Recooling for rebound seizures after rewarming in neonatal encephalopathy

Reverse Therapy: Impact of Hyperthermia and Rewarming on Newborn Outcomes

Therapeutic hypothermia is now well established to improve neurodevelopmental outcomes after hypoxic-ischemic encephalopathy (HIE). Although the overall principles of treatment are now well established, many smaller questions are unclear. The potential impact of reversal of hypothermia therapy and the effect of high temperatures on recovery of the neurovascular unit after therapeutic hypothermia for HIE has received relatively little attention. This article will address the effects of hypoxia-ischemia and rewarming and increased temperatures on the neurovascular unit in preclinical and clinical models.

Diabetes drugs activate neuroprotective pathways in models of neonatal hypoxic-ischemic encephalopathy

Hypoxic-ischaemic encephalopathy (HIE) arises from diminished blood flow and oxygen to the neonatal brain during labor, leading to infant mortality or severe brain damage, with a global incidence of 1.5 per 1000 live births. Glucagon-like Peptide 1 Receptor (GLP1-R) agonists, used in type 2 diabetes treatment, exhibit neuroprotective effects in various brain injury models, including HIE. In this study, we observed enhanced neurological outcomes in post-natal day 10 mice with surgically induced hypoxic-ischaemic (HI) brain injury after immediate systemic administration of exendin-4 or semaglutide. Short- and long-term assessments revealed improved neuropathology, survival rates, and locomotor function. We explored the mechanisms by which GLP1-R agonists trigger neuroprotection and reduce inflammation following oxygen-glucose deprivation and HI in neonatal mice, highlighting the upregulation of the PI3/AKT signalling pathway and increased cAMP levels. These findings shed light on the neuroprotective and anti-inflammatory effects of GLP1-R agonists in HIE, potentially extending to other neurological conditions, supporting their potential clinical use in treating infants with HIE.

Seizures after initiation of rewarming in cooled infants with hypoxic ischaemic encephalopathy

BACKGROUND

Seizures after initiation of rewarming from therapeutic hypothermia for neonatal encephalopathy are well recognised but not easy to predict.

METHODS

A secondary analysis was performed of NEOLEV2 trial data, a multicentre randomised trial of levetiracetam versus phenobarbital for neonatal seizures. Enrolled infants underwent continuous video EEG (cEEG) monitoring. The trial data were reviewed for 42 infants with seizures during therapeutic hypothermia and 118 infants who received therapeutic hypothermia but had no seizures on cEEG.

RESULTS

Overall, 112 of 160 (70%) had cEEG monitoring continued until rewarming was completed. Of the 42 infants with prior seizures, there were 30 infants with valid cEEG available and seizures occurred following the initiation of rewarming in 8 (26.6%). For the 118 seizure-naive infants, 82 (69.5%) continued cEEG until either rewarming was completed or 90 h of age and none had documented seizures.

CONCLUSION

Overall, just over a quarter of infants with prior seizures had cEEG evidence of at least one seizure in the 24 h after initiation of rewarming but no seizure-naive infant had cEEG evidence of seizure(s) on rewarming. Critically, by reporting the two groups separately, the data can provide guidance on the duration of EEG monitoring.

IMPACT

Infants with hypoxic ischaemic encephalopathy who have cEEG evidence of seizures during therapeutic hypothermia have a significant risk of further seizures on rewarming. For infants with hypoxic ischaemic encephalopathy but no cEEG evidence of seizures during therapeutic hypothermia, there is very little risk of de novo seizures. Ongoing work utilising large cohorts may generate EEG criteria that refine estimates of risk for rewarming seizures. Based on current experience, if seizures have occurred during therapeutic hypothermia for hypoxic ischaemic encephalopathy, the EEG monitoring should be continued during rewarming and for 12 h thereafter to minimise the risk of missing an event.

