Cerebral function monitor studies in neonates

Neuromonitoring in neonatal intensive care units-an important need towards individualized neuroprotective care

Neuromonitoring has been widely accepted as an important part in neonatal care. Amplitude-integrated EEG (aEEG) and near-infrared spectroscopy (NIRS) are often mentioned in this context, though being only a part of the fully array of methods and examinations that could be considered neuromonitoring. Within the broad array of medical conditions that could be encountered in a neonatal patient, it is important to be aware of the indications for neuromonitoring and especially which neuromonitoring technique to use best for the individual condition. aEEG is now a widely accepted neuromonitor in neonatology with its value in hypoxic events and seizures only rarely questioned. Other methods like NIRS still have to prove themselves in the future. The SafeBoosC-III trial showed that it still remains difficult for some of these methods to prove their value for the improvement of outcome. Bute future developments such as multimodal neuromonitoring with data integration and artificial intelligence analysis could improve the value of these methods.

Amplitude Integrated Electroencephalography - Reference Values in Children aged 2 months to 16 years

AIM

Amplitude integrated electroencephalography (aEEG) is a bedside neuromonitoring tool, standard within neonatal critical care provision. Its application in children is increasing but normative data underpinning such use are lacking. We present a dataset of normative aEEG values for children aged 2 months to 16 years.

METHODS

This retrospective observational cohort study derives aEEG normative amplitude characteristics from electroencephalograms (EEGs) recorded in Children's Health Ireland at Crumlin. aEEG was derived from 350 normal EEGs, recorded in children aged 2 months to 16 years. Supplementary aEEGs were derived from children with abnormal EEG traces. Median upper and lower margin amplitudes, and bandwidth were calculated from 5-minute waking and sleeping EEG epochs.

RESULTS

aEEG amplitudes vary with age and state, increasing over the first two years of life before diminishing. Upper and lower margin amplitudes, and bandwidth are greater during sleep for children < 6 years. Reference ranges may be cohorted into 2 groups (upper and lower reference limits; < 6 years - 38μV/7μV awake, 54μV/10μV asleep; > 6 years - 33μV/5μV awake, 36μV/6μV asleep) CONCLUSION: aEEG traces evolve with age in childhood and differ from neonatal values. We provide a comprehensive set of aEEG normatives to facilitate clinical interpretation in older children.

Amplitude-Integrated EEG Monitoring in Pediatric Intensive Care: Prognostic Value in Meningitis before One Year of Age

Pediatric morbidity from meningitis remains considerable. Preventing complications is a major challenge to improve neurological outcome. Seizures may reveal the meningitis itself or some complications of this disease. Amplitude-integrated electroencephalography (aEEG) is gaining interest for the management of patients with acute neurological distress, beyond the neonatal age. This study aimed at evaluating the predictive value of aEEG monitoring during the acute phase in meningitis among a population of infants hospitalized in the pediatric intensive care unit (PICU), and at assessing the practicability of the technique. AEEG records of 25 infants younger than one year of age hospitalized for meningitis were retrospectively analyzed and correlated to clinical data and outcome. Recording was initiated, on average, within the first six hours for n = 18 (72%) patients, and overall quality was considered as good. Occurrence of seizure, of status epilepticus, and the background pattern were significantly associated with unfavorable neurological outcomes. AEEG may help in the management and prognostic assessment of pediatric meningitis. It is an easily achievable, reliable technique, and allows detection of subclinical seizures with minimal training. However, it is important to consider the limitations of aEEG, and combinate it with conventional EEG for the best accuracy.

Amplitude-Integrated Electroencephalography: A Primer for Neonatologists and Practitioners in the NICU

Amplitude-integrated electroencephalography (aEEG) is an essential tool used in the NICU to monitor infants with central nervous system pathology and encephalopathy. This review provides a summary of aEEG, including clinical indications, interpretation of different tracing patterns, and seizure identification, which are essential skills for teams caring for sick newborns. We also discuss the limitations of the clinical application of aEEG in this population.

