Cerebral glucose metabolism and early EEG/aEEG in term newborn infants with hypoxic-ischemic encephalopathy

Brain perfusion imaging in neonates

•

MRI is the modality of choice to image and quantify cerebral perfusion.

•

Imaging of neonatal brain perfusion is possible using MRI and ultrasound.

•

Novel ultrafast ultrasound imaging allows for excellent spatiotemporal resolution.

•

Understanding cerebral hemodynamic changes of neonatal adaptation is key.

Abnormal variations of the neonatal brain perfusion can result in long-term neurodevelopmental consequences and cerebral perfusion imaging can play an important role in diagnostic and therapeutic decision-making. To identify at-risk situations, perfusion imaging of the neonatal brain must accurately evaluate both regional and global perfusion. To date, neonatal cerebral perfusion assessment remains challenging. The available modalities such as magnetic resonance imaging (MRI), ultrasound imaging, computed tomography (CT), near-infrared spectroscopy or nuclear imaging have multiple compromises and limitations. Several promising methods are being developed to achieve better diagnostic accuracy and higher robustness, in particular using advanced MRI and ultrasound techniques.

The objective of this state-of-the-art review is to analyze the methodology and challenges of neonatal brain perfusion imaging, to describe the currently available modalities, and to outline future perspectives.

Imaging Brain Metabolism in the Newborn

In this review, we discuss molecular brain imaging studies using positron emission tomography (PET) with 2-deoxy-2(¹⁸F)fluoro-d-glucose (FDG) in human newborns and infants, and illustrate how this technology can be applied to probe the neuropathophysiology of neonatal neurologic disorders. PET studies have been difficult to perform in sick babies because of patient transportation issues and suboptimal spatial resolution. With approval from the FDA and the institutional review board, we modified and installed the Focus 220 animal microPET scanner (Concorde Microsystems, Knoxville, TN) directly in our neonatal intensive care unit in Children's Hospital of Michigan and verified the high spatial resolution (<2 mm full-width-at-half-maximum) of this microPET. The neonatal pattern of glucose metabolism is very consistent, with the highest degree of activity in primary sensory and motor cortex, medial temporal region, thalamus, brain stem, and cerebellar vermis. Prior studies have shown that increases of glucose utilization are seen by 2 to 3 months in the parietal, temporal, cingulate, and primary visual cortex; basal ganglia; and cerebellar hemispheres. Between 6 and 8 months, lateral and inferior frontal cortex becomes more functionally active and, eventually, between 8 and 12 months, the dorsal and medial frontal regions also show a maturational increase. These findings are consistent with the physical, behavioral, and cognitive maturation of the infant. At birth, metabolic rates of glucose utilization in cortex are about 30% lower than in adults but rapidly rise such that, by 3 years, the cerebral cortical rates exceed adult rates by more than 2-fold. At around puberty, the rates for cerebral cortex begin to decline and gradually reach adult values by 16-18 years. These nonlinear changes of glucose utilization indirectly reflect programed periods of synaptic proliferation and pruning in the brain. Positron emission tomographic (PET) imaging of GABA_A receptors (using ¹¹C-flumazenil) in newborns also show a pattern very different from adults, with high binding in amygdala-hippocampus, sensory-motor cortex, thalamus, brain stem, and basal ganglia, in that order. We speculate that the early development of amygdala/hippocampus prepares the baby for bonding, attachment, and memory, and the deprivation of such experiences during a sensitive period results in malfunction of these networks and psychopathology, as has been shown in studies on severely socioemotionally deprived children. Recently developed hybrid PET/magnetic resonance (MR) scanners allow the simultaneous acquisition of PET and MR data sets with advanced applications. These devices are particularly advantageous for scanning babies and infants because of the high spatial resolution, automated coregistration of anatomical and functional images and, in the case of need for sedation, maximal data acquired in 1 session.

Dynamic FDG PET for assessing early effects of cerebral hypoxia and resuscitation in new-born pigs

PURPOSE

Changes in cerebral glucose metabolism may be an early prognostic indicator of perinatal hypoxic-ischaemic injury. In this study dynamic ¹⁸F-FDG PET was used to evaluate cerebral glucose metabolism in piglets after global perinatal hypoxia and the impact of the resuscitation strategy using room air or hyperoxia.

