Cerebral blood volume measurement using near-infrared time-resolved spectroscopy and histopathological evaluation after hypoxic-ischemic insult in newborn piglets

Ultrasound Diagnosis and Near-Infrared Spectroscopy in the Study of Encephalopathy in Neonates Born under Asphyxia: Narrative Review

Brain injury resulting from adverse events during pregnancy and delivery is the leading cause of neonatal morbidity and disability. Surviving neonates often suffer long-term motor, sensory, and cognitive impairments. Birth asphyxia is among the most common causes of neonatal encephalopathy. The integration of ultrasound, including Doppler ultrasound, and near-infrared spectroscopy (NIRS) offers a promising approach to understanding the pathology and diagnosis of encephalopathy in this special patient population. Ultrasound diagnosis can be very helpful for the assessment of structural abnormalities associated with neonatal encephalopathy such as alterations in brain structures (intraventricular hemorrhage, infarcts, hydrocephalus, white matter injury) and evaluation of morphologic changes. Doppler sonography is the most valuable method as it provides information about blood flow patterns and outcome prediction. NIRS provides valuable insight into the functional aspects of brain activity by measuring tissue oxygenation and blood flow. The combination of ultrasonography and NIRS may produce complementary information on structural and functional aspects of the brain. This review summarizes the current state of research, discusses advantages and limitations, and explores future directions to improve applicability and efficacy.

Hydrogen gas can ameliorate seizure burden during therapeutic hypothermia in asphyxiated newborn piglets

BACKGROUND

We previously reported that hydrogen (H2) gas combined with therapeutic hypothermia (TH) improved short-term neurological outcomes in asphyxiated piglets. However, the effect on seizure burden was unclear. Using amplitude-integrated electroencephalography (aEEG), we compared TH + H2 with TH alone in piglets 24 h after hypoxic-ischemic (HI) insult.

METHODS

After a 40-min insult and resuscitation, 36 piglets ≤24 h old were divided into three groups: normothermia (NT, n = 14), TH alone (33.5 ± 0.5 °C, 24 h, n = 13), and TH + H2 (2.1-2.7% H2 gas, 24 h, n = 9). aEEG was recorded for 24 h post-insult and its background pattern, status epilepticus (SE; recurrent seizures lasting >5 min), and seizure occurrence (Sz; occurring at least once but not fitting the definition of SE) were evaluated. Background findings with a continuous low voltage and burst suppression were considered abnormal.

RESULTS

The percentage of piglets with an abnormal aEEG background (aEEG-BG), abnormal aEEG-BG+Sz and SE was lower with TH + H2 than with TH at 24 h after HI insult. The duration of SE was shorter with TH + H2 and significantly shorter than with NT.

CONCLUSIONS

H2 gas combined with TH ameliorated seizure burden 24 h after HI insult.

IMPACT

In this asphyxiated piglet model, there was a high percentage of animals with an abnormal amplitude-integrated electroencephalography background (aEEG-BG) after hypoxic-ischemic (HI) insult, which may correspond to moderate and severe hypoxic-ischemic encephalopathy (HIE). Therapeutic hypothermia (TH) was associated with a low percentage of piglets with EEG abnormalities up to 6 h after HI insult but this percentage increased greatly after 12 h, and TH was not effective in attenuating seizure development. H2 gas combined with TH was associated with a low percentage of piglets with an abnormal aEEG-BG and with a shorter duration of status epilepticus at 24 h after HI insult.

Advanced Neuromonitoring Modalities on the Horizon: Detection and Management of Acute Brain Injury in Children

Timely detection and monitoring of acute brain injury in children is essential to mitigate causes of injury and prevent secondary insults. Increasing survival in critically ill children has emphasized the importance of neuroprotective management strategies for long-term quality of life. In emergent and critical care settings, traditional neuroimaging modalities, such as computed tomography and magnetic resonance imaging (MRI), remain frontline diagnostic techniques to detect acute brain injury. Although detection of structural and anatomical abnormalities remains crucial, advanced MRI sequences assessing functional alterations in cerebral physiology provide unique diagnostic utility. Head ultrasound has emerged as a portable neuroimaging modality for point-of-care diagnosis via assessments of anatomical and perfusion abnormalities. Application of electroencephalography and near-infrared spectroscopy provides the opportunity for real-time detection and goal-directed management of neurological abnormalities at the bedside. In this review, we describe recent technological advancements in these neurodiagnostic modalities and elaborate on their current and potential utility in the detection and management of acute brain injury.

