Assessment of the hypoxic–ischemic encephalopathy in neonates using non-invasive near-infrared spectroscopy

Metabolic brain measurements in the newborn: Advances in optical technologies

Neonatal monitoring in neonatal intensive care is pushing the technological boundaries of newborn brain monitoring in order to improve patient outcome. There is an urgent need of a cot side, real time monitoring for assessment of brain injury severity and neurodevelopmental outcome, in particular for term newborn infants with hypoxic-ischemic brain injury. This topical review discusses why brain tissue metabolic monitoring is important in this group of infants and introduces the currently used neuromonitoring techniques for metabolic monitoring in the neonatal intensive care unit (NICU). New optical techniques that can monitor changes in brain metabolism together with brain hemodynamics at the cot side are presented. Early studies from these emerging technologies have demonstrated their potential to deliver continuous information regarding cerebral physiological changes in sick newborn infants in real time. The promises of these new tools as well as their potential limitations are discussed.

Cerebral Near Infrared Spectroscopy Monitoring in Term Infants With Hypoxic Ischemic Encephalopathy-A Systematic Review

Background: Neonatal hypoxic ischemic encephalopathy (HIE) remains a significant cause of mortality and morbidity worldwide. Cerebral near infrared spectroscopy (NIRS) can provide cot side continuous information about changes in brain hemodynamics, oxygenation and metabolism in real time.

Objective: To perform a systematic review of cerebral NIRS monitoring in term and near-term infants with HIE.

Search Methods: A systematic search was performed in Ovid EMBASE and Medline database from inception to November 2019. The search combined three broad categories: measurement (NIRS monitoring), disease condition [hypoxic ischemic encephalopathy (HIE)] and subject category (newborn infants) using a stepwise approach as per PRISMA guidance.

Selection Criteria: Only human studies published in English were included.

Data Collection and Analysis: Two authors independently selected, assessed the quality, and extracted data from the studies for this review.

Results: Forty-seven studies on term and near-term infants following HIE were identified. Most studies measured multi-distance NIRS based cerebral tissue saturation using monitors that are referred to as cerebral oximeters. Thirty-nine studies were published since 2010; eight studies were published before this. Fifteen studies reviewed the neurodevelopmental outcome in relation to NIRS findings. No randomized study was identified.

Conclusion: Commercial NIRS cerebral oximeters can provide important information regarding changes in cerebral oxygenation and hemodynamics following HIE and can be particularly helpful when used in combination with other neuromonitoring tools. Optical measurements of brain metabolism using broadband NIRS and cerebral blood flow using diffuse correlation spectroscopy add additional pathophysiological information. Further randomized clinical trials and large observational studies are necessary with proper study design to assess the utility of NIRS in predicting neurodevelopmental outcome and guiding therapeutic interventions.

Oxygen dependency of mitochondrial metabolism indicates outcome of newborn brain injury

There is a need for a method of real-time assessment of brain metabolism during neonatal hypoxic-ischaemic encephalopathy (HIE). We have used broadband near-infrared spectroscopy (NIRS) to monitor cerebral oxygenation and metabolic changes in 50 neonates with HIE undergoing therapeutic hypothermia treatment. In 24 neonates, 54 episodes of spontaneous decreases in peripheral oxygen saturation (desaturations) were recorded between 6 and 81 h after birth. We observed differences in the cerebral metabolic responses to these episodes that were related to the predicted outcome of the injury, as determined by subsequent magnetic resonance spectroscopy derived lactate/N-acetyl-aspartate. We demonstrated that a strong relationship between cerebral metabolism (broadband NIRS-measured cytochrome-c-oxidase (CCO)) and cerebral oxygenation was associated with unfavourable outcome; this is likely to be due to a lower cerebral metabolic rate and mitochondrial dysfunction in severe encephalopathy. Specifically, a decrease in the brain tissue oxidation state of CCO greater than 0.06 µM per 1 µM brain haemoglobin oxygenation drop was able to predict the outcome with 64% sensitivity and 79% specificity (receiver operating characteristic area under the curve = 0.73). With further work on the implementation of this methodology, broadband NIRS has the potential to provide an early, cotside, non-invasive, clinically relevant metabolic marker of perinatal hypoxic-ischaemic injury.

