Relationships between cerebral autoregulation and markers of kidney and liver injury in neonatal encephalopathy and therapeutic hypothermia

Hypothermic Protection in Neocortex Is Topographic and Laminar, Seizure Unmitigating, and Partially Rescues Neurons Depleted of RNA Splicing Protein Rbfox3/NeuN in Neonatal Hypoxic-Ischemic Male Piglets

The effects of hypothermia on neonatal encephalopathy may vary topographically and cytopathologically in the neocortex with manifestations potentially influenced by seizures that alter the severity, distribution, and type of neuropathology. We developed a neonatal piglet survival model of hypoxic-ischemic (HI) encephalopathy and hypothermia (HT) with continuous electroencephalography (cEEG) for seizures. Neonatal male piglets received HI-normothermia (NT), HI-HT, sham-NT, or sham-HT treatments. Randomized unmedicated sham and HI piglets underwent cEEG during recovery. Survival was 2-7 days. Normal and pathological neurons were counted in different neocortical areas, identified by cytoarchitecture and connectomics, using hematoxylin and eosin staining and immunohistochemistry for RNA-binding FOX-1 homolog 3 (Rbfox3/NeuN). Seizure burden was determined. HI-NT piglets had a reduced normal/total neuron ratio and increased ischemic-necrotic/total neuron ratio relative to sham-NT and sham-HT piglets with differing severities in the anterior and posterior motor, somatosensory, and frontal cortices. Neocortical neuropathology was attenuated by HT. HT protection was prominent in layer III of the inferior parietal cortex. Rbfox3 immunoreactivity distinguished cortical neurons as: Rbfox3-positive/normal, Rbfox3-positive/ischemic-necrotic, and Rbfox3-depleted. HI piglets had an increased Rbfox3-depleted/total neuron ratio in layers II and III compared to sham-NT piglets. Neuronal Rbfox3 depletion was partly rescued by HT. Seizure burdens in HI-NT and HI-HT piglets were similar. We conclude that the neonatal HI piglet neocortex has: (1) suprasylvian vulnerability to HI and seizures; (2) a limited neuronal cytopathological repertoire in functionally different regions that engages protective mechanisms with HT; (3) higher seizure burden, insensitive to HT, that is correlated with more panlaminar ischemic-necrotic neurons in the somatosensory cortex; and (4) pathological RNA splicing protein nuclear depletion that is sensitive to HT. This work demonstrates that HT protection of the neocortex in neonatal HI is topographic and laminar, seizure unmitigating, and restores neuronal depletion of RNA splicing factor.

Creatinine Trends and Patterns in Neonates Undergoing Whole Body Hypothermia: A Systematic Review

Many neonates undergoing whole body hypothermia (WBH) following moderate to severe perinatal asphyxia may also suffer from renal impairment. While recent data suggest WBH-related reno-protection, differences in serum creatinine (Scr) patterns to reference patterns were not yet reported. We therefore aimed to document Scr trends and patterns in asphyxiated neonates undergoing WBH and compared these to centiles from a reference Scr data set of non-asphyxiated (near)term neonates. Using a systematic review strategy, reports on Scr trends (mean ± SD, median or interquartile range) were collected (day 1-7) in WBH cohorts and compared to centiles of an earlier reported reference cohort of non-asphyxia cases. Based on 13 papers on asphyxia + WBH cases, a pattern of postnatal Scr trends in asphyxia + WBH cases was constructed. Compared to the reference 50th centile Scr values, mean or median Scr values at birth and up to 48 h were higher in asphyxia + WBH cases with a subsequent uncertain declining trend towards, at best, high or high-normal creatinine values afterwards. Such patterns are valuable for anticipating average changes in renal drug clearance but do not yet cover the relevant inter-patient variability observed in WBH cases, as this needs pooling of individual Screa profiles, preferably beyond the first week of life.

Wavelet Autoregulation Monitoring Identifies Blood Pressures Associated With Brain Injury in Neonatal Hypoxic-Ischemic Encephalopathy