Impact of hydrogen gas inhalation during therapeutic hypothermia on cerebral hemodynamics and oxygenation in the asphyxiated piglet

We previously reported the neuroprotective potential of combined hydrogen (H₂) gas ventilation therapy and therapeutic hypothermia (TH) by assessing the short-term neurological outcomes and histological findings of 5-day neonatal hypoxic-ischemic (HI) encephalopathy piglets. However, the effects of H₂ gas on cerebral circulation and oxygen metabolism and on prognosis were unknown. Here, we used near-infrared time-resolved spectroscopy to compare combined H₂ gas ventilation and TH with TH alone. Piglets were divided into three groups: HI insult with normothermia (NT, n = 10), HI insult with hypothermia (TH, 33.5 ± 0.5 °C, n = 8), and HI insult with hypothermia plus H₂ ventilation (TH + H₂, 2.1-2.7%, n = 8). H₂ ventilation and TH were administered and the cerebral blood volume (CBV) and cerebral hemoglobin oxygen saturation (ScO₂) were recorded for 24 h after the insult. CBV was significantly higher at 24 h after the insult in the TH + H₂ group than in the other groups. ScO₂ was significantly lower throughout the 24 h after the insult in the TH + H₂ group than in the NT group. In conclusion, combined H₂ gas ventilation and TH increased CBV and decreased ScO₂, which may reflect elevated cerebral blood flow to meet greater oxygen demand for the surviving neurons, compared with TH alone.

Cerebral hemodynamic response during the resuscitation period after hypoxic-ischemic insult predicts brain injury on day 5 after insult in newborn piglets

Perinatal hypoxic-ischemic brain injury of neonates remains a significant problem worldwide. During the resuscitation period, changes in cerebral hemoglobin oxygen saturation (ScO₂) have been identified by near-infrared spectroscopy (NIRS). However, in asphyxiated neonates, the relationship between these changes and brain injury is not known. Three-wavelength near-infrared time-resolved spectroscopy, an advanced technology for NIRS, allows for the estimation of ScO₂ and cerebral blood volume (CBV). Here, we studied changes in ScO₂ and CBV during the resuscitation period after hypoxic-ischemic insult and the relationship between these changes after insult and histopathological brain injuries on day 5 after insult using an asphyxiated piglet model. Of 36 newborn piglets subjected to hypoxic-ischemic insult, 29 were analyzed. ScO₂ and CBV were measured 0, 5, 10, 15, and 30 min after the insult. Brain tissue was histologically evaluated on day 5. ScO₂ and CBV increased immediately after the insult, reached a peak, and then maintained a consistent value. The increase in CBV 5 to 30 min after the insult was significantly correlated with histopathological injury scores. However, there was no correlation with ScO₂. In conclusion, an increase in CBV within 30 min after hypoxic-ischemic insult reflects the histopathological brain injury on day 5 after insult in a piglet model.

Hypothermia cannot ameliorate renal fibrosis after asphyxia in the newborn piglet

BACKGROUND

The effects of therapeutic hypothermia (TH) on renal function are not widely reported, especially in longer term animal models. The hypothesis of this study was that TH of the kidneys of hypoxic-ischemic newborn piglets would reduce pathological renal fibrosis.

METHODS

Twenty-five newborn piglets obtained within 24 h of birth were classified into a control group (n = 5), an hypoxic insult with normothermia (HI-NT) group (n = 12), and an hypoxic insult with TH (HI-TH) group (33.5 °C ± 0.5 °C for 24 h; n = 8). Five days after the insult, all piglets were sacrificed under deep anesthesia by isoflurane inhalation. The kidneys were perfused with phosphate-buffered paraformaldehyde and immersed in formalin buffer. Territory fibrosis was studied and scored in the renal medulla using Azan staining.

RESULTS

Fibrosis area scores (means ± standard deviations) based on Azan staining were 1.00 ± 0.46 in the control group, 2.85 ± 0.93 in the HI-NT group, and 3.58 ± 1.14 in the HI-TH group. The fibrosis area of the HI-NT and HI-TH groups was larger than that of the control. The HI-NT and HI-TH groups were not statistically different.

CONCLUSIONS

Renal fibrosis is affected by perinatal asphyxia and cannot be prevented by TH, based on histopathological findings.

Cerebral blood volume increment after resuscitation measured by near-infrared time-resolved spectroscopy can estimate degree of hypoxic-ischemic insult in newborn piglets

Neonatal hypoxic–ischemic encephalopathy is a notable cause of neonatal death and developmental disabilities. To achieve better outcomes, it is important in treatment strategy selection to categorize the degree of hypoxia ischemia and evaluate dose response. In an asphyxia piglet model with histopathological brain injuries that we previously developed, animals survived 5 days after insult and showed changes in cerebral blood volume (CBV) that reflected the severity of injuries. However, little is known about the relationship between changes in CBV during and after insult. In this study, an HI event was induced by varying the amount and timing of inspired oxygen in 20 anesthetized piglets. CBV was measured using near-infrared time-resolved spectroscopy before, during, and 6 h after insult. Change in CBV was calculated as the difference between the peak CBV value during insult and the value at the end of insult. The decrease in CBV during insult was found to correlate with the increase in CBV within 6 h after insult. Heart rate exhibited a similar tendency to CBV, but blood pressure did not. Because the decrement in CBV was larger in severe HI, the CBV increment immediately after insult is considered useful for assessing degree of HI insult.