Advances in Therapies to Treat Neonatal Hypoxic-Ischemic Encephalopathy

Neonatal hypoxic-ischemic encephalopathy (HIE) is a condition that results in brain damage in newborns due to insufficient blood and oxygen supply during or after birth. HIE is a major cause of neurological disability and mortality in newborns, with over one million neonatal deaths occurring annually worldwide. The severity of brain injury and the outcome of HIE depend on several factors, including the cause of oxygen deprivation, brain maturity, regional blood flow, and maternal health conditions. HIE is classified into mild, moderate, and severe categories based on the extent of brain damage and resulting neurological issues. The pathophysiology of HIE involves different phases, including the primary phase, latent phase, secondary phase, and tertiary phase. The primary and secondary phases are characterized by episodes of energy and cell metabolism failures, increased cytotoxicity and apoptosis, and activated microglia and inflammation in the brain. A tertiary phase occurs if the brain injury persists, characterized by reduced neural plasticity and neuronal loss. Understanding the cellular and molecular aspects of the different phases of HIE is crucial for developing new interventions and therapeutics. This review aims to discuss the pathophysiology of HIE, therapeutic hypothermia (TH), the only approved therapy for HIE, ongoing developments of adjuvants for TH, and potential future drugs for HIE.

[Clinical efficacy of mild therapeutic hypothermia with different rewarming time on neonatal hypoxic-ischemic encephalopathy: a prospective randomized controlled study]

OBJECTIVES

To investigate the clinical efficacy of mild therapeutic hypothermia (MTH) with different rewarming time on neonatal hypoxic-ischemic encephalopathy (HIE).

METHODS

A prospective study was performed on 101 neonates with HIE who were born and received MTH in Zhongshan Hospital, Xiamen University, from January 2018 to January 2022. These neonates were randomly divided into two groups: MTH1 group (n=50; rewarming for 10 hours at a rate of 0.25°C/h) and MTH2 group (n=51; rewarming for 25 hours at a rate of 0.10°C/h). The clinical features and the clinical efficacy were compared between the two groups. A binary logistic regression analysis was used to identify the factors influencing the occurrence of normal sleep-wake cycle (SWC) on amplitude-integrated electroencephalogram (aEEG) at 25 hours of rewarming.

RESULTS

There were no significant differences between the MTH1 and MTH2 groups in gestational age, 5-minute Apgar score, and proportion of neonates with moderate/severe HIE (P>0.05). Compared with the MTH2 group, the MTH1 group tended to have a normal arterial blood pH value at the end of rewarming, a significantly shorter duration of oxygen dependence, a significantly higher proportion of neonates with normal SWC on aEEG at 10 and 25 hours of rewarming, and a significantly higher Neonatal Behavioral Neurological Assessment score on days 5, 12, and 28 after birth (P<0.05), while there was no significant difference in the incidence rate of rewarming-related seizures between the two groups (P>0.05). There were no significant differences between the two groups in the incidence rate of neurological disability at 6 months of age and the score of Bayley Scale of Infant Development at 3 and 6 months of age (P>0.05). The binary logistic regression analysis showed that prolonged rewarming time (25 hours) was not conducive to the occurrence of normal SWC (OR=3.423, 95%CI: 1.237-9.469, P=0.018).

CONCLUSIONS

Rewarming for 10 hours has a better short-term clinical efficacy than rewarming for 25 hours. Prolonging rewarming time has limited clinical benefits on neonates with moderate/severe HIE and is not conducive to the occurrence of normal SWC, and therefore, it is not recommended as a routine treatment method.

Process variations between Swiss units treating neonates with hypoxic-ischemic encephalopathy and their effect on short-term outcome

OBJECTIVE

To compare therapeutic hypothermia (TH) treatment of term and near-term neonates with hypoxic-ischemic encephalopathy (HIE) between neonatal units.

STUDY DESIGN

Population-based, retrospective analysis of TH initiation and maintenance, and of diagnostic imaging. The comparison between units was based on crude data analysis, indirect standardization, and adjusted logistic regression.

RESULTS

TH was provided to 570 neonates with HIE between 2011 and 2018 in 10 Swiss units. We excluded 121 off-protocol cooled neonates to avoid selection bias. Of the remaining 449 neonates, the outcome was favorable to international benchmarks, but there were large unit-to-unit variations in baseline perinatal data and TH management. A total of 5% neonates did not reach target temperature within 7 h (3-10% between units), and 29% experienced over- or undercooling (0-38%).

CONCLUSION

Although the neonates had favorable short-term outcomes, areas for improvement remain for Swiss units in both process and outcome measures.

Association Between Increased Seizures During Rewarming After Hypothermia for Neonatal Hypoxic Ischemic Encephalopathy and Abnormal Neurodevelopmental Outcomes at 2-Year Follow-up: A Nested Multisite Cohort Study

Importance

Compared with normothermia, hypothermia has been shown to reduce death or disability in neonatal hypoxic ischemic encephalopathy but data on seizures during rewarming and associated outcomes are scarce.

