How NIRS Works
NIRS uses near-infrared light. A sensor, placed on the infant’s skin over the area of interest, emits light in the near-infrared spectrum (700-900 nm). This light can penetrate biological tissues.
As the near-infrared light passes through the tissues, it is absorbed differently by oxygenated and deoxygenated hemoglobin. Hemoglobin, the protein in red blood cells that carries oxygen, changes its light absorption characteristics depending on its oxygenation status. By measuring the amount of light absorbed at various wavelengths, the NIRS device calculates the concentrations of oxygenated and deoxygenated hemoglobin. This allows for the determination of regional tissue oxygen saturation, offering a safe and continuous method to assess oxygen levels.
Clinical Applications in the NICU
NIRS monitoring finds broad application in the NICU, providing valuable insights into the oxygenation of various organs. Cerebral NIRS (cNIRS) monitors brain oxygenation, helping detect conditions like ischemia or hypoxemia that could impact neurological development. This helps clinicians identify subtle changes in brain perfusion and oxygenation early, allowing for timely interventions.
Splanchnic NIRS assesses gut oxygenation, useful in identifying conditions such as necrotizing enterocolitis (NEC), a serious intestinal disease affecting newborns. Early detection of compromised gut oxygenation can lead to prompt treatment, potentially improving outcomes. NIRS can also monitor kidney function by assessing renal tissue oxygenation (RrSO2). Decreased RrSO2 may suggest reduced oxygen delivery or increased consumption, prompting evaluation for acute kidney injury.
Interpreting NIRS Information
Healthcare professionals interpret NIRS readings by focusing on regional oxygen saturation (rSO2) values, expressed as a percentage. These numbers reflect the balance between oxygen delivery to the tissue and its oxygen consumption. Normal cerebral rSO2 values typically range between 55% and 85%.
Trends in NIRS readings, rather than single measurements, provide more meaningful information about an infant’s physiological status. A significant rise or fall from a patient’s established baseline, such as a change greater than 20%, can indicate underlying physiological shifts. This trending data, combined with other monitoring tools like heart rate, blood pressure, and traditional pulse oximetry, helps guide treatment decisions. NIRS provides supplementary information that aids in personalized care, allowing clinicians to adjust interventions like ventilation, fluid management, or medication based on real-time tissue oxygenation.