Non-invasive diffuse optical neuromonitoring during cardiopulmonary resuscitation predicts return of spontaneous circulation

Neurologic injury is a leading cause of morbidity and mortality following pediatric cardiac arrest. In this study, we assess the feasibility of quantitative, non-invasive, frequency-domain diffuse optical spectroscopy (FD-DOS) neuromonitoring during cardiopulmonary resuscitation (CPR), and its predictive utility for return of spontaneous circulation (ROSC) in an established pediatric swine model of cardiac arrest. Cerebral tissue optical properties, oxy- and deoxy-hemoglobin concentration ([HbO₂], [Hb]), oxygen saturation (StO₂) and total hemoglobin concentration (THC) were measured by a FD-DOS probe placed on the forehead in 1-month-old swine (8–11 kg; n = 52) during seven minutes of asphyxiation followed by twenty minutes of CPR. ROSC prediction and time-dependent performance of prediction throughout early CPR (< 10 min), were assessed by the weighted Youden index (J_w, w = 0.1) with tenfold cross-validation. FD-DOS CPR data was successfully acquired in 48/52 animals; 37/48 achieved ROSC. Changes in scattering coefficient (785 nm), [HbO₂], StO₂ and THC from baseline were significantly different in ROSC versus No-ROSC subjects (p < 0.01) after 10 min of CPR. Change in [HbO₂] of + 1.3 µmol/L from 1-min of CPR achieved the highest weighted Youden index (0.96) for ROSC prediction. We demonstrate feasibility of quantitative, non-invasive FD-DOS neuromonitoring, and stable, specific, early ROSC prediction from the third minute of CPR.

Pathophysiology of Cerebral Hyperperfusion in Term Neonates With Hypoxic-Ischemic Encephalopathy: A Systematic Review for Future Research

Worldwide neonatal hypoxic-ischemic encephalopathy (HIE) is a common cause of mortality and neurologic disability, despite the implementation of therapeutic hypothermia treatment. Advances toward new neuroprotective interventions have been limited by incomplete knowledge about secondary injurious processes such as cerebral hyperperfusion commonly observed during the first 1-5 days after asphyxia. Cerebral hyperperfusion is correlated with adverse neurodevelopmental outcome and it is a process that remains poorly understood. In order to provide an overview of the existing knowledge on the pathophysiology and highlight the gaps in current understanding of cerebral hyperperfusion in term animals and neonates with HIE, we performed a systematic research. We included papers scoping for study design, population, number of participants, study technique and relevant findings. Methodological quality was assessed using the checklist for cohort studies from The Joanna Briggs Institute. Out of 2,690 results, 34 studies were included in the final review-all prospective cohort studies. There were 14 studies of high, 17 moderate and 3 of low methodological quality. Data from the literature were analyzed in two main subjects: (1) Hemodynamic Changes subdivided into macro- and microscopic hemodynamic changes, and (2) Endogenous Pathways which was subdivided into N-methyl-D-aspartate/Mitogen activated protein kinase (NDMA/MAPK), Nitric Oxide (NO), prostanoids and other endogenous studies. Cerebral hyperperfusion in term neonates with HIE was found to be present 10-30 min after the hypoxic-ischemic event and was still present around day 10 and up to 1 month after birth. Cerebral hyperperfusion was also characterized by angiogenesis and cerebral vasodilation. Additionally, cerebral vasodilation was mediated by endogenous pathways such as MAPK through urokinase Plasminogen Activator (uPA), by neuronal NO synthase following NMDA and by prostanoid synthesis. Future research should elucidate the precise role of NMDA, MAPK and prostanoids in cerebral hyperperfusion. Moreover, research should focus on possible interventions and the effect of hypothermia on hyperperfusion. These findings should be taken into account simultaneously with brain imagining techniques, becoming a valuable asset in assessing the impact in neurodevelopmental outcome.