Objective

To determine whether electrographic seizures are more likely to occur during rewarming compared with the preceding period and whether they are associated with abnormal outcomes in asphyxiated neonates receiving hypothermia therapy.

Design, Setting, and Participants

This prespecified nested cohort study of infants enrolled in the Optimizing Cooling (OC) multicenter Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) Neonatal Research Network trial from December 2011 to December 2013 with 2 years' follow-up randomized infants to either 72 hours of cooling (group A) or 120 hours (group B). The main trial included 364 infants. Of these, 194 were screened, 10 declined consent, and 120 met all predefined inclusion criteria. A total of 112 (90%) had complete data for death or disability. Data were analyzed from January 2018 to January 2020.

Interventions

Serial amplitude electroencephalography recordings were compared in the 12 hours prior and 12 hours during rewarming for evidence of electrographic seizure activity by 2 central amplitude-integrated electroencephalography readers blinded to treatment arm and rewarming epoch. Odds ratios and 95% CIs were evaluated following adjustment for center, prior seizures, depth of cooling, and encephalopathy severity.

Main Outcomes and Measures

The primary outcome was the occurrence of electrographic seizures during rewarming initiated at 72 or 120 hours compared with the preceding 12-hour epoch. Secondary outcomes included death or moderate or severe disability at age 18 to 22 months. The hypothesis was that seizures during rewarming were associated with higher odds of abnormal neurodevelopmental outcomes.

Results

A total of 120 newborns (70 male [58%]) were enrolled (66 in group A and 54 in group B). The mean (SD) gestational age was 39 (1) weeks. There was excellent interrater agreement (κ, 0.99) in detection of seizures. More infants had electrographic seizures during the rewarming epoch compared with the preceding epoch (group A, 27% vs 14%; P = .001; group B, 21% vs 10%; P = .03). Adjusted odd ratios (95% CIs) for seizure frequency during rewarming were 2.7 (1.0-7.5) for group A and 3.2 (0.9-11.6) for group B. The composite death or moderate to severe disability outcome at 2 years was significantly higher in infants with electrographic seizures during rewarming (relative risk [95% CI], 1.7 [1.25-2.37]) after adjusting for baseline clinical encephalopathy and seizures as well as center.

Conclusions and Relevance

Findings that higher odds of electrographic seizures during rewarming are associated with death or disability at 2 years highlight the necessity of electroencephalography monitoring during rewarming in infants at risk.

Trial Registration

ClinicalTrials.gov Identifier: NCT01192776.

Seizures severity during rewarming can predict seizure outcomes of infants with neonatal hypoxic-ischemic encephalopathy following therapeutic hypothermia

Background

The aim of this study was to examine the predictive value of amplitude-integrated electroencephalography (aEEG) on 12-month seizure outcomes of infants with neonatal hypoxic-ischemic encephalopathy (HIE) treated with therapeutic hypothermia.

Methods

We conducted this retrospective cohort study in a tertiary neonatal intensive care unit between May 2012 and September 2017. Neonates with HIE who received both therapeutic hypothermia (TH) and aEEG were enrolled.

Results

A total of 23 infants (14 boys, nine girls) with a mean gestational age of 38.9 weeks were enrolled. Fifteen (65%) infants had moderate HIE and eight (35%) had severe HIE according to modified Sarnat staging. The mean aEEG recording time was 107.5 h. Twenty (86.9%) infants had seizure activity during the first 24 h after cooling and 14 (60.8%) had seizure activity during the first 24 h after rewarming. At 12 months, five (21.7%) infants had poor seizure outcomes. Repetitive seizures or status epilepticus pattern during the first 24 h after rewarming, but not the first 24 h after cooling, were associated with the presence of epilepsy at 12 months (p = 0.037).

Conclusions

We identified a high incidence of electrographic seizures in infants with neonatal HIE treated with therapeutic hypothermia, and post-neonatal epilepsy in the children who survived after HIE. Repetitive seizures or status epilepticus pattern during the first 24 h after rewarming, but not in the first 24 h after cooling, were associated with the presence of epilepsy at 12 months.

