Use of therapeutic hypothermia for term infants with hypoxic-ischemic encephalopathy

Hypoxic-Ischemic Encephalopathy: Changing Outcomes Across the Spectrum

Neonatal hypoxic-ischemic encephalopathy (HIE) is a leading cause of death and neurodevelopmental impairment in neonates. Therapeutic hypothermia (TH) is the only established effective therapy and randomized trials affirm that TH reduces death and disability in moderate-to-severe HIE. Traditionally, infants with mild HIE were excluded from these trials due to the perceived low risk for impairment. Recently, multiple studies suggest that infants with untreated mild HIE may be at significant risk of abnormal neurodevelopmental outcomes. This review will focus on the changing landscape of TH, the spectrum of HIE presentations and their neurodevelopmental outcomes.

Short-term outcome of perinatal hypoxic-ischaemic encephalopathy at Chiang Mai University Hospital, Thailand: a 15-year retrospective study

BACKGROUND

The outcome of perinatal hypoxic-ischaemic encephalopathy (HIE) in middle-to-low-income countries varies between regions.

OBJECTIVES

To determine the mortality and morbidity, and factors influencing the deaths of infants with perinatal HIE.

METHODS

A retrospective study was conducted at Chiang Mai University Hospital, Thailand. Perinatal HIE infants of >35 weeks gestation, birthweight ≥2000 g and admitted during 2005-2019 were reviewed. Baseline Characteristics, clinical course and outcome at discharge were compared between the period before and after initiation of therapeutic hypothermia (TH). Risk of death in HIE infants who underwent TH was identified.

RESULTS

A total of 162 HIE infants were included. Compared to the period before TH initiation, the mortality rate was significantly decreased in the TH period. (27% vs. 12.8%, p=0.04) Among 100 HIE infants who underwent TH, the mortality rates was 14%(14/100), of whom 2.5% (2/76) and 50% (12/24) were in the moderate and severe HIE groups. Apgar score at 5 mins ≤1, severe HIE, seizures, hypoglycaemia, organ involvement ≥ five sites, ammonia ≥100 umol/L, lactate ≥14 mmol/L, and requirement for two or more inotropic drugs were risks of death. Multivariate analysis demonstrated that severe HIE (aOR 732.8, 95% CI 4.7-114643, p=0.01) and a need for two or more inotropic drugs (aOR 45.7, 95% CI 1.5-1040, p=0.029) were significant factors for mortality.

CONCLUSION

In the period of TH, perinatal HIE infants had decreased mortality. Severe HIE and a need for two or more inotropic drugs were associated with death in the infant with HIE who underwent TH.Abbreviations: AED: anti-epileptic drug; BW, birthweight; CI: confidence interval; CMU: Chiang Mai University; EEG: electro-encephalogram; GA: gestational age; HIE: hypoxic-ischaemic encephalopathy; IQR: interquartile range; NICU: neonatal intensive care unit; SD: standard deviation; TH: therapeutic hypothermia.

Early detection of neonatal hypoxic-ischemic white matter injury: an MR diffusion tensor imaging study

The purpose of this study was to compare diffusion tensor metrics in normal age-matched neonates with survivors of hypoxic–ischemic encephalopathy (HIE) and extracorporeal membrane oxygenation (ECMO). Thirty-five normal, 27 HIE, and 13 ECMO infants underwent MRI at 3 T. Neurodevelopmental assessments were performed. Fractional anisotropy (FA), axial diffusivity (AD), and radial diffusivity (RD) of the inferior fronto-occipital fasciculus, inferior longitudinal fasciculus, anterior commissure, genu corpus callosum and splenium of the corpus callosum, anterior and posterior limb of the internal capsule, superior longitudinal fasciculus, and the centrum semiovale were analyzed with tract-based spatial statistics modified for use in neonates. Linear regression analysis was performed, and 95% confidence intervals were created for age effects on the tensor metrics with the control patients. Two-sample t-test was done to determine whether there was a difference in the tensor metrics between the normal and patient cohort. There was a statistically significant age effect on the FA and RD in the selected regions of the brain (F<0.05) and a group difference in the FA and RD between the normal and the HIE group (P<0.05). The group difference in the FA and RD between the normal and ECMO groups was seen in the anterior commissure, genu corpus callosum, right inferior longitudinal fasciculus, fronto-occipital fasciculus, centrum semiovale, and superior longitudinal fasciculus (P<0.05). Patients who were outside the 95% confidence intervals of the FA, AD, and RD overlapped with those with abnormalities clinically and on the conventional MRI. In conclusion, diffusion tensor imaging can play a significant role in detecting infants with early indications of hypoxic–ischemic brain injury.