Hydrogen ventilation combined with mild hypothermia improves short-term neurological outcomes in a 5-day neonatal hypoxia-ischaemia piglet model

Despite its poor outcomes, therapeutic hypothermia (TH) is the current standard treatment for neonatal hypoxic-ischaemic encephalopathy (HIE). In this study, due to its antioxidant, anti-inflammatory, and antiapoptotic properties, the effectiveness of molecular hydrogen (H₂) combined with TH was evaluated by means of neurological and histological assessments. Piglets were divided into three groups: hypoxic-ischaemic insult with normothermia (NT), insult with hypothermia (TH, 33.5 ± 0.5 °C), and insult with hypothermia with H₂ ventilation (TH-H₂, 2.1–2.7%). H₂ ventilation and TH were administered for 24 h. After ventilator weaning, neurological assessment was performed every 6 h for 5 days. On day 5, the brains of the piglets were harvested for histopathological analysis. Regarding the neurological score, the piglets in the TH-H₂ group consistently had the highest score from day 2 to 5 and showed a significantly higher neurological score from day 3 compared with the NT group. Most piglets in the TH-H₂ group could walk at day 3 of recovery, whereas walking ability was delayed in the two other groups. The histological results revealed that TH-H₂ tended to improve the status of cortical gray matter and subcortical white matter, with a considerable reduction in cell death. In this study, the combination of TH and H₂ improved short-term neurological outcomes in neonatal hypoxic-ischaemic piglets.

Relationship between prolonged neural suppression and cerebral hemodynamic dysfunction during hypothermia in asphyxiated piglets

OBJECTIVES

Hypothermia (HT) improves the outcome of neonatal hypoxic-ischemic encephalopathy. Here, we investigated changes during HT in cortical electrical activity using amplitude-integrated electroencephalography (aEEG) and in cerebral blood volume (CBV) and cerebral hemoglobin oxygen saturation using near-infrared time-resolved spectroscopy (TRS) and compared the results with those obtained during normothermia (NT) after a hypoxic-ischemic (HI) insult in a piglet model of asphyxia. We previously reported that a greater increase in CBV can indicate greater pressure-passive cerebral perfusion due to more severe brain injury and correlates with prolonged neural suppression during NT. We hypothesized that when energy metabolism is suppressed during HT, the cerebral hemodynamics of brains with severe injury would be suppressed to a greater extent, resulting in a greater decrease in CBV during HT that would correlate with prolonged neural suppression after insult.

METHODS

Twenty-six piglets were divided into four groups: control with NT (C-NT, n = 3), control with HT (C-HT, n = 3), HI insult with NT (HI-NT, n = 10), and HI insult with HT (HI-HT, n = 10). TRS and aEEG were performed in all groups until 24 h after the insult. Piglets in the HI-HT group were maintained in a hypothermic state for 24 h after the insult.

RESULTS

There was a positive linear correlation between changes in CBV at 1, 3, 6, and 12 h after the insult and low-amplitude aEEG (<5 µV) duration after insult in the HI-NT group, but a negative linear correlation between these two parameters at 6 and 12 h after the insult in the HI-HT group. The aEEG background score and low-amplitude EEG duration after the insult did not differ between these two groups.

DISCUSSION AND CONCLUSION

A longer low-amplitude EEG duration after insult was associated with a greater CBV decrease during HT in the HI-HT group, suggesting that brains with more severe neural suppression could be more prone to HT-induced suppression of cerebral metabolism and circulation.

Hypoxic-Ischemic Encephalopathy-Associated Liver Fatty Degeneration and the Effects of Therapeutic Hypothermia in Newborn Piglets

BACKGROUND

Although liver can be injured under the hypoxic-ischemic encephalopathy (HIE) condition, there is currently no histopathological evidence. Therapeutic hypothermia is used to protect the brain; however, the therapeutic potential for concomitant liver injury is unknown.

OBJECTIVES

This study aimed to histopathologically prove HIE-associated liver injury and to investigate the influence of therapeutic hypothermia in a newborn piglet HIE model.

METHODS

Eighteen newborn piglets were divided into 3 groups: control (n = 4), HIE (n = 8), and therapeutic hypothermia (n = 6) groups. The hypoxic insult was induced by decreasing the fraction of inspiratory oxygen from 21 to 2-4% over 40 min while monitoring cerebral blood volume and cerebral hemoglobin oxygen saturation. For therapeutic hypothermia, whole-body cooling at 33-34°C was administered for 24 h after the hypoxic insult. We hematologically and histopathologically investigated the liver injury in all groups.

RESULTS

Alanine transaminase and lactate dehydrogenase levels in the HIE group were significantly elevated compared with those in the control group. Micro-lipid droplet accumulation in the periportal zone, but not in the perivenous zone, was significantly greater in the HIE group than in the control group and significantly smaller in the therapeutic hypothermia group than in the HIE group.

CONCLUSIONS

We demonstrated that micro-lipid droplet accumulation in the cytoplasm of hepatocytes in the periportal zone occurs under the HIE condition and that this accumulation is suppressed by therapeutic hypothermia.