Dysfunctional cerebrovascular autoregulation may contribute to neurologic injury in neonatal hypoxic-ischemic encephalopathy (HIE). Identifying the optimal mean arterial blood pressure (MAPopt) that best supports autoregulation could help identify hemodynamic goals that support neurologic recovery. In neonates who received therapeutic hypothermia for HIE, we hypothesized that the wavelet hemoglobin volume index (wHVx) would identify MAPopt and that blood pressures closer to MAPopt would be associated with less brain injury on MRI. We also tested a correlation-derived hemoglobin volume index (HVx) and single- and multi-window data processing methodology. Autoregulation was monitored in consecutive 3-h periods using near infrared spectroscopy in an observational study. The neonates had a mean MAP of 54 mmHg (standard deviation: 9) during hypothermia. Greater blood pressure above the MAPopt from single-window wHVx was associated with less injury in the paracentral gyri (p = 0.044; n = 63), basal ganglia (p = 0.015), thalamus (p = 0.013), and brainstem (p = 0.041) after adjustments for sex, vasopressor use, seizures, arterial carbon dioxide level, and a perinatal insult score. Blood pressure exceeding MAPopt from the multi-window, correlation HVx was associated with less injury in the brainstem (p = 0.021) but not in other brain regions. We conclude that applying wavelet methodology to short autoregulation monitoring periods may improve the identification of MAPopt values that are associated with brain injury. Having blood pressure above MAPopt with an upper MAP of ~50–60 mmHg may reduce the risk of brain injury during therapeutic hypothermia. Though a cause-and-effect relationship cannot be inferred, the data support the need for randomized studies of autoregulation and brain injury in neonates with HIE.

Later cooling within 6 h and temperatures outside 33-34 °C are not associated with dysfunctional autoregulation during hypothermia for neonatal encephalopathy

BACKGROUND

Cooling delays, temperature outside 33-34 °C, and blood pressure below the mean arterial blood pressure with optimal cerebral autoregulation (MAP_OPT) might diminish neuroprotection from therapeutic hypothermia in neonates with hypoxic-ischemic encephalopathy (HIE). We hypothesized that longer time to reach temperature <34 °C and having temperature outside 33-34 °C would be associated with worse autoregulation and greater brain injury.

METHODS

Neonates with HIE had rectal temperature and near-infrared spectroscopy autoregulation monitoring during hypothermia (n = 63) and rewarming (n = 58). All underwent brain MRI, and a subset received diffusion tensor imaging MRI before day 10 (n = 41).

RESULTS

Most neonates reached <34 °C at 3-6 h of life. MAP_OPT was identified in 54/63 (86%) during hypothermia and in 53/58 (91%) during rewarming. Cooling time was not related to blood pressure deviation from MAP_OPT. Later cooling was associated with lower ADC scalar in unilateral posterior centrum semiovale but not in other regions. Temperatures >34 °C were associated with blood pressure above MAP_OPT but not with brain injury.

CONCLUSIONS

In neonates who were predominantly cooled after 3 h, cooling time was not associated with autoregulation or overall brain injury. Blood pressure deviation above MAP_OPT was associated with temperature >34 °C. Additional studies are needed in a more heterogeneous population.

IMPACT

Cooling time to reach target hypothermia temperature within 6 h of birth did not affect cerebral autoregulation measured by NIRS in neonates with hypoxic-ischemic encephalopathy (HIE). Temperature fluctuations >33-34 °C were associated with blood pressures that exceeded the range of optimal autoregulatory vasoreactivity. Cooling time within 6 h of birth and temperatures >33-34 °C were not associated with qualitative brain injury on MRI. Regional apparent diffusion coefficient scalars on diffusion tensor imaging MRI were not appreciably affected by cooling time or temperature >33-34 °C. Additional research in a larger and more heterogeneous population is needed to determine how delayed cooling and temperatures beyond the target hypothermia range affect autoregulation and brain injury.

Plasma vasopressin levels are closely associated with fetal hypotension and neuronal injury after hypoxia-ischemia in near-term fetal sheep

BACKGROUND

Sensitive biomarkers are needed to rapidly identify high-risk infants after hypoxia-ischemia for neuroprotective treatment. Hypotension is a key determinant of hypoxic-ischemic neural injury, and a potent stimulus of humoral pressors including angiotensin-II and arginine vasopressin. We therefore aimed to quantify the relationship between vasopressin and angiotensin-II levels in the latent phase after hypoxia-ischemia induced by umbilical cord occlusion (UCO) with both the severity of preceding hypotension and subsequent neuronal injury.

METHODS

Chronically instrumented near-term fetal sheep underwent sham-UCO or UCO for either 15 min or until mean arterial pressure was <8 mmHg. Neuronal injury was assessed after 72 h recovery.

RESULTS

Umbilical cord occlusion was associated with severe hypotension that recovered after UCO; two fetuses developed profound secondary hypotension within 6 h and died. Vasopressin levels but not angiotensin-II were significantly elevated 1-3 h after UCO and were closely associated with the severity of hypotension during UCO and the subsequent severity of neuronal loss in the parasagittal and lateral cortex, caudate nucleus and putamen. The Youden cut-point for vasopressin at 1 h was 180.0 pmol/L, with sensitivity 100% and specificity 92.3% for severe neuronal injury or death.