Changes in Brain Tissue Oxygenation and Metabolism During Rewarming After Neonatal Encephalopathy are Related to Electrical Abnormality

Hypoxic ischemic encephalopathy (HIE) leads to significant mortality and morbidity, and therapeutic hypothermia (TH) has become a standard of care following HIE. After TH, the body temperature is brought back to 37 °C. Early electroencephalography (EEG) is a reliable outcome biomarker following HIE. We hypothesized that changes in cerebral oxidative metabolism, measured as Δ[oxCCO], in relation to changes in brain tissue oxygenation (measured as Δ[HbD]) during rewarming will correlate with injury severity as evidenced on amplitude integrated EEG/EEG at initial presentation. Broadband near-infrared spectroscopy (NIRS) and systemic data were collected during rewarming from 14 infants following HIE over a mean period of 12.5 h. All infants were monitored with video EEG telemetry using a standard neonatal montage. aEEG and EEG background was classified into mild, moderate and severely abnormal groups based on the background pattern. Two infants had mild, 6 infants had moderate and another 6 infants had severe abnormality at presentation. The relationship between [oxCCO] and [HbD] was evaluated between two groups of infants with abnormal electrical activity (mild vs moderate to severe). A significant difference was noted between the groups in the relationship between [oxCCO] and [HbD] (as r²) (p = 0.02). This result indicates that the mitochondrial injury and deranged oxidative metabolism persists in the moderate to severely abnormal group during rewarming.

The probability of seizures during continuous EEG monitoring in high-risk neonates

OBJECTIVE

We evaluated the impact of monitoring indication, early electroencephalography (EEG), and clinical features on seizure risk in all neonates undergoing continuous EEG (cEEG) monitoring following a standardized monitoring protocol.

METHODS

All cEEGs from unique neonates 34-48 weeks postmenstrual age monitored from 1/2011-10/2017 (n = 291) were included. We evaluated the impact of cEEG monitoring indication (acute neonatal encephalopathy [ANE], suspicious clinical events [SCEs], or other high-risk conditions [OHRs]), age, medication status, and early EEG abnormalities (including the presence of epileptiform discharges and abnormal background continuity, amplitude, asymmetry, asynchrony, excessive sharp transients, and burst suppression) on time to first seizure and overall seizure risk using Kaplan-Meier survival curves and multivariable Cox proportional hazards models.

RESULTS

Seizures occurred in 28% of high-risk neonates. Discontinuation of monitoring after 24 hours of seizure-freedom would have missed 8.5% of neonates with seizures. Overall seizure risk was lower in neonates monitored for ANE compared to OHR (P = .004) and trended lower compared to SCE (P = .097). The time course of seizure presentation varied by group, where the probability of future seizure was less than 1% after 17 hours of seizure-free monitoring in the SCE group, but required 42 hours in the OHR group, and 73 hours in the ANE group. The presence of early epileptiform discharges increased seizure risk in each group (ANE: adjusted hazard ratio [aHR] 4.32, 95% confidence interval [CI] 1.23-15.13, P = .022; SCE: aHR 10.95, 95% CI 4.77-25.14, P < 1e-07; OHR: aHR 56.90, 95% CI 10.32-313.72, P < 1e-05).

SIGNIFICANCE

Neonates who undergo cEEG are at high risk for seizures, and risk varies by monitoring indication and early EEG findings. Seizures are captured in nearly all neonates undergoing monitoring for SCE within 24 hours of cEEG monitoring. Neonates monitored for OHR and ANE can present with delayed seizures and require longer durations of monitoring. Early epileptiform discharges are the best early EEG feature to predict seizure risk.

Limited benefit of slow rewarming after cerebral hypothermia for global cerebral ischemia in near-term fetal sheep

The optimal rate of rewarming after therapeutic hypothermia for neonatal hypoxic-ischemic encephalopathy is unknown, although it is widely suggested that slow rewarming is beneficial. Some preclinical studies suggest better outcomes with slower rewarming, but did not control for the duration of hypothermia. In this study, near-term fetal sheep (0.85 gestation) received 30 min cerebral ischemia followed by normothermia, 48 h hypothermia with rapid rewarming over 1 h, 48-h hypothermia with slow rewarming over 24 h, or 72-h hypothermia with rapid rewarming. Slow rewarming after 48 h of hypothermia improved recovery of EEG power compared with rapid rewarming (p < 0.05), but was not different from rapid rewarming after 72 h of hypothermia. At seven days recovery, neuronal survival was partially improved by both fast and slow rewarming after 48-h hypothermia, but less than 72-h hypothermia in the cortex and CA4 (p < 0.05). In conclusion, although electrographic recovery was partially improved by slow rewarming over 24 h following cerebral hypothermia for 48 h, optimal neuroprotection was seen with hypothermia for 72 h with rapid rewarming, suggesting that the overall duration of cooling was the critical determinant of outcomes after therapeutic hypothermia.