METHODS

New-born piglets (n = 16) underwent 60 min of global hypoxia followed by 30 min of resuscitation with a fraction of inspired oxygen (FiO₂) of 0.21 or 1.0. Dynamic FDG PET, using a microPET system, was performed at baseline and repeated at the end of resuscitation under stabilized haemodynamic conditions. MRI at 3 T was performed for anatomic correlation. Global and regional cerebral metabolic rates of glucose (CMRgl) were assessed by Patlak analysis for the two time-points and resuscitation groups.

RESULTS

Global hypoxia was found to cause an immediate decrease in cerebral glucose metabolism from a baseline level (mean ± SD) of 21.2 ± 7.9 to 12.6 ± 4.7 μmol/min/ 100 g (p <0.01). The basal ganglia, cerebellum and cortex showed the greatest decrease in CMRgl but no significant differences in global or regional CMRgl between the resuscitation groups were found.

CONCLUSION

Dynamic FDG PET detected decreased cerebral glucose metabolism early after perinatal hypoxia in piglets. The decrease in CMRgl may indicate early changes of mild cerebral hypoxia-ischaemia. No significant effect of hyperoxic resuscitation on the degree of hypometabolism was found in this early phase after hypoxia. Cerebral FDG PET can provide new insights into mechanisms of perinatal hypoxic- ischaemic injury where early detection plays an important role in instituting therapy.

Tc-99m-HL91 imaging in the early detection of neuronal injury in a neonatal rat model of hypoxic ischemia

OBJECTIVE

Hypoxic-ischemic insult in newborns results in progressive neuronal loss. For neuroprotective therapy to be effective, it is important to identify high-risk neonates soon after birth. 99mTc-labeled imaging agent, Tc-99m-HL91, developed as a putative hypoxic reagent, has been reported to demonstrate increased uptake in ischemic myocardium. We hypothesized that Tc-99m-HL91 is sensitive for the early identification of hypoxic-ischemic injury in neonatal rat brains.

DESIGN

Laboratory investigation.

SETTING

University research laboratory.

SUBJECTS

Sprague-Dawley rat pups.

INTERVENTIONS

Postnatal day-7 pups were divided into four groups: hypoxic-ischemia, hypoxia-only, ischemia-only, and controls. In the early (2 hrs), intermediate (20 hrs), and late (44 hrs) reoxygenation phases, Tc-99m-HL91 in vivo and ex vivo imaging and quantitative autoradiography were performed. Regions of interest were drawn to calculate the contrast ratio of Tc-99m-HL91 uptake between the ipsilateral and contralateral hemispheres. Pathology, cerebral blood flow, and blood-brain barrier damage were determined.

MEASUREMENTS AND MAIN RESULTS

After hypoxic-ischemia, there were very few pyknotic neurons in the early phase, many pyknotic neurons in the intermediate phase, and extensive neuronal loss in the late phase postreoxygenation. Blood-brain barrier damage occurred in the early phase, progressed in the intermediate phase, and became extensive in the late phase. The hypoxia-only and ischemia-only pups showed no neuronal or blood-brain barrier damage and had higher cerebral blood flow postreoxygenation compared with the hypoxia-ischemia pups. Regions of interest analysis of in vivo and ex vivo images and autoradiography revealed significantly higher Tc-99m-HL91 contrast ratio at early and intermediate phases, not late phase of hypoxic-ischemic group. Hypoxic-ischemia group had significantly higher contrast ratio values in the early and intermediate phases than the hypoxia-only and ischemia-only groups. A contrast ratio value of 0.15 in the early phase on postnatal day 7 had a sensitivity of 0.95 and specificity of 0.89 in detecting significant hypoxic-ischemic lesions on postnatal day 21.

CONCLUSION

Tc-99m-HL91 uptake is sensitive for the early detection of hypoxic-ischemic injury in neonatal brains.

Effects of morphine and midazolam on sleep-wake cycling in amplitude-integrated electroencephalography in post-surgical neonates ≥ 32 weeks of gestational age

BACKGROUND

Studies of children who undergo major non-cardiac surgery in the neonatal period are needed so that subsequent abnormal neurodevelopment can be better understood.