Preterm Hypoxic-Ischemic Encephalopathy

Hypoxic-ischemic encephalopathy (HIE) is a recognizable and defined clinical syndrome in term infants that results from a severe or prolonged hypoxic-ischemic episode before or during birth. However, in the preterm infant, defining hypoxic-ischemic injury (HII), its clinical course, monitoring, and outcomes remains complex. Few studies examine preterm HIE, and these are heterogeneous, with variable inclusion criteria and outcomes reported. We examine the available evidence that implies that the incidence of hypoxic-ischemic insult in preterm infants is probably higher than recognized and follows a more complex clinical course, with higher rates of adverse neurological outcomes, compared to term infants. This review aims to elucidate the causes and consequences of preterm hypoxia-ischemia, the subsequent clinical encephalopathy syndrome, diagnostic tools, and outcomes. Finally, we suggest a uniform definition for preterm HIE that may help in identifying infants most at risk of adverse outcomes and amenable to neuroprotective therapies.

NIRS study of cerebral oxygenation and hemodynamics in neonate at birth

To study the changes of cerebral oxygenation and hemodynamics in normal neonates at 2-5 min post-birth and understand the effects of pregnancy-induced hypertension (PIH) upon cerebral oxygenation and hemodynamics in newborn neonates. The near infrared spectroscopy (NIRS) was employed to measure the absolute quantity of brain tissue oxygen saturation (rSO2) in newborn neonates and the changes of concentrations of deoxyhemoglobin (Hb) and oxygenation hemoglobin (HbO2) with time relative to initial values to further obtain the changes of total hemoglobin (tHb) and cerebral perfusion (denoted by HbD). In normal neonates at 2-5 min post-birth, rSO2 increased while tHb remained relatively stable and HbD increased. In neonates born of PIH mothers at 3-5 min post-birth, the changes of tHb were markedly higher than those in the normal infants, p<0.05; at 2-5 min post-birth, the changes were markedly lower than the normal term infants. We concluded that NIRS can detect the changes of cerebral oxygenation and blood flow in a non-invasive and effective way.

Near-infrared spectroscopy assessment of cerebral oxygen metabolism in the developing premature brain

Little is known about cerebral blood flow, cerebral blood volume (CBV), oxygenation, and oxygen consumption in the premature newborn brain. We combined quantitative frequency-domain near-infrared spectroscopy measures of cerebral hemoglobin oxygenation (SO(2)) and CBV with diffusion correlation spectroscopy measures of cerebral blood flow index (BF(ix)) to determine the relationship between these measures, gestational age at birth (GA), and chronological age. We followed 56 neonates of various GA once a week during their hospital stay. We provide absolute values of SO(2) and CBV, relative values of BF(ix), and relative cerebral metabolic rate of oxygen (rCMRO(2)) as a function of postmenstrual age (PMA) and chronological age for four GA groups. SO(2) correlates with chronological age (r=-0.54, P value ≤0.001) but not with PMA (r=-0.07), whereas BF(ix) and rCMRO(2) correlate better with PMA (r=0.37 and 0.43, respectively, P value ≤0.001). Relative CMRO2 during the first month of life is lower when GA is lower. Blood flow index and rCMRO(2) are more accurate biomarkers of the brain development than SO(2) in the premature newborns.

The utility of amplitude-integrated EEG and NIRS measurements as indices of hypoxic ischaemia in the newborn pig

OBJECTIVE

The early detection and stratification of potential hypoxic ischaemia (HI) injury in neonates are crucial for reducing the risk of neural disability. This study investigates early changes in brain function caused by acute HI of varying severities in the neonatal pig.

METHODS

Two non-invasive techniques, amplitude-integrated electroencephalogram (aEEG) and near-infrared spectroscopy (NIRS), were used to monitor electrocortical and cerebral haemodynamic function, respectively. The fraction of inspired oxygen (FiO(2)) was varied to produce different HI severities. The sensitivity and HI correlation of these methods were systematically analysed to assess their abilities to both detect injury early and assess HI severity accurately.

RESULTS

The tissue oxygen index measured via NIRS detected acute changes in cerebral oxygenation and was highly sensitive to HI (sensitivity=0.97), whereas aEEG was comparatively insensitive to HI. On the other hand, aEEG measurements correlated well with FiO(2) during the entire HI event as well as the 3-h recovery period (R=0.43-0.61). NIRS measurements did not correlate well with FiO(2).

CONCLUSIONS

Parameters measured via aEEG and NIRS displayed different time profiles during and following the HI event.

SIGNIFICANCE

These results highlight the potential advantage of using aEEG and NIRS in conjunction to monitor neonatal brain function, and provide an objective and rigorous method for the characterisation of cerebral function both during and following HI insults.