Early aEEG can predict neurodevelopmental outcomes at 12 to 18 month of age in VLBWI with necrotizing enterocolitis: a cohort study

Background

Studies have shown that neurological damage is common in necrotizing enterocolitis (NEC) survivors. The purpose of the study was to investigate the predictive value of amplitude-integrated electroencephalogram (aEEG) for neurodevelopmental outcomes in preterm infants with NEC.

Methods

Infants with NEC were selected, and the control group was selected based on 1:1–2 pairing by gestational age. We performed single-channel (P3–P4) aEEG in the two groups. The Burdjalov scores were compared between the two groups. Cranial magnetic resonance imaging (MRI) was performed several months after birth. The neurological outcomes at 12 to 18 months of age were compared with the Gesell Developmental Schedules (GDS). The predictive value of aEEG scores for neurodevelopmental delay was calculated.

Results

There was good consistency between the two groups regarding general conditions. In the 1st aEEG examination, the patients in NEC group had lower Co (1.0 (0.0, 2.0) vs. 2.0 (2.0, 2.0), P = 0.001), Cy (1.0 (0.0, 2.0) vs. 3.0 (3.0, 4.0), P < 0.001), LB (1.0 (0.0, 2.0) vs. 2.0 (2.0, 2.0), P < 0.001), B (1.0 (1.0, 2.0) vs. 3.0 (3.0, 3.5), P < 0.001) and T (3.0 (2.0, 8.0) vs. 10.0 (10.0, 11.5), P < 0.001), than the control group. Cranial MRI in NEC group revealed a widened interparenchymal space with decreased myelination. The abnormality rate of cranial MRI in the NEC group was higher than that in the control group (P = 0.001). The GDS assessment indicated that NEC children had inferior performance and lower mean scores than the control group in the subdomains of gross motor (71 (SD = 6.41) vs. 92 (SD = 11.37), P < 0.001), fine motor (67 (SD = 9.34) vs. 96 (SD = 13.69), adaptive behavior (76 (SD = 9.85) vs. 95 (SD = 14.38), P = 0.001), language (68 (SD = 12.65) vs. 95 (SD = 11.41), P < 0.001), personal-social responses (80 (SD = 15.15) vs. 93(SD = 14.75), P = 0.037) and in overall DQ (72 (SD = 8.66) vs. 95 (SD = 11.07), P < 0.001). The logistic binary regression analysis revealed that the NEC patients had a significantly greater risk of neurodevelopmental delay than the control group (aOR = 27.00, 95% CI = 2.561–284.696, P = 0.006). Confirmed by Spearman’s rank correlation analysis, neurodevelopmental outcomes were significantly predicted by the 1st aEEG Burdjalov score (r = 0.603, P = 0.001). An abnormal 1st Burdjalov score has predictive value for neurodevelopmental delay with high specificity (84.62%) and positive predictive value (80.00%).

Conclusions

Children with NEC are more likely to develop neurodevelopmental delay. There is high specificity and PPV of early aEEG in predicting neurodevelopmental delay.

Newborn Sleep: Patterns, Interventions, and Outcomes

Sleep is a necessary function of life. Fetuses and neonates spend most of their day sleeping, making it paramount to place emphasis on adequate and optimal sleep. As the current body of literature continues to expand, we have increased our understanding of sleep and its role in development. Sleep disturbances, particularly early in life can affect all aspects of health such as neurological development, emotional well-being, and overall growth. This article aims to provide a primer on sleep development from fetal life into the neonatal period, discuss sleep in both the home and hospital settings, explore the tools used to measure sleep, and review common interventions applied to those infants experiencing poor sleep. Lastly, there is a mention of long-term outcomes and how early recognition and implementation of measures could help to improve overall growth and development throughout childhood. [Pediatr Ann. 2020;49(2):e82-e87.].