CONCLUSION

Vasopressin levels shortly after moderate-severe hypoxia-ischemia may be a useful early biomarker to guide the timely implementation of neuroprotective treatment.

IMPACT

It can be difficuIt to rapidly identify infants who might benefit from therapeutic hypothermia. We investigated whether increases in plasma pressor hormones early after hypoxia-ischemia were biomarkers for neonatal hypoxic-ischemic encephalopathy using near-term fetal sheep. Arginine vasopressin levels were elevated at 1-3 h after hypoxia-ischemia and were predictive of the severity of preceding hypotension and subsequent risk of severe neuronal injury or death after hypoxia-ischemia. Arginine vasopressin may help identify neonates at high risk of hypoxic-ischemic encephalopathy early within the therapeutic window for hypothermia.

Head Ultrasound Resistive Indices Are Associated With Brain Injury on Diffusion Tensor Imaging Magnetic Resonance Imaging in Neonates With Hypoxic-Ischemic Encephalopathy

BACKGROUND

Neonatal hypoxic-ischemic encephalopathy (HIE) is associated with dysfunctional cerebral autoregulation. Resistive index (RI) measured in the anterior cerebral artery on transfontanellar head ultrasound is a noninvasive measure of blood flow and may indicate autoregulation dysfunction. We tested whether RI was associated with brain injury on diffusion tensor imaging magnetic resonance imaging (MRI).

MATERIALS AND METHODS

Seventy-five neonates who underwent therapeutic hypothermia for HIE were enrolled. Resistive index values were obtained from head ultrasound performed at the end of therapeutic hypothermia. Apparent diffusion coefficient scalars were measured on MRIs performed before day of life 10.

RESULTS

Lower RI was associated with lower apparent diffusion coefficient in the centrum semiovale, basal ganglia, thalamus, and posterior limb of the internal capsule. Combining RI and Apgar scores improved the ability to distinguish injury severity on MRI relative to either metric alone.

CONCLUSIONS

Low RI correlated with worse brain injury on diffusion tensor imaging and may serve as an early marker of brain injury in cooled HIE neonates.

Assessment of cerebral autoregulation indices - a modelling perspective

Various methodologies to assess cerebral autoregulation (CA) have been developed, including model - based methods (e.g. autoregulation index, ARI), correlation coefficient - based methods (e.g. mean flow index, Mx), and frequency domain - based methods (e.g. transfer function analysis, TF). Our understanding of relationships among CA indices remains limited, partly due to disagreement of different studies by using real physiological signals, which introduce confounding factors. The influence of exogenous noise on CA parameters needs further investigation. Using a set of artificial cerebral blood flow velocities (CBFV) generated from a well-known CA model, this study aims to cross-validate the relationship among CA indices in a more controlled environment. Real arterial blood pressure (ABP) measurements from 34 traumatic brain injury patients were applied to create artificial CBFVs. Each ABP recording was used to create 10 CBFVs corresponding to 10 CA levels (ARI from 0 to 9). Mx, TF phase, gain and coherence in low frequency (LF) and very low frequency (VLF) were calculated. The influence of exogenous noise was investigated by adding three levels of colored noise to the artificial CBFVs. The result showed a significant negative relationship between Mx and ARI (r = −0.95, p < 0.001), and it became almost purely linear when ARI is between 3 to 6. For transfer function parameters, ARI positively related with phase (r = 0.99 at VLF and 0.93 at LF, p < 0.001) and negatively related with gain_VLF(r = −0.98, p < 0.001). Exogenous noise changed the actual values of the CA parameters and increased the standard deviation. Our results show that different methods can lead to poor correlation between some of the autoregulation parameters even under well controlled situations, undisturbed by unknown confounding factors. They also highlighted the importance of exogenous noise, showing that even the same CA value might correspond to different CA levels under different ‘noise’ conditions.

The Johns Hopkins Neurosciences Intensive Care Nursery Tenth Anniversary (2009-2019): A Historical Reflection and Vision for the Future

Since 2009, the Neurosciences Intensive Care Nursery at Johns Hopkins Children’s Center has provided a multidisciplinary approach toward the care of newborns with neurological disorders. The program’s cornerstone is an interdisciplinary approach that involves the primary neonatology team plus experts from more than 10 specialties who convene at a weekly team conference at which newborns with neurological problems are discussed in detail. This interdisciplinary approach fosters in-depth discussion of clinical issues to optimize the management of neonates with neurological problems as well as the opportunity to generate research ideas and provide education about neonatal neuroscience at all levels (faculty, nurses, and trainees). The purpose of this article is to provide a 10-year reflection of our Neurosciences Intensive Care Nursery with a view toward expanding efforts in the 3 areas of our mission: clinical care, research, and education. We hope that our experience will enhance the spread of neonatal neuroscience education, care, and research as widely as possible.