OBJECTIVE

It was the aim of our study to describe the influence of analgesic and sedative medication on the predominant background pattern and the development of sleep-wake cycling (SWC), as measured on amplitude-integrated electroencephalography (aEEG), in newborn infants born ≥ 32 weeks' gestation after major non-cardiac surgery.

METHODS

This prospective study included infants ≥ 32(+0) weeks' gestation admitted to the Neonatal Intensive Care Unit at The Royal Children's Hospital in Melbourne who were undergoing major non-cardiac surgery. Data on morphine and midazolam given after surgery were recorded and the BrainZ Monitor was applied post-operatively. The maximum levels of morphine and midazolam were assessed as predictors of time to aEEG outcomes using linear regression.

RESULTS

Forty-seven eligible infants were included. Emergence of SWC was observed at a mean of 13 h after surgery. The maximum dose of morphine or midazolam was not predictive of time to either any or developed SWC.

CONCLUSIONS

Despite high doses of morphine and midazolam, SWC was observed on aEEG in neonates ≥ 32 weeks' gestational age soon after major non-cardiac surgery. The aEEG background pattern was not affected by the maximum dose of either morphine or midazolam.

Children treated for epileptic encephalopathies show improved glucose metabolism

Epileptic neurological disorders in infants are often difficult to distinguish, and call for disparate treatments. Positron emission tomography (PET) using an [18F] fluoro-2-deoxyglucose (18FDG) tracer, is a powerful non-invasive technique successful in improving the diagnosis of a number of conditions. Interestingly, this technique has shown that cerebral glucose hypometabolism is present in children with epileptic encephalopathies (EE). Ten children with age-dependent EE were recruited and routine 18FDG PET images were evaluated for their ability to indicate cerebral glucose metabolism both before and after anti-epileptic treatment. We found that there is diffuse glucose hypometabolism in both hemispheres before treatment, indicating EE. Following treatment, the number of epileptic episodes significantly decreased (P < 0.05), while cerebral glucose metabolism improved. Our findings suggest that 18FDG PET can be utilized to monitor cerebral glucose metabolism as a measure of treatment progress in EE.

A combined a-EEG and MR spectroscopy study in term newborns with hypoxic-ischemic encephalopathy

OBJECTIVES

Brain damage following a perinatal hypoxic-ischemic (HI) insult has been documented by different diagnostic techniques. The aim of the present study was to relate a-EEG time course during the first 24h of life to brain metabolic changes detected by proton MR spectroscopy ((1)H-MRS) at 7-10days of life and to evaluate their correlation with outcome.

METHODS

Thirty-two patients with any grade HI encephalopathy were studied. Thirty-one out of 32 patients survived and underwent (1)H-MRS examination at 7-10days of life; a-EEG was recorded during the first 24h of life in 27/32 newborns; 26 patients underwent both examinations. Griffiths test, evaluation of motor skills, visual and hearing function were performed at regular intervals until the age of 2years.

RESULTS

a-EEG at 6, 12 and 24h of life showed a significant correlation with outcome. N-acetyl-aspartate/creatine (Cr), Lactate/Cr and myo-inositol differed significantly between patients with normal or poor outcome. a-EEG time course during the first 24h of life showed improvement in newborns with normal (1)H-MRS and good outcome and a deterioration in those with abnormal (1)H-MRS and poor outcome.

CONCLUSIONS

a-EEG time course may be able to document the severity and the evolution of the cerebral damage following an HI event. a-EEG is related to the severity of cerebral injury as defined by (1)H-MRS and both examinations showed a good correlation with outcome. These data, obtained in non-cooled infants, may represent reference data for future investigations in cooled infants.

Amplitude-integrated electroencephalography in neonates

Conventional electroencephalography (EEG) has been used for decades in the neonatal intensive care unit for formulating neurologic prognoses, demonstrating brain functional state and degree of maturation, revealing cerebral lesions, and identifying the presence and number of electrographic seizures. However, both the immediate availability of conventional EEG and the expertise with which it is interpreted are variable. Amplitude-integrated EEG provides simplified monitoring of cerebral function, and is rapidly gaining popularity among neonatologists, with growing use in bedside decision making and inclusion criteria for randomized clinical studies. Nonetheless, child neurologists and neurophysiologists remain cautious about relying solely on this tool and prefer interpreting conventional EEG. The present review examines the technical aspects of generating, recording, and interpreting amplitude-integrated EEG and contrasts this approach with conventional EEG. Finally, several proposed amplitude-integrated EEG classification schemes are reviewed. A clear understanding of this emerging technology of measuring brain health in the premature or sick neonate is critical in modern care of the newborn infant.