Amplitude-integrated electroencephalography for neonatal seizure detection. An electrophysiological point of view

Seizures in the newborn are associated with high morbidity and mortality, making their detection and treatment critical. Seizure activity in neonates is often clinically obscured, such that detection of seizures is particularly challenging. Amplitude-integrated EEG is a technique for simplified EEG monitoring that has found an increasing clinical application in neonatal intensive care. Its main value lies in the relative simplicity of interpretation, allowing nonspecialist members of the care team to engage in real-time detection of electrographic seizures. Nevertheless, to avoiding misdiagnosing rhythmic artifacts as seizures, it is necessary to recognize the electrophysiological ictal pattern in the conventional EEG trace available in current devices. The aim of this paper is to discuss the electrophysiological basis of the differentiation of epileptic seizures and extracranial artifacts to avoid misdiagnosis with amplitude-integrated EEG devices.

The development of neonatal neurointensive care

Brain injury remains one of the major unsolved problems in neonatal care, with survivors at high risk of lifelong neurodisability. It is unlikely that a single intervention can ameliorate neonatal brain injury, given the complex interaction between pathological processes, developmental trajectory, genetic susceptibility, and environmental influences. However, a coordinated, interdisciplinary approach to understand the root cause enables early detection, and diagnosis with enhanced clinical care offering the best chance of improving outcomes and facilitate new lines of neuroprotective treatments. Adult neurointensive care has existed as a speciality in its own right for over 20 years; however, it is only recently that large prospective studies have demonstrated the benefit of this model of care. The 'Neuro-intensive Care Nursery' model originated at the University of California San Francisco in 2008, and since then a growing number of units worldwide have adopted this approach. As well as providing consistent coordinated care for infants from a multidisciplinary team, it provides opportunities for specialist education and training in neonatal neurology, neuromonitoring, neuroimaging and nursing. This review outlines the origins of brain-oriented care of the neonate and the development of the Neuro-NICU (neonatal intensive care unit) and discusses some of the challenges and opportunities in expanding this model of care.

Swedish consensus reached on recording, interpretation and reporting of neonatal continuous simplified electroencephalography that is supported by amplitude-integrated trend analysis

Continuous monitoring of electroencephalography (EEG), with a focus on amplitude-integrated EEG (aEEG), has been used in neonatal intensive care for decades. A number of systems have been suggested for describing and quantifying aEEG patterns. Extensive full-montage EEG monitoring is used in specialised intensive care units. The American Clinical Neurophysiology Society published recommendations for defining and reporting EEG findings in critically ill adults and infants. Swedish neonatologists and clinical neurophysiologists collaborated to optimise simplified neonatal continuous aEEG and EEG recordings based on these American documents.

CONCLUSION

This paper describes the Swedish consensus document produced by those meetings.

Amplitude-integrated electroencephalography for seizure detection in newborn infants

The amplitude-integrated electroencephalogram (aEEG) is a filtered and compressed EEG trend that can be used for long-term monitoring of brain function in patients of all ages. aEEG is increasingly used in neonatal intensive care units since several studies have shown its utility in high-risk newborn infants. Main indications for aEEG monitoring include early evaluation of brain function after perinatal asphyxia and seizure detection. The aEEG is usually recorded from one or two channels derived from parietal, central, or frontal leads. Although the aEEG is very useful for identifying high-risk infants and infants with seizures, the compressed trend has limitations with regards to detection of individual seizures. However, modern monitors also display the corresponding EEG (aEEG/EEG), which increases the probability of detecting single brief seizures. For improved evaluation of electrocortical brain activity the aEEG/EEG should be assessed together with repeated conventional EEGs or multi-channel EEG monitoring in a multi-disciplinary team.

Sleep Disturbances in Newborns

The purpose of this review is to serve as an introduction to understanding sleep in the fetus, the preterm neonate and the term neonate. Sleep appears to have numerous important roles, particularly in the consolidation of new information. The sleep cycle changes over time, neonates spend the most time in active sleep and have a progressive shortening of active sleep and lengthening of quiet sleep. Additionally, the sleep cycle is disrupted by many things including disease state and environment, and the amplitude integrated EEG can be a useful tool in evaluating sleep, and sleep disturbances, in neonates. Finally, there are protective factors for infant sleep that are still being studied.