Advances in near-infrared spectroscopy to study the brain of the preterm and term neonate

This article reviews tissue oximetry and imaging to study the preterm and newborn infant brain by near-infrared spectroscopy. These two technologies are now advanced; nearly 100 reports on their use in newborn infants have been published, and commercial instruments are available. The precision of oximetry, however, is a limitation for its clinical use of assessing cerebral oxygenation. Imaging of brain function needs very well defined protocols for sensory stimulation as well as signal analysis to provide meaningful results.

The brains of very preterm newborns in clinically stable condition may be hyperoxygenated

OBJECTIVE

The objective was to compare cerebral oxygenation in preterm newborns with that in healthy term newborns.

METHODS

Forty-six preterm newborns with gestational ages of <33 weeks and 25 healthy term newborns were included. The cerebral tissue oxygenation index (c-TOI) was measured by using near-infrared spectroscopy in clinical steady state on the first day of life (median age: 19.2 hours). The mean gestational ages and birth weights in the 2 groups were 29.1 +/- 2.6 weeks versus 39.7 +/- 1.3 weeks and 1307 +/- 437 g versus 3484 +/- 346 g, respectively. Three preterm infants needed mechanical ventilation and 11 received inotropic drugs. Later, 3 preterm infants developed intraventricular hemorrhage and 2 infants died. All term infants were healthy newborns recruited in the maternity ward.

RESULTS

There was a significant difference in c-TOI (preterm: 78.6% [95% confidence interval: 76.9%-80.3%]; term: 74.7% [95% confidence interval: 72.3%-77.1%]). Preterm newborns had significantly lower fractional tissue oxygen extraction, which suggests lower oxygen extraction in this group. There was no significant correlation between head size and c-TOI. The mean peripheral oxygen saturation was 95% in both groups. The median blood Pco(2) for the preterm infants was 6.1 kPa (range: 3.4-7.3 kPa).

CONCLUSIONS

Cerebral oxygenation on the first day of life was higher in a group of relatively healthy, very preterm infants in stable condition, compared with healthy term newborns. Slightly elevated blood Pco(2) could be the explanation. Prematurity itself does not seem to dispose preterm infants to global cerebral hypoxia.

Cerebral hypoxic ischemia at different cerebral oxygen saturations in piglets: amplitude-integrated EEG study

OBJECTIVE

the objective of present paper was to study the amplitude-integrated EEG (aEEG) in hypoxic ischemic (HI) animal models and to test the reliability of aEEG method when used to monitor cerebral injuries.

METHOD

HI animal models were constructed and classified into mild, moderate and severe cerebral oxygen saturation groups according to regional oxygen saturation (rSO(2)) in brains. Then aEEG waveforms were obtained from raw EEG data using digital signal processing.

RESULT

aEEG reflected cerebral functions consistently and accurately at different cerebral rSO(2) levels. aEEG waveforms rarely changed in the group of mild HI; they dropped but recovered in moderate HI group; and aEEG maintained very low after HI in the cases when severe HI happened.

CONCLUSION

aEEG method could monitor cerebral functions directly, accurately and consistently. It is a reliable tool to continuously evaluate cerebral injuries.

Correlation of cerebral Near-infrared spectroscopy (cNIRS) and neurological markers in critically ill children

OBJECTIVE

To correlate regional brain saturations (RSO(2)) measured by cerebral Near-infrared spectroscopy (cNIRS) with serological markers indicative of neurological injury (neuron-specific enolase (NSE) and S100beta).

METHODS

Children with at least one organ failure who were undergoing cNIRS monitoring were eligible for enrollment, while children with hyperbilirubinemia and cyanotic heart disease were excluded. Children were further analyzed based on the presence of an acute neurological injury (defined as hypoxic/ischemic injury after cardiac arrest, status epilepticus, meningitis, encephalopathy) as well as survival. RSO(2) was measured continuously (every 30 s) and averages were obtained at 6 h and 24 h epochs prior to serum collection (E6 and E24, respectively). Serum was collected for NSE and S100beta, which were both determined by ELISA. Serum from children undergoing evaluation for fever in the Emergency department served as serological controls. Correlations were determined using the Pearson Product Moment Correlations.

RESULTS

A total of 26 children underwent cNIRS monitoring for a total of 47 days. Overall NSE was greater in critically ill children compared to controls, as well as in all subsets of children analyzed (acute CNS injuries, no acute CNS injuries, survivors and non-survivors). S100beta tended to be greater in critically ill children, but this did not reach statistical significance. Average RSO(2) in E6 and E24 was 68.0% +/- 1.5 and 68.6% +/- 1.6, respectively, in a total of 131,036 measurements and E6 RSO(2) was strongly, negatively correlated with S100beta in children with acute neurological injuries.