Effect of prenatal manganese intoxication on [(3)H]glucose uptake in the brain of rats lesioned as neonates with 6-hydroxydopamine

In the present study we examined the effects of prenatal manganese (Mn) intoxication on [(3)H]glucose uptake in the brain of rats lesioned as neonates with 6-hydroxydopamine (6-OHDA). MnCl(2) . 4H(2)O (10,000 ppm) was added to the drinking water of pregnant Wistar rats for the duration of pregnancy. On the day of parturition, Mn was discontinued as an additive to the drinking water. The control group consisted of rats that consumed water without Mn. Three days after birth, rats in both groups (control and Mn) were pretreated with desipramine hydrochloride (20 mg/kg) and pargyline hydrochloride (50 mg/kg) and injected bilaterally icv with one of three doses of 6-OHDA hydrobromide (15 mug, 30 mug or 67 mug base form in saline on each side) or with saline (control). 6-[(3)H]-D-glucose (500 muCi/kg, ip) was administered to male offspring in adulthood; after 15 min, brain specimens were taken (frontal cortex, hippocampus, striatum, thalamus with hypothalamus, pons and cerebellum) for determination of radioactivity in a liquid scintillation counter. Low dose 6-OHDA (15 mug icv) increased [(3)H]glucose uptake in all brain regions (p < 0.05) in both control and Mn-intoxicated animals. In rats lesioned with a moderate dose of 6-OHDA (30 mug icv), [(3)H]glucose uptake was unaltered in both control and Mn-exposed rats. High dose 6-OHDA (67 mug icv) reduced [(3)H]glucose uptake in all brain regions of Mn-exposed rats (except for cerebellum) compared with the saline group (all, p < 0.05). There was no change in regional brain uptake of [(3)H]glucose in control rats. In conclusion, this study shows that mild neuronal insult (15 mug icv 6-OHDA) increased glucose uptake in the brain while severe damage (concomitant 60 mug icv 6-OHDA and Mn treatment) significantly diminished this process.

The use of amplitude integrated electroencephalography for assessing neonatal neurologic injury

Amplitude-integrated electroencephalography (aEEG) plays an important role in integrated care of the full-term infant with neonatal encephalopathy. The three main features that are provided with aEEG are the background pattern on admission and the rate of recovery seen during the first 24 to 48 hours after birth, the presence of most electrographic discharges, and the effect of antiepileptic drugs.

Amplitude integrated electroencephalography in the full-term newborn

Amplitude-integrated electroencephalography (aEEG) is beginning to play an important role in the care of full-term infants who have neonatal encephalopathy. The three main features an aEEG provides include (1) the background pattern, showing the activity at admission to the neonatal intensive care unit and the rate of recovery during the first 24 to 48 hours after birth; (2) the presence or absence of sleep-wake cycling; and (3) the presence of most electrographic discharges.

The physiological basis for continuous electroencephalogram monitoring in the neonate

Continuous monitoring of the electrocortical activity as compared with intermittent recording sessions offers a possibility of revealing changes of the condition of the brain, relevant for clinical decisions. Furthermore, trend monitoring, such as amplitude integrated electroencephalogram (aEEG), helps the clinician in extracting features such as background activity, sleep-waking cycling, and seizure patterns, which have been proven relevant for prognosis and treatment of the preterm and sick term infant. A coherent model for classification and description of neonatal aEEG patterns is presented.

Amplitude-integrated EEG (aEEG) predicts outcome after cardiac arrest and induced hypothermia

OBJECTIVE

To evaluate the use of continuous amplitude-integrated EEG (aEEG) as a prognostic tool for survival and neurological outcome in cardiac arrest patients treated with hypothermia.

DESIGN

Prospective, observational study.

SETTING

Multidisciplinary intensive care unit in a university hospital.