Cerebral Hemodynamics in Asphyxiated Newborns Undergoing Hypothermia Therapy: Pilot Findings Using a Multiple-Time-Scale Analysis

BACKGROUND

Improved quantitative assessment of cerebral hemodynamics in newborns might enable us to optimize cerebral perfusion. Our objective was to develop an approach to assess cerebral hemodynamics across multiple time scales during the first 72 hours of life in newborns during hypothermia therapy.

METHODS

Spontaneous oscillations in mean arterial pressure and regional cerebral tissue oxygen saturation were analyzed using a moving window correlation method with time scales ranging from 0.15 to 8 hours in this pilot methodology study. Abnormal neurodevelopmental outcome was defined by Bayley III scores and/or cerebral palsy by age 24 months using receiver operating curve.

RESULTS

Multiple-time-scale correlations between the mean arterial pressure and regional cerebral tissue oxygen saturation oscillations were tested in 10 asphyxiated newborns undergoing hypothermia therapy. Large noninduced fluctuations in the blood pressure were observed during cooling in all five infants with abnormal outcomes. Notably, these infants had two distinct patterns of correlation: a positive in-phase correlation at the short time scales (15 minutes) and/or a negative antiphase correlations observed at long time scales (4 hours.). Both the in-phase (area under the curve 0.6, [95% confidence interval 0.2-0.95]) and antiphase correlations (area under the curve 0.75, [95% confidence interval 0.4-0.95]) appeared to be related to an abnormal outcome.

CONCLUSIONS

Our observations suggest that the time scale is an important factor that needs to be standardized in the assessment of neonatal cerebral hemodynamics.

Wavelet coherence analysis of dynamic cerebral autoregulation in neonatal hypoxic-ischemic encephalopathy

Cerebral autoregulation represents the physiological mechanisms that keep brain perfusion relatively constant in the face of changes in blood pressure and thus plays an essential role in normal brain function. This study assessed cerebral autoregulation in nine newborns with moderate-to-severe hypoxic–ischemic encephalopathy (HIE). These neonates received hypothermic therapy during the first 72 h of life while mean arterial pressure (MAP) and cerebral tissue oxygenation saturation (S_ctO₂) were continuously recorded. Wavelet coherence analysis, which is a time-frequency domain approach, was used to characterize the dynamic relationship between spontaneous oscillations in MAP and S_ctO₂. Wavelet-based metrics of phase, coherence and gain were derived for quantitative evaluation of cerebral autoregulation. We found cerebral autoregulation in neonates with HIE was time-scale-dependent in nature. Specifically, the spontaneous changes in MAP and S_ctO₂ had in-phase coherence at time scales of less than 80 min (< 0.0002 Hz in frequency), whereas they showed anti-phase coherence at time scales of around 2.5 h (~ 0.0001 Hz in frequency). Both the in-phase and anti-phase coherence appeared to be related to worse clinical outcomes. These findings suggest the potential clinical use of wavelet coherence analysis to assess dynamic cerebral autoregulation in neonatal HIE during hypothermia.

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Cerebral hemodynamics in HIE neonates were continuously recorded in hypothermia.

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Wavelet coherence can be used to assess dynamic autoregulation in HIE neonates.

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Wavelet-derived metrics have about 88.9% accuracy in predicting clinical outcomes.

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Wavelet phase, coherence, and gain are validated against transfer function analysis.

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Cerebral autoregulation in HIE neonates is time-scale-dependent in a wide range.

The "neurovascular unit approach" to evaluate mechanisms of dysfunctional autoregulation in asphyxiated newborns in the era of hypothermia therapy

Despite improvements in obstetrical and neonatal care, and introduction of hypothermia as a neuroprotective therapy, perinatal brain injury remains a frequent cause of cerebral palsy, mental retardation and epilepsy. The recognition of dysfunction of cerebral autoregulation is essential for a real time measure of efficacy to identify those who are at highest risk for brain injury. This article will focus on the "neurovascular unit" approach to the care of asphyxiated neonates and will address 1) potential mechanisms of dysfunctional cerebral blood flow (CBF) regulation, 2) optimal monitoring methodology such as NIRS (near infrared spectroscopy), and TCD (transcutaneous Doppler), and 3) clinical implications of monitoring in the neonatal intensive care setting in asphyxiated newborns undergoing hypothermia and rewarming. Critical knowledge of the functional regulation of the neurovascular unit may lead to improved ability to predict outcomes in real time during hypothermia, as well as differentiate non-responders who might benefit from additional therapies.