Diagnosis of seizures and encephalopathy using conventional EEG and amplitude integrated EEG

Seizures are more common in the neonatal period than at any other time of life, partly due to the relative hyperexcitability of the neonatal brain. Brain monitoring of sick neonates in the NICU using either conventional electroencephalography or amplitude integrated EEG is essential to accurately detect seizures. Treatment of seizures is important, as evidence increasingly indicates that seizures damage the brain in addition to that caused by the underlying etiology. Prompt treatment has been shown to reduce seizure burden with the potential to ameliorate seizure-mediated damage. Neonatal encephalopathy most commonly caused by a hypoxia-ischemia results in an alteration of mental status and problems such as seizures, hypotonia, apnea, and feeding difficulties. Confirmation of encephalopathy with EEG monitoring can act as an important adjunct to other investigations and the clinical examination, particularly when considering treatment strategies such as therapeutic hypothermia. Brain monitoring also provides useful early prognostic indicators to clinicians. Recent use of machine learning in algorithms to continuously monitor the neonatal EEG, detect seizures, and grade encephalopathy offers the exciting prospect of real-time decision support in the NICU in the very near future.

Can we further optimize therapeutic hypothermia for hypoxic-ischemic encephalopathy?

Perinatal hypoxic-ischemic encephalopathy is a leading cause of neonatal death and disability. Therapeutic hypothermia significantly reduces death and major disability associated with hypoxic-ischemic encephalopathy; however, many infants still experience lifelong disabilities to movement, sensation and cognition. Clinical guidelines, based on strong clinical and preclinical evidence, recommend therapeutic hypothermia should be started within 6 hours of birth and continued for a period of 72 hours, with a target brain temperature of 33.5 ± 0.5°C for infants with moderate to severe hypoxic-ischemic encephalopathy. The clinical guidelines also recommend that infants be rewarmed at a rate of 0.5°C per hour, but this is not based on strong evidence. There are no randomized controlled trials investigating the optimal rate of rewarming after therapeutic hypothermia for infants with hypoxic-ischemic encephalopathy. Preclinical studies of rewarming are conflicting and results were confounded by treatment with sub-optimal durations of hypothermia. In this review, we evaluate the evidence for the optimal start time, duration and depth of hypothermia, and whether the rate of rewarming after treatment affects brain injury and neurological outcomes.

Predictive value of early EEG for seizures in neonates with hypoxic-ischemic encephalopathy undergoing therapeutic hypothermia

OBJECTIVES

To assess the prognostic significance of an early normal/mildly abnormal conventional EEG (cEEG) on seizure risk in neonates undergoing therapeutic hypothermia.

METHODS

We reviewed the video-EEG recordings from a large cohort of neonates treated with therapeutic hypothermia for hypoxic-ischemic encephalopathy from 2008 to 2017 in a single tertiary center. Continuous video-EEG was started as soon as possible (median 8.2 h) and continued throughout hypothermia and rewarming. We studied those neonates with a normal/mildly abnormal EEG during the first 24 h of monitoring.

RESULTS

A total of 331 neonates were treated with hypothermia and 323 had cEEG recordings available for review; 99 were excluded because of a moderately/severely abnormal cEEG background and/or seizure during the first 24 h of recording, and an additional eight because of early rewarming. The remaining 216 had a normal/mildly abnormal cEEG in the first 24 h. None of these patients subsequently developed seizures.

CONCLUSION

A normal/mildly abnormal cEEG during the first 24 h indicates a very low risk of subsequent seizures. This suggests that cEEG monitoring can be safely discontinued after 24 h if it has remained normal or excessively discontinuous and no seizures are detected, limiting the need for this resource-intensive and expensive tool.

Hypoxic-Ischemic Encephalopathy and Other Neonatal Encephalopathies

PURPOSE OF REVIEW

Neonatal encephalopathy is the most common condition in neonates encountered by child neurologists. The etiology is most often global hypoxia-ischemia due to failure of cerebral perfusion to the fetus caused by uterine, placental, or umbilical cord compromise prior to or during delivery. Other etiologies of neonatal encephalopathy include ischemic stroke and intracranial hemorrhage, infection, developmental anomalies, and inborn errors of metabolism.

