Review on the use and applications of Near-Infrared Spectroscopy (NIRS) in critical care patients in Neonatal Intensive Care Unit (NICU)

Abstract

Background

Near-Infrared Spectroscopy (NIRS) is a non-invasive optical technology that continuously measures oxygen-dependent changes in haemoglobin absorption, providing insights into regional cerebral oxygenation (rSO2).  By quantifying oxyhaemoglobin (cO2Hb) and deoxyhaemoglobin (cHHb) levels, NIRS offers valuable real-time data on cerebral perfusion and tissue oxygenation.

Clinical Applications of NIRS

NIRS is widely used in critical care settings, particularly during cardiac surgeries, extracorporeal membrane oxygenation (ECMO), where it detects cerebral desaturation suggesting better neurological outcomes. Unlike pulse oximetry, NIRS is effective in non-pulsatile scenarios and offers continuous, hands-free monitoring during surgeries without recalibration.

NIRS in Neonates

 In neonates, NIRS is instrumental in detecting conditions such as neonatal asphyxia and monitoring cerebral oxygenation during cardiac catheterisation and surgery.  Its accuracy is enhanced by minimal interference from extra-cranial tissue layers, allowing early detection of brain injuries and adverse neurological outcomes. Studies demonstrate its utility in assessing cerebral perfusion during ECMO, including the effects of carotid and jugular vein ligation.

NIRS in Neonatal ECMO

NIRS is especially valuable in neonates on ECMO, offering continuous, non-invasive bedside monitoring. It detects cerebral desaturation, correlates rSO2 changes with impaired cerebral autoregulation, enabling early intervention for complications such as ischaemic stroke, intracranial haemorrhage, and seizures. Studies demonstrate its utility in assessing cerebral perfusion during ECMO, including the effects of carotid and jugular vein ligation.5 Furthermore, international guidelines (ELSO) recognise NIRS as a standard monitoring tool which, in combination with continuous EEG, and cranial ultrasound plays an essential role in the early detection of acute neurological events.

Limitations of using NIRS

Despite its potential, NIRS faces challenges such as limited tissue penetration, dependence on systemic factors (e.g., low cardiac output, hypoxia, and anaemia), and algorithmic constraints. It provides relative rather than absolute values, lacks quantitative precision, and may fail to immediately reflect clinical events, raising questions about its impact on long-term outcomes.

 A lack of standardised rSO2 thresholds remains a key challenge. Studies in adults have proposed thresholds (rSO2 <50%: point to intervene, rSO2<40% or a 20% from baseline: critical.7,8 Yet, these are potentially unsuitable for neonates due to their distinct cerebral physiology. Additionally, variability in venous-to-arterial blood ratios and immature cerebral circulation complicates the interpretation of NIRS data in the neonatal population.

Conclusion

NIRS is a pivotal tool in neonatal and critical care, particularly for ECMO patients, offering real-time insights into cerebral oxygenation. However, standardised protocols and integration with complementary modalities are essential to fully realise its potential in improving long-term neuro-developmental outcomes.