Neuroprotective therapies after perinatal hypoxic-ischemic brain injury

Hypoxic-ischemic (HI) brain injury is one of the main causes of disabilities in term-born infants. It is the result of a deprivation of oxygen and glucose in the neural tissue. As one of the most important causes of brain damage in the newborn period, the neonatal HI event is a devastating condition that can lead to long-term neurological deficits or even death. The pattern of this injury occurs in two phases, the first one is a primary energy failure related to the HI event and the second phase is an energy failure that takes place some hours later. Injuries that occur in response to these events are often manifested as severe cognitive and motor disturbances over time. Due to difficulties regarding the early diagnosis and treatment of HI injury, there is an increasing need to find effective therapies as new opportunities for the reduction of brain damage and its long term effects. Some of these therapies are focused on prevention of the production of reactive oxygen species, anti-inflammatory effects, anti-apoptotic interventions and in a later stage, the stimulation of neurotrophic properties in the neonatal brain which could be targeted to promote neuronal and oligodendrocyte regeneration.

Therapeutic hypothermia: treatment for hypoxic-ischemic encephalopathy in the NICU

Baby M was born limp, blue, and without respiratory effort at 38 weeks gestation to a 38-year-old, gravida 5, para 1, woman. Delivery was vaginal after a rapid progression of labor leaving no opportunity for a cesarean section. No other complications were noted during labor but a large surge at delivery, later diagnosed as uterine rupture, initially raised concerns about placental abruption. Apgar scores were 1, 2, and 4 at one, five, and ten minutes, respectively. She was resuscitated in the delivery room, intubated, and transferred in critical condition to the neonatal intensive care unit (NICU) at the birth hospital. Her initial cord pH was 6.7 and was slightly improved at 7.17 on arterial blood gas after resuscitation. Our NICU team was consulted because of her severe neurologic depression. The birth hospital was within walking distance of our tertiary care center and our neurologists went to evaluate her for the hypothermia protocol. Her neurologic exam was notable for dilated and unresponsive pupils, no spontaneous movements, and diminished reflexes and tone, consistent with moderate-to-severe encephalopathy. Seizure activity began at one hour of age and consisted of lip smacking, which was later confirmed by electroencephalogram (EEG). Enrollment criteria were met based on respiratory depression at birth requiring intubation and continued need for ventilation, concern for placental abruption, cord pH less than 7, and encephalopathy on exam and EEG. After stabilizing her airway and achieving central access to treat acidosis and seizures, the team prepared her for transfer to our NICU. At this point, the primary concern became her neurologic status.

White-gray matter echogenicity ratio and resistive index: sonographic bedside markers of cerebral hypoxic-ischemic injury/edema?

OBJECTIVE

Head ultrasonography (HUS) is a reliable and easy to perform bedside imaging technique that can give valuable information about degree of brain injury/edema after perinatal asphyxia in term neonates. The goals of our study were to determine whether semiquantitative markers such as standardized white matter/gray matter (WM/GM) echogenicity ratio and resistive index (RI) value measured by HUS differs between asphyxiated term neonates and healthy controls.

STUDY DESIGN

Thirty-one carefully selected term neonates who suffered from perinatal hypoxic-ischemic encephalopathy (HIE) were included in the study. The ratio of the WM/GM echogenicity of the cingulate gyrus was calculated. In addition, the RI value was measured in the anterior cerebral artery. US scalars were compared with 11 healthy neonates.

RESULT

WM/GM ratio is significantly increased and RI value significantly decreased in asphyxiated term neonates compared with healthy subjects.

CONCLUSION

WM/GM ratio and RI value allows discriminating between asphyxiated neonates and healthy subjects. These US scalars may serve as valuable, easy to acquire semiquantitative bedside markers of brain HIE, when magnetic resonance imaging is unavailable or cannot be performed in the acute setting.

The S.T.A.B.L.E.® Program: the evidence behind the 2012 update

First released in 1996, the S.T.A.B.L.E.® Program has provided evidence-based education in the postresuscitation and pretransport stabilization care of sick newborns to more than a quarter million multidisciplinary perinatal healthcare team members from around the world. The program, aimed at preventing the leading causes of neonatal mortality, continues to be the subject of published peer-reviewed research and is periodically updated to ensure relevancy and inclusion of current best evidence. S.T.A.B.L.E. is a mnemonic for the 6 essential assessment parameters taught in the program: Sugar and Safe care, Temperature, Airway, Blood pressure, Lab work, and Emotional support. This mnemonic was specifically chosen to serve as a memory tool to remind staff of "what to do" during those infrequent but stressful times when they were expected to assess and stabilize sick newborns. Course completion of the S.T.A.B.L.E. Program is obtained as a result of didactic training and successful completion of content testing. The program's test questions are periodically evaluated and revised on the basis of psychometric analysis. The 6th edition of the S.T.A.B.L.E. Program learner/provider manual is scheduled for release in 2012 and will reflect the latest in stabilization guidelines throughout the program's 6 modules and supplemental content.