INTERVENTION

Comatose survivors of cardiac arrest were treated with induced hypothermia for 24 h. An aEEG recording was initiated upon arrival at the ICU and continued until the patient regained consciousness or, if the patient remained in coma, no longer than 120 h. The aEEG recording was not available to the ICU physician, and the aEEG tracings were interpreted by a neurophysiologist with no knowledge of the patient's clinical status. Only clinically visible seizures were treated.

MEASUREMENTS AND RESULTS

Thirty-four consecutive hypothermia-treated cardiac arrest survivors were included. At normothermia (mean 37 h after cardiac arrest), the aEEG pattern was discriminative for outcome. All 20 patients with a continuous aEEG at this time regained consciousness, whereas 14 patients with pathological aEEG patterns (flat, suppression-burst or status epilepticus) did not regain consciousness and died in hospital. Patients were evaluated neurologically upon discharge from the ICU and after 6 months, using the Cerebral Performance Category (CPC) scale. Eighteen patients were alive with a good cerebral outcome (CPC 1--2) at 6-month follow-up.

CONCLUSION

A continuous aEEG pattern at the time of normothermia was discriminative for regaining consciousness. aEEG is an easily applied method in the ICU setting.

Role of cerebral function monitoring in the newborn

For many years, newborn infants admitted to neonatal intensive care units have had routine electrocardiography and been monitored for respiratory rate, heart rate, oxygen saturation, and blood pressure. Only recently has it also been considered important to monitor brain function using continuous electroencephalography. The role of cerebral function monitoring in sick full term and preterm infants is reviewed.

Sleep-wake cycling on amplitude-integrated electroencephalography in term newborns with hypoxic-ischemic encephalopathy

OBJECTIVE

The objective of this amplitude-integrated electroencephalography (aEEG) study was to evaluate the influence of perinatal hypoxia-ischemia on sleep-wake cycling (SWC) in term newborns and assess whether characteristics of SWC are of predictive value for neurodevelopmental outcome.

METHODS

From a consecutive series of newborns born during a 10-year period, the aEEG tracings of 171 term newborns with hypoxic-ischemic encephalopathy were assessed for the presence, time of onset, and quality of SWC. SWC patterns were categorized with regard to the background pattern on which they presented, as normal or abnormal SWC.

RESULTS

SWC was seen in 95.4% of the surviving newborns and in 8.1% of those who died. The median time intervals from birth to onset of SWC were significantly different in newborns with hypoxic-ischemic encephalopathy grades I, II, and III (7, 33, and 62 hours, respectively). Newborns with seizure discharges developed SWC with a delay of 30.5 hours. Good outcome was associated with earlier onset of SWC and normal SWC pattern. The difference in the median Griffiths' developmental quotients in newborns who started SWC before/after 36 hours was 8.5 points. The good/poor neurodevelopmental outcome was predicted correctly by the onset of SWC before/after 36 hours in 82% of newborns.

CONCLUSIONS

The presence, time of onset, and quality of SWC reflected the severity of the hypoxic-ischemic insult to which newborns were exposed. The time of onset of SWC has a predictive value for neurodevelopmental outcome.

Spectral analysis of burst periods in EEG from healthy and post-asphyctic full-term neonates

OBJECTIVE

To investigate whether the periodic EEG patterns seen in healthy and sick full term neonates (trace alternant and burst suppression, respectively) have different frequency characteristics.

METHODS

Burst episodes were selected from the EEGs of 9 healthy and 9 post-asphyctic full-term neonates and subjected to power spectrum analysis. Powers in two bands were estimated; 0-4 and 4-30 Hz, designated low- and high-frequency activity, respectively (LFA, HFA). The spectral edge frequency (SEF) was also assessed.

RESULTS

In bursts, the LFA power was lower in periods of burst suppression as compared to those of trace alternant. The parameter that best discriminated between the groups was the relative amount of low- and high-frequency activity. The SEF parameter had a low sensitivity to the group differences. In healthy neonates, the LFA power was higher over the posterior right as compared to the posterior left region.

CONCLUSIONS

Spectral power of low frequencies differs significantly between the burst episodes of healthy and sick neonates.

SIGNIFICANCE

These results can be used when monitoring cerebral function in neonates.