Application of an Amplitude-integrated EEG Monitor (Cerebral Function Monitor) to Neonates

Amplitude-integrated EEG (aEEG) is an easily accessible technique to monitor the electrocortical activity in preterm and term infants in neonatal intensive care units (NICUs). This method was first used to monitor newborns after asphyxia, providing information about future neurological outcomes. The aEEG is also helpful to select newborns who benefit from cooling. The aEEG monitoring of preterm infants is becoming more widespread, as various studies have shown that neurodevelopmental outcome is related to early aEEG tracings. Here, we demonstrate the application of the aEEG monitoring system and present typical patterns that depend upon gestational age and pathophysiological conditions. Furthermore, we mention pitfalls in the interpretation of the aEEG, as this method requires accurate fixation and localization of the electrodes. Additionally, the raw EEG can be used to detect neonatal seizures or to identify aEEG application problems. In conclusion, aEEG is a safe and generally well-tolerated method for the bedside monitoring of neonatal cerebral function; it can even provide information about long-term outcome.

Reference values for three channels of amplitude-integrated EEG using the Brainz BRM3 cerebral function monitor in normal term neonates: a pilot study

BACKGROUND

Amplitude-integrated electroencephalography (EEG) is a form of continuous EEG using a select number of electrodes (2-4), which can be used for bedside monitoring of brain functions in critically ill neonates. There is a paucity of normative amplitude-integrated EEG data for term healthy neonates especially for unilateral channels that are available for newer cerebral function monitors.

OBJECTIVE

To define absolute amplitudes for all three available channels and also to determine if route of delivery or presence of a caput succedaneum would affect amplitude-integrated EEG amplitude voltages.

METHODS

This is a prospective observational study of 80 healthy term neonates (gestational age ≥ 38 weeks) who had three-channel amplitude-integrated EEG recorded for 90 minutes within 12 hours of birth using the Brainz BRM3 cerebral function monitor.

RESULTS

Median maximum and median minimum voltages obtained were 16.96 μV and 8.13 μV for the cross-cerebral (CC), 14.42 μV and 7.13 μV for the right unilateral, and 13.16 μV and 6.51 μV for the left unilateral aEEG channels, respectively. There were no statistically significant difference amplitude voltages for any channel based on route of delivery. The presence of a caput succedaneum was associated with a decrease in the median and mean of the maximum and minimum amplitude voltages for CC channel. Median maximum and median minimum voltages for the CC channel among the caput and normal scalp examination groups were 14.62 μV vs 17.27 μV (P = 0.022) and 7.21 μV vs 8.24 μV (P = 0.004), respectively. Similarly, mean maximum and mean minimum voltages for the CC channel were 15.42 μV vs 17.59 μV (P = 0.038) and 7.27 μV vs 8.25 μV (P = 0.005) in the caput and normal scalp examination groups, respectively.

A random forest model based classification scheme for neonatal amplitude-integrated EEG

BACKGROUND

Modern medical advances have greatly increased the survival rate of infants, while they remain in the higher risk group for neurological problems later in life. For the infants with encephalopathy or seizures, identification of the extent of brain injury is clinically challenging. Continuous amplitude-integrated electroencephalography (aEEG) monitoring offers a possibility to directly monitor the brain functional state of the newborns over hours, and has seen an increasing application in neonatal intensive care units (NICUs).

METHODS

This paper presents a novel combined feature set of aEEG and applies random forest (RF) method to classify aEEG tracings. To that end, a series of experiments were conducted on 282 aEEG tracing cases (209 normal and 73 abnormal ones). Basic features, statistic features and segmentation features were extracted from both the tracing as a whole and the segmented recordings, and then form a combined feature set. All the features were sent to a classifier afterwards. The significance of feature, the data segmentation, the optimization of RF parameters, and the problem of imbalanced datasets were examined through experiments. Experiments were also done to evaluate the performance of RF on aEEG signal classifying, compared with several other widely used classifiers including SVM-Linear, SVM-RBF, ANN, Decision Tree (DT), Logistic Regression(LR), ML, and LDA.