CONCLUSIONS

This is the first study to correlate averaged RSO(2) measured by cNIRS with neurological injury markers in critically ill children. We believe that this data can be used to establish thresholds for RSO(2) that can be tested in future trials to determine if this technology is predictive of long-term neurological outcome.

Research on the relationship between brain anoxia at different regional oxygen saturations and brain damage using near-infrared spectroscopy

The objective of this paper is to investigate the difference in physiological parameters, EEG and morphology of brain tissues in newborn pigs with different regional oxygen saturations of brain (rSO(2)) and provide a basis for the determination of brain injury and degree of injury with the rSO(2) in clinical practice. A noninvasive near-infrared spectroscopy (NIRS) technique was used to monitor the rSO(2) of 27 newborn pigs. After mechanical ventilation and inhalation of 3-11% oxygen for 30 min by the newborn pigs, the pigs were grouped according to the rSO(2) in the brain caused by inhalation of different concentrations of oxygen. There were six animals each in rSO(2) < 30%, 30-35%, 35-40%, 40-50% groups and three animals in the rSO(2) > 60% group (normal control). The physiological parameters and the EEG were monitored during the experiment. The animals were sacrificed by decollation at 72 hours after brain injury, and light microscope examination and pathological analysis of the ultrastructure were conducted on the brain tissues in the CA1 zone of hippocampi. In rSO(2) > 40% groups, the mean arterial pressure (MAP) was stable and there were no significant changes in blood lactic acid, amplitudes of the EEG, light microscopic findings and ultrastructure after hypoxia. When the rSO(2) was between 30% and 40%, the MAP was stable, the level of blood lactic acid increased, metabolic acidosis occurred, there was no significant change in the amplitudes of the EEG, there were ischemic changes in brain tissues under a light microscope and there was an injury of mitochondria in the neurons in the CA1 zone of hippocampi. When the rSO(2) was less than 30%, circulatory failure occurred, the level of blood lactic acid increased, there was serious metabolic acidosis, the amplitudes of the EEG significantly decreased, there were vacuolization and broken fragments of cells under the light microscope and the mitochondria in the neurons in the CA1 zone of hippocampi were seriously injured. Under varying degrees of hypoxia, when the rSO(2) is between 30% and 40%, brain injury occurs and the functional zones of mitochondria are injured in newborn pigs. When the rSO(2) is less than 30%, the brain functions are seriously abnormal, and the serious morphological impairment in the functional zones of mitochondria is the basis for the disturbance of energy metabolism in brain neurocytes after hypoxia and the sequelae of the nervous system.

Cerebral oxygenation during hypoxia and resuscitation by using near-infrared spectroscopy in newborn piglets

BACKGROUND

Hypoxic events and cardiac arrest may cause brain damage in critical infants. This study investigated cerebral tissue oxygenation and oxygen extraction in a piglet model of hypoxic events, cardiac arrest and effects of resuscitation.

METHODS

For the hypoxia experiment, anesthetized newborn piglets were randomized to a hypoxia group (n = 8) with decreasing ventilatory rate to 0, and a control group (n = 8) with no hypoxic conditions. Regional cerebral tissue oxygen saturation (rScO2, detected by near-infrared spectroscopy) and oxygen saturation were recorded every 5 minutes for 100 minutes. Fractional cerebral tissue oxygen extraction (FTOE) was calculated as (arterial oxygen saturation [SaO2] - rScO2)/SaO2. For the resuscitation experiment, animals were grouped as hypoxia-no CPR (n = 4), control-no CPR (n = 4), and control-CPR (n = 4) after cardiac arrest. Standard cardiopulmonary resuscitation (CPR) was performed on the control-CPR group and observed for 30 minutes.

RESULTS

Immediate and significant changes in rScO2, and gradual changes in FTOE were observed during the hypoxia experiment. In the resuscitation experiment, no significant differences in rScO2 were found between groups. However, the highest FTOE was observed in the control-CPR group.

CONCLUSION

Noninvasive monitoring of rScO2 and evaluating FTOE changes during hypoxia and resuscitation may help clinicians evaluate brain tissue oxygenation and viability.

Validation of a noninvasive neonatal optical cerebral oximeter in veno-venous ECMO patients with a cephalad catheter

INTRODUCTION

Cerebral Oximetry is an optical technique that allows for noninvasive and continuous monitoring of brain oxygenation by determining tissue oxygen saturation (SctO2). In conjunction with pulse oximetry, cerebral oximetry offers a promising method to estimate cerebral venous oxygen saturation (SvO2).

