Neurological monitoring in the high-risk infant: Near-infrared spectroscopy (NIRS)

The near-infrared spectroscopy (NIRS) sensor is placed at the forehead avoiding cavities, superior sagittal sinus, intra or extra-cranial huge blood collections, or vascular malformations, if known. Scalp oedema will also influence the quality of the NIRS signal. In the smallest newborn infants and those with poor perfusion states sensor position is rotated to avoid tissue injury related to compression or heat. (7,20)

Commercial NIRS devices incorporate similar technology but different wavelengths and computational algorithms translating changes in light absorption into rStO₂ absolute values. (7) Systematic approach has evidenced huge differences in rStO₂ according to device or probe (30,36), so that device-specific reference ranges or limits have to be used.

Neonatal resuscitation after birth: Clinical assessment of the newborn infant carries high inter-observer variability particularly when scoring preterm or term infants in need of resuscitation. (37) Oxygen saturation targeting and the use of supplemental oxygen during transition remain controversial topics. (38) The use of pulse oximetry or heart rate monitoring during resuscitation has not led to improvements on the short or long-term outcomes. (39) rStO₂ and fractional oxygen extraction reference ranges and percentile charts for the interpretation of cerebral oxygenation during immediate transition to avoid hypo- and hyperoxia of the brain during resuscitation appears promising. (11,18,19) Yet, routine interventions based on rStO₂ during resuscitation need development and evaluation.

Extremely low gestational age newborn infants: Recent studies have shown an association of cerebral rStO₂ levels and clinical outcomes. (40)Low rStO₂ on the first day of life associates surrogated measures of compromised systemic blood flow and risk of intraventricular haemorrhage. (12) Impaired cerebral blood flow autoregulation assessed by NIRS and arterial blood pressure monitoring associates abnormal systemic (and cerebral) blood flow distribution, death and severe brain injury. (41,42) Cerebral oxygenation can be stabilised in the preterm infant during the first 72 hours from birth by the combined use of rStO₂-NIRS monitoring and a pathophysiological, brain oriented treatment guideline with no record of severe adverse events. (9,10) The quality of evidence supporting some of the listed statements in the intervention algorithm is generally low, however, are all routinely used in clinical care of these patients. (9) Although important early surrogate outcomes, such as aEEG at day 3 of postnatal life or neuroimaging, did not significantly differ between the study groups (43,44), post hoc analyses showed that early burden of cerebral hypoxia was significantly associated with low brain electrical activity and severity of intracranial haemorrhage. (19) So far, definitive evidence of benefit for improvement of long-term clinical outcomes is needed as the technology is not cheap, requires manipulation and additional staff time, and may have unwanted effects. (10)

PIVH: Correlations between NIRS-derived data immediately after birth and during the transitional circulation and the development of PIVH have been reported. (12–14) Timing of neurosurgical intervention in PHVD could be critical for neurodevelopment (45), and may be guided by standardised ventricular measurements by cranial ultrasound combined with cerebral NIRS and cranial Doppler. (21,22) This approach provides a better understanding of the pathophysiology and the effect of interventions on the long-term outcomes.

HIE: Cerebral hypoperfusion during the first hours after birth is followed by hyperperfusion, even during treatment with moderate hypothermia.Potential differences according to the severity of brain injury (moderate vs severe) have been identified. (15,46) NIRS measurements of oxygenation and MRI measurements of brain perfusion show good correlation. (15) Among neonates with HIE, NIRS demonstrates evolving patterns of brain oxygenation that predict favourable and adverse outcomes both in non-cooled (46) and in those who undergo therapeutic hypothermia. (23,24) As yet, widespread recommendation of NIRS monitoring alone to guide important clinical decisions in asphyxiated newborn infants cannot be made.  Used in combination with amplitude-integrated EEG increases the outcomes predictive capacity compared to either modality alone. (24–26)

Congenital heart disease (CHD): NIRS may be a useful adjunct particularly during cardiopulmonary bypass to optimise perfusion. NIRS-derived measures of systemic oxygen balance correlate with global circulatory measures and biochemical indicators of shock. (27) Algorithms have been developed to guide interventions based on rStO₂ values during the perioperative period. (28) However, the current literature on the use of NIRS alone does not demonstrate improvement in neurologic outcome. (29) Prospective data evaluating NIRS findings and relevant outcomes in this population is difficult to compare, because of the variable disease physiology, variable baseline values, and small sample sizes. These issues prevent extrapolation to wider CHD population.

Other complex surgical procedures conducted during the neonatal period, such as congenital diaphragmatic hernia or oesophageal atresia (34,35), might be additional scenarios where NIRS may guide surgeons and anaesthesiologists during the intervention procedures. A NIRS value out of normal range, or a huge change even within the normal range, may trigger the assessment of the patient’s condition when used in combination with other monitoring tools.