Neonatal cerebrovascular autoregulation

Cerebrovascular pressure autoregulation is the physiologic mechanism that holds cerebral blood flow (CBF) relatively constant across changes in cerebral perfusion pressure (CPP). Cerebral vasoreactivity refers to the vasoconstriction and vasodilation that occur during fluctuations in arterial blood pressure (ABP) to maintain autoregulation. These are vital protective mechanisms of the brain. Impairments in pressure autoregulation increase the risk of brain injury and persistent neurologic disability. Autoregulation may be impaired during various neonatal disease states including prematurity, hypoxic-ischemic encephalopathy (HIE), intraventricular hemorrhage, congenital cardiac disease, and infants requiring extracorporeal membrane oxygenation (ECMO). Because infants are exquisitely sensitive to changes in cerebral blood flow (CBF), both hypoperfusion and hyperperfusion can cause significant neurologic injury. We will review neonatal pressure autoregulation and autoregulation monitoring techniques with a focus on brain protection. Current clinical therapies have failed to fully prevent permanent brain injuries in neonates. Adjuvant treatments that support and optimize autoregulation may improve neurologic outcomes.

Renal Saturation and Acute Kidney Injury in Neonates with Hypoxic Ischemic Encephalopathy Undergoing Therapeutic Hypothermia

OBJECTIVE

To investigate the range of renal near-infrared spectroscopy (NIRS) measures in neonates undergoing therapeutic hypothermia for hypoxic ischemic encephalopathy (HIE) and to determine the association between renal NIRS measures and the development of acute kidney injury (AKI).

STUDY DESIGN

A retrospective chart review was conducted of neonates with moderate to severe HIE who received therapeutic hypothermia at a tertiary care center from 2014 to 2016. Neonates had routine continuous NIRS monitoring of cerebral and renal saturation (Rsat) as part of their clinical care for 72 hours of cooling and until 24 hours after rewarming. The outcome of AKI was defined by an abnormal rate of decline of serum creatinine over the first 5 days of life. Mixed effects models determined the association between renal NIRS measures and AKI over time.

RESULTS

Of 38 neonates with HIE undergoing cooling, 15 (39%) developed AKI. Rsat was lower than cerebral saturation during cooling (P < .01), but Rsat increased over time after rewarming, while renal oxygen extraction levels decreased (P < .0001). Neonates with AKI had higher Rsat levels (P < .01) compared with those without AKI after 24 hours of life. Using receiver operating characteristic curves, Rsat >75% by 24-48 hours predicted AKI with a sensitivity of 79% and specificity of 82% (area under the receiver operating characteristic curve = 0.76).

CONCLUSIONS

Throughout cooling, neonates with AKI had higher Rsat measures than those without AKI. These differences may reflect lower oxygen extraction by the injured kidney. NIRS monitoring of Rsat may identify neonates with HIE at risk of developing AKI.

Utility of prenatal Doppler ultrasound to predict neonatal impaired cerebral autoregulation

OBJECTIVE

Determine if abnormal prenatal Doppler ultrasound indices are predictive of postnatal impaired cerebral autoregulation.

STUDY DESIGN

Prospective cohort study of 46 subjects, 24⁰-29⁶ weeks' gestation. Utilizing near-infrared spectroscopy and receiver-operating characteristic analysis, impaired cerebral autoregulation was defined as >16.5% time spent in a dysregulated state within 96 h of life. Normal and abnormal Doppler indices were compared for perinatal outcomes.

RESULTS

Subjects with abnormal cerebroplacental ratio (n = 12) and abnormal umbilical artery pulsatility index (n = 13) were likely to develop postnatal impaired cerebral autoregulation (p ≤ 0.02). Abnormal cerebroplacental ratio was associated with impaired cerebral autoregulation between 24 and 48 h of life (p = 0.016). These subjects have increased risk for fetal growth restriction, lower birth weight, lower Apgar scores, acidosis, and severe intraventricular hemorrhage and/or death (p < 0.05).

CONCLUSION

Abnormal cerebroplacental ratio and umbilical artery pulsatility index are associated with postnatal impairment in cerebral autoregulation and adverse outcome.