RECENT FINDINGS

Therapeutic hypothermia is standard of care for the treatment of neonatal encephalopathy presumed to be caused by hypoxia-ischemia. The number needed to treat is approximately 6 to 7 to prevent one child from either death or disability at age 18 to 22 months. EEG monitoring and MRI are important tools in determining the etiology of encephalopathy and prognosis of the infant.

SUMMARY

Neonatal encephalopathy is a heterogeneous disorder that is characterized by alterations in mental status, hypotonia, seizures, and abnormalities in feeding and respiration. The most common cause of neonatal encephalopathy is hypoxic-ischemic encephalopathy, for which treatment with 72 hours of therapeutic hypothermia is associated with reduced death or disability.

Hypothermia for newborns with hypoxic-ischemic encephalopathy

Therapeutic hypothermia is a standard of care for infants ≥36 weeks gestational age (GA) with moderate-to-severe hypoxic-ischemic encephalopathy. Because some studies included infants born at 35 weeks GA, hypothermia should be considered if they meet other criteria. Cooling for infants <35 weeks GA is not recommended. Passive cooling should be started promptly in community centres, in consultation with a tertiary care centre neonatologist, while closely monitoring the infant's temperature. Best evidence suggests that maintaining core body temperature between 33°C and 34°C for 72 hours, followed by a period of rewarming of 6 to 12 hours, is optimal. Antiepileptic medications should be used when clinical or electrographic seizures are present. Maintaining serum electrolytes and glucose within normal ranges, and avoiding hypo- or hypercarbia and hyperoxia, are important adjunct treatments. A brain magnetic resonance image (MRI) is advised shortly after rewarming and, in cases where earlier findings do not match the clinical picture, a repeat MRI after 10 days of life is suggested. Multidisciplinary neurodevelopmental follow-up is recommended.

Relationship Between Cerebral Oxygenation and Metabolism During Rewarming in Newborn Infants After Therapeutic Hypothermia Following Hypoxic-Ischemic Brain Injury

Therapeutic hypothermia (TH) has become a standard of care following hypoxic ischemic encephalopathy (HIE). After TH, body temperature is brought back to 37 °C over 14 h. Lactate/N-acetylasperatate (Lac/NAA) peak area ratio on proton magnetic resonance spectroscopy ((1)H MRS) is the best available outcome biomarker following HIE. We hypothesized that broadband near infrared spectroscopy (NIRS) measured changes in the oxidation state of cytochrome-c-oxidase concentration (Δ[oxCCO]) and cerebral hemodynamics during rewarming would relate to Lac/NAA. Broadband NIRS and systemic data were collected during rewarming from 14 infants following HIE over a mean period of 12.5 h. (1)H MRS was performed on day 5-9. Heart rate increased by 20/min during rewarming while blood pressure and peripheral oxygen saturation (SpO2) remained stable. The relationship between mitochondrial metabolism and oxygenation (measured as Δ[oxCCO] and Δ[HbD], respectively) was calculated by linear regression analysis. This was reviewed in three groups: Lac/NAA values <0.5, 0.5-1, >1. Mean regression coefficient (r (2)) values in these groups were 0.41 (±0.27), 0.22 (±0.21) and 0.01, respectively. The relationship between mitochondrial metabolism and oxygenation became impaired with rising Lac/NAA. Cardiovascular parameters remained stable during rewarming.

Neuroprotective effects of deep hypothermia in refractory status epilepticus

Objective

Pharmacoresistance develops quickly during repetitive seizures, and refractory status epilepticus (RSE) remains a therapeutic challenge. The outcome of RSE is poor, with high mortality and morbidity. New treatments are needed. Deep hypothermia (20°C) is used clinically during reconstructive cardiac surgery and neurosurgery, and has proved safe and effective in those indications. We tested the hypothesis that deep hypothermia reduces RSE and its long‐term consequences.

Methods

We used a model of SE induced by lithium and pilocarpine and refractory to midazolam. Several EEG measures were recorded in both hypothermic (n = 17) and normothermic (n = 20) animals. Neuronal injury (by Fluoro‐Jade B), cell‐mediated inflammation, and breakdown of the blood–brain barrier (BBB) (by immunohistochemistry) were studied 48 h following SE onset.