OBJECTIVE

The aim of this study was to validate the cerebral oximetry measurements with the cerebral oxygen saturation measured from blood drawn in neonates on veno-venous ECMO with existing cephalad catheter with a prototype neonatal cerebral oximeter developed by CAS Medical Systems (Branford, CT, USA).

STUDY DESIGN

After obtaining informed consent, neonates undergoing VV-ECMO with cephalad catheterization were monitored by the CAS cerebral oximeter. Cephalad blood samples were periodically obtained to validate the monitor's accuracy.

RESULTS

Seventeen neonates were studied with 1718 h of cerebral oximetry data collected. Compared to the reference values, the bias+/-precision for cerebral oximetry SctO2 was 0.4+/-5.1% and derived SvO2 was 0.6+/-7.3%.

CONCLUSION

We recommend the use of this noninvasive method as an alternative to blood draws for cerebral venous saturation measurements in neonates requiring extracorporeal life support.

Near-infrared spectroscopy in the detection of regional tissue oxygenation during hypoxic events in preterm infants undergoing critical care

OBJECTIVES

To determine whether pulse oximetry-detected episodes of desaturation are associated with impairment of cerebral and somatic (renal) tissue oxygenation in mechanically ventilated preterm neonates.

DESIGN

Observational cross-sectional study.

SETTING

Neonatal intensive care unit of a university-affiliated children's hospital.

PATIENTS

Ten mechanically ventilated preterm (gestational age 24-32 wks) infants.

INTERVENTIONS

In addition to the traditional monitoring of hemodynamic variables that included pulse oximetry (Sao2), near-infrared spectroscopy (NIRS) was used to evaluate the cerebral and somatic (renal) tissue oxygen saturation (rSO2C and rSO2R, respectively).

MEASUREMENTS AND MAIN RESULTS

A total of 40 rSO2C and rSO2R measurements were simultaneously recorded: 20 during hypoxic events when the Sao2 was </=80% for >/=4 secs (cases) and generally ranged between 70% and 80%, and 20 measurements when the Sao2 was >/=85% (paired controls). Additionally, the fractional oxygen extraction (FOE) from the cerebral (FOEC) and renal (FOER) tissue was calculated. All the measurements were made under steady conditions during a 2-hr period. The rSO2C, rSO2R, FOEC, and FOER among the cases (Sao2 </= 80%) and controls (Sao2 >/= 85%) were compared using the paired Student's t-test. Both rSO2C and rSO2R during the desaturation episodes were lower than in the controls (51.6 +/- 6.3% vs. 66.2 +/- 10.2%, p < .0001 and 61.1 +/- 6.8% vs. 80.1 +/- 10.0%, p < .0001, respectively). The FOEC during the hypoxic episodes was comparable with control levels but increased in renal tissue. However, during two of the desaturation episodes (10%), the rSO2C and FOEC levels (which were <44% and >0.47, respectively) may reflect compromised tissue oxygen supply.

CONCLUSIONS

In the majority of mechanically ventilated preterm neonates, the reduction in cerebral and renal tissue oxygenation associated with short periods of decreased arterial saturation to 70-80% does not significantly compromise oxygen utilization in the cerebral tissue but increases oxygen extraction in the renal tissue, which might cause ischemic tissue injury following a further reduction in oxygen delivery.

Monitoring cerebral oxygen saturation during cardiopulmonary bypass using near-infrared spectroscopy: the relationships with body temperature and perfusion rate

During cardiopulmonary bypass (CPB) because of weak arterial pulsation, near-IR spectroscopy (NIRS) is almost the only available method to monitor cerebral oxygenation noninvasively. Our group develops a NIRS oximeter to monitor regional cerebral oxygenation especially its oxygen saturation (rScO2). To achieve optimal coupling between the sensor and human brain, the distances between the light source and the detectors on it are properly chosen. The oximeter is calibrated by blood gas analysis, and the results indicate that its algorithm is little influenced by either background absorption or overlying tissue. We used it to measure the rScO2 of 15 patients during CPB. It is shown that rScO2 is negatively correlated with body temperature and positively with perfusion rate. There are two critical stages during CPB when rScO2 might be relatively low: one is the low-perfusion-rate stage, the other is the early rewarming stage. During cooling, the changes of total hemoglobin concentration (C(tHb)) compared with its original value is also monitored. It is shown that C(tHb) decreases to a small extent, which may mainly reflect cerebral vasoconstriction induced by cooling. All these results indicate that NIRS can be used to monitor cerebral oxygenation to protect cerebral tissue during CPB.