A quantitative analysis of optimal treatment capacity for perinatal asphyxia

OBJECTIVE

In centers electing to offer therapeutic hypothermia for treating hypoxic-ischemic encephalopathy (HIE), determining the optimal number of cooling devices is not straightforward. The authors used computer-based modeling to determine the level of service as a function of local HIE caseload and number of cooling devices available.

METHODS

The authors used discrete event simulation to create a model that varied the number of HIE cases and number of cooling devices available. Outcomes of interest were percentage of HIE-affected infants not cooled, number of infants not cooled, and percentage of time that all cooling devices were in use.

RESULTS

With 1 cooling device, even the smallest perinatal center did not achieve a cooling rate of 99% of eligible infants. In contrast, 2 devices ensured 99% service in centers treating as many as 20 infants annually. In centers averaging no more than 1 HIE infant monthly, the addition of a third cooling device did not result in a substantial reduction in the number of infants who would not be cooled.

CONCLUSION

Centers electing to offer therapeutic hypothermia with only a single cooling device are at significant risk of being unable to provide treatment to eligible infants, whereas 2 devices appear to suffice for most institutions treating as many as 20 annual HIE cases. Three devices would rarely be needed given current caseloads seen at individual institutions. The quantitative nature of this analysis allows decision makers to determine the number of devices necessary to ensure adequate availability of therapeutic hypothermia given the HIE caseload of a particular institution.

Hypoxic Ischemic Encephalopathy: Pathophysiology and Experimental Treatments

Hypoxic ischemic encephalopathy (HIE) is a serious birth complication affecting full term infants: 40-60% of affected infants die by 2 years of age or have severe disabilities. The majority of the underlying pathologic events of HIE are a result of impaired cerebral blood flow and oxygen delivery to the brain with resulting primary and secondary energy failure. In the past, treatment options were limited to supportive medical therapy. Currently, several experimental treatments are being explored in neonates and animal models to ameliorate the effects of secondary energy failure. This review discusses the underlying pathophysiologic effects of a hypoxic-ischemic event and experimental treatment modalities being explored to manage infants with HIE. Further research is needed to better understand if the long-term impact of the experimental treatments and whether the combinations of experimental treatments can improve outcomes in infants with HIE.

Neuroprotective approaches: before and after delivery

Infants born preterm are especially vulnerable to cerebral palsy, the risk of which is inversely proportional to gestational age at birth. The contribution of prematurity to the overall burden of cerebral palsy is substantial. This article reviews and discusses potential antenatal and postnatal neuroprotective approaches targeted at the numerous risk factors associated with cerebral palsy among preterm infants, including magnesium sulfate.

Hypothermia for the treatment of infants with hypoxic-ischemic encephalopathy

Neonatal encephalopathy affects 2 to 5 of every 1000 live births and represents a major cause of mortality and long-term morbidity in affected infants. Hypoxic ischemic encephalopathy (HIE) is the major cause of encephalopathy in the neonatal period. Until recently, management of a newborn with encephalopathy has consisted largely of supportive care to restore and maintain cerebral perfusion, provide adequate gas exchange and treat seizure activity. Recent randomized controlled trials have shown that mild therapeutic hypothermia (cooling) initiated within 6 h of birth reduces death and disability in these infants. Cooling can be accomplished through whole-body cooling or selective head cooling. Meta-analysis of these trials suggests that for every six or seven infants with moderate to severe HIE who are treated with mild hypothermia, there will be one fewer infant who dies or has significant neurodevelopmental disability. In response to this evidence, major policy makers and guideline developers have recommended that cooling therapy be offered to infants with moderate to severe HIE. The dissemination of this new therapy will require improved identification of infants with HIE and regional commitment to allow these infants to be cared for in a timely manner.

Noninvasive cerebral perfusion imaging in high-risk neonates

Advances in medical and surgical care of the high-risk neonate have led to increased survival. A significant number of these neonates suffer from neurodevelopmental delays and failure in school. The focus of clinical research has shifted to understanding events contributing to neurological morbidity in these patients. Assessing changes in cerebral oxygenation and regulation of cerebral blood flow (CBF) is important in evaluating the status of the central nervous system. Traditional CBF imaging methods fail for both ethical and logistical reasons. Optical near infrared spectroscopy (NIRS) is increasingly being used for bedside monitoring of cerebral oxygenation and blood volume in both very low birth weight infants and neonates with congenital heart disease. Although trends in CBF may be inferred from changes in cerebral oxygenation and/or blood volume, NIRS does not allow a direct measure of CBF in these populations. Two relatively new modalities, arterial spin-labeled perfusion magnetic resonance imaging and optical diffuse correlation spectroscopy, provide direct, noninvasive measures of cerebral perfusion suitable for the high-risk neonates. Herein we discuss the instrumentation, applications, and limitations of these noninvasive imaging techniques for measuring and/or monitoring CBF.