Results

Normothermic rats in RSE seized for 4.1 ± 1.1 h, and at 48 h they displayed extensive neuronal injury in many brain regions, including hippocampus, dentate gyrus, amygdala, entorhinal and pyriform cortices, thalamus, caudate/putamen, and the frontoparietal neocortex. Deep hypothermia (20°C) of 30 min duration terminated RSE within 12 min of initiation of hypothermia, reduced EEG power and seizure activity upon rewarming, and eliminated SE‐induced neuronal injury in most animals. Normothermic rats showed widespread breakdown of the BBB, and extensive macrophage infiltration in areas of neuronal injury, which were completely absent in animals treated with hypothermia.

Interpretation

These results suggest that deep hypothermia may open a new therapeutic avenue for the treatment of RSE and for the prevention of its long‐term consequences.

The temporal characteristics of seizures in neonatal hypoxic ischemic encephalopathy treated with hypothermia

PURPOSE

The characteristics of electrographic seizures in newborns with hypoxic-ischaemic encephalopathy (HIE) treated with therapeutic hypothermia (TH) are poorly described. This retrospective, observational study provides reference data on the characteristics of seizures and their evolution over time in newborns with HIE receiving whole-body TH.

METHOD

The cohort under analysis included 23 infants with HIE and seizures defined by multi-channel EEG recordings. Clinical presentation, details of TH and antiepileptic drugs used were recorded. Time from first to last-recorded electrographic seizure (seizure period) was calculated. Temporal characteristics of seizures - total burden, duration, number, burden in minutes per hour, distribution of burden over time (temporal evolution), time from seizure onset to maximum seizure burden (Tmsb), T1, and time from Tmsb to seizure offset, T2 - were analysed.

RESULTS

The median age at electrographic seizure onset was 13.1h (IQR: 11.4 to 22.0). Tmsb was reached at a median age of 19.4 hours (IQR: 12.2 to 29.7). Median seizure period was 16.5h (IQR: 7.0 to 49.7), median number of seizures per hour was 1.9 (IQR: 1.0 to 3.3). The seizure burden was 4.0 min/h (IQR: 2.0 to 7.0). There was no consistent pattern in the temporal evolution of seizures in neonates treated with TH. The skewness was neither positive nor negative (p-value=0.15), there was no difference between the duration of T1 and T2 (p-value=0.09) and no difference in the seizure burden between T1 and T2 (p=0.09). There was an association between Tmsb and Phenobarbital (PB) administration (r=0.76, p-value<0.001).

CONCLUSION

There is no consistent temporal evolution of seizure burden in neonates treated with TH. Seizures are diffuse, and their characteristics are variable.

Deep hypothermia for the treatment of refractory status epilepticus

In a rat model of status epilepticus (SE) induced by lithium and pilocarpine and refractory to midazolam, deep hypothermia (20 °C for 30 min) reduced EEG power over 50-fold, stopped SE within 12 min, and reduced EEG spikes by 87%. Hypothermia deserves further investigation as a treatment of last resort for refractory SE. This article is part of a Special Issue entitled "Status Epilepticus".

Seizures and hypothermia: importance of electroencephalographic monitoring and considerations for treatment

Hypoxic-ischemic encephalopathy is a common cause of seizures in neonates. Despite the introduction of therapeutic hypothermia, seizure rates are similar to those reported in the pre-therapeutic hypothermia era. However, the seizure profile has been altered resulting in a lower overall seizure burden, shorter individual seizure durations, and seizures that are harder to detect. Electroencephalographic (EEG) monitoring is the gold standard for detecting all seizures in neonates and this is even more critical in neonates who are cooled, as they are often sedated, making seizures more difficult to detect. Several studies have shown that the majority of seizures in neonates undergoing therapeutic hypothermia remain subclinical, thus requiring EEG monitoring for diagnosis. Amplitude-integrated EEG monitoring is useful but shorter duration seizures are more likely to be missed. Evidence is emerging about the pharmacokinetic profile of routinely used antiepileptic drugs during therapeutic hypothermia and some modifications have been suggested, particularly for lidocaine use.

Effect of depth and duration of cooling on deaths in the NICU among neonates with hypoxic ischemic encephalopathy: a randomized clinical trial

IMPORTANCE

Hypothermia at 33.5°C for 72 hours for neonatal hypoxic ischemic encephalopathy reduces death or disability to 44% to 55%; longer cooling and deeper cooling are neuroprotective in animal models.

OBJECTIVE

To determine if longer duration cooling (120 hours), deeper cooling (32.0°C), or both are superior to cooling at 33.5°C for 72 hours in neonates who are full-term with moderate or severe hypoxic ischemic encephalopathy.

DESIGN, SETTING, AND PARTICIPANTS

A randomized, 2 × 2 factorial design clinical trial performed in 18 US centers in the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) Neonatal Research Network between October 2010 and November 2013.

INTERVENTIONS

Neonates were assigned to 4 hypothermia groups; 33.5°C for 72 hours, 32.0°C for 72 hours, 33.5°C for 120 hours, and 32.0°C for 120 hours.

MAIN OUTCOMES AND MEASURES

The primary outcome of death or disability at 18 to 22 months is ongoing. The independent data and safety monitoring committee paused the trial to evaluate safety (cardiac arrhythmia, persistent acidosis, major vessel thrombosis and bleeding, and death in the neonatal intensive care unit [NICU]) after the first 50 neonates were enrolled, then after every subsequent 25 neonates. The trial was closed for emerging safety profile and futility analysis after the eighth review with 364 neonates enrolled (of 726 planned). This report focuses on safety and NICU deaths by marginal comparisons of 72 hours' vs 120 hours' duration and 33.5°C depth vs 32.0°C depth (predefined secondary outcomes).

RESULTS

The NICU death rates were 7 of 95 neonates (7%) for the 33.5°C for 72 hours group, 13 of 90 neonates (14%) for the 32.0°C for 72 hours group, 15 of 96 neonates (16%) for the 33.5°C for 120 hours group, and 14 of 83 neonates (17%) for the 32.0°C for 120 hours group. The adjusted risk ratio (RR) for NICU deaths for the 120 hours group vs 72 hours group was 1.37 (95% CI, 0.92-2.04) and for the 32.0°C group vs 33.5°C group was 1.24 (95% CI, 0.69-2.25). Safety outcomes were similar between the 120 hours group vs 72 hours group and the 32.0°C group vs 33.5°C group, except major bleeding occurred among 1% in the 120 hours group vs 3% in the 72 hours group (RR, 0.25 [95% CI, 0.07-0.91]). Futility analysis determined that the probability of detecting a statistically significant benefit for longer cooling, deeper cooling, or both for NICU death was less than 2%.

CONCLUSIONS AND RELEVANCE

Among neonates who were full-term with moderate or severe hypoxic ischemic encephalopathy, longer cooling, deeper cooling, or both compared with hypothermia at 33.5°C for 72 hours did not reduce NICU death. These results have implications for patient care and design of future trials.

TRIAL REGISTRATION

clinicaltrials.gov Identifier: NCT01192776.

Electrographic seizures are associated with brain injury in newborns undergoing therapeutic hypothermia

OBJECTIVE

Seizures are common among newborns with hypoxic-ischaemic encephalopathy (HIE) but the relationship between seizure burden and severity of brain injury among neonates receiving therapeutic hypothermia (TH) for HIE is unclear. We tested the hypothesis that seizure burden is associated with cerebral tissue injury independent of amplitude-integrated EEG (aEEG) background activity.

STUDY DESIGN

Term neonates undergoing 72 h of TH at four centres were selected for study if they had continuous aEEG and MRI. The aEEG with corresponding 2-channel raw EEG (aEEG/EEG), was classified by severity of background and seizure burden; MR images were classified by the severity of tissue injury.

RESULTS

Of 85 neonates, 52% had seizures on aEEG/EEG. Overall, 35% had high seizure burden, 49% had abnormal aEEG background in the first 24 h and 36% had severe injury on MRI. Seizures were most common on the first day, with significant recurrence during and after rewarming. Factors associated with severe injury on MRI were high seizure burden, poor aEEG background, 10 min Apgar and the need for more than one anticonvulsant. In multivariate logistic regression, high seizure burden was independently associated with greater injury on MRI (OR 5.00, 95% CI 1.47 to 17.05 p=0.01). Neither aEEG background, nor 10 min Apgar score were significant.

CONCLUSIONS

Electrographic seizure burden is associated with severity of brain injury on MRI in newborns with HIE undergoing TH, independent of degree of abnormality on aEEG background. Seizures are common during cooling, particularly on day 1, with a significant rebound on day 4.