RESULTS

The combined feature set can better characterize aEEG signals, compared with basic features, statistic features and segmentation features respectively. With the combined feature set, the proposed RF-based aEEG classification system achieved a correct rate of 92.52% and a high F1-score of 95.26%. Among all of the seven classifiers examined in our work, the RF method got the highest correct rate, sensitivity, specificity, and F1-score, which means that RF outperforms all of the other classifiers considered here. The results show that the proposed RF-based aEEG classification system with the combined feature set is efficient and helpful to better detect the brain disorders in newborns.

Multi-channel amplitude-integrated EEG characteristics in preterm infants with a normal neurodevelopment at two years of corrected age

AIM

To analyze quantitatively multi-channel amplitude-integrated EEG (aEEG) characteristics and assess regional differences.

METHODS

We investigated 40 preterm infants (postmenstrual age, PMA: range 27-37 weeks) with normal follow-up at 24 months of age, at a median postnatal age of 8 days using 4-h EEG recordings according to the international 10-20 system reduced montage. Nine (3 transverse and 6 longitudinal) channels were selected and converted to aEEG registrations. For each aEEG registration, lower margin amplitude (LMA), upper margin amplitude (UMA) and bandwidth (UMA-LMA) were calculated.

RESULTS

In all channels PMA and LMA showed strong positive correlations. Below 32 weeks of PMA, LMA was ≤5μV. Linear regression analysis showed a maximum LMA difference between channels of approximately 2 and 1μV at 27 and 37 weeks of PMA, respectively. The lowest are LMA values in the occipital channel and the highest values are in centro-occipital channels. In the frontal, centro-temporal and centro-occipital channels, UMA and bandwidth changed with PMA. No differences in LMA, UMA and bandwidth were found between hemispheres. Skewness of LMA values strongly correlated with PMA, positive skewness indicating an immature brain (PMA≤32 weeks) and negative skewness a maturing (PMA>32 weeks) brain.

CONCLUSIONS

We detected symmetric increase of aEEG characteristics, indicating symmetric brain maturation of the left and right hemispheres. Our findings demonstrate the clinical potential of computer-assisted analyses of aEEG recordings in detecting maturational features which are not readily identified visually. This may provide an objective and reproducible method for assessing brain maturation and long-term prognosis.

Reference values for amplitude-integrated EEGs in infants from preterm to 3.5 months of age

OBJECTIVES

Amplitude-integrated electroencephalogram (aEEG) is a valuable tool for the continuous evaluation of functional brain maturation in infants. The amplitudes of the upper and lower margins of aEEGs are postulated to change with maturation and correlate with postmenstrual age (PMA). In this study we aimed to establish reliable reference values of aEEG amplitudes, which provide quantitative guidelines for assessing brain maturation as indicated by aEEG results in neonates and young infants.

METHODS

aEEGs from healthy infants (n = 274) with PMAs that ranged from 30 to 55 weeks were divided into 10 groups according to their PMAs. Two 5-minute segments were selected from each aEEG and were used to automatically calculate the upper and lower margins and bandwidths of the aEEG tracings.

RESULTS

Interobserver agreement was achieved with an overall correlation of 0.99. The upper and lower margins of the aEEGs in both active and quiet sleep clearly rose in infants after the neonatal period. The bandwidth defined as the graphic distance decreased almost monotonically throughout the PMA range from 30 to 55 weeks. The lower margin of the aEEG was positively correlated with PMA, with a larger rank correlation coefficient during quiet sleep (r = 0.89) than during active sleep (r = 0.49).

CONCLUSIONS

Reference values of aEEG amplitudes were obtained for infants with a wide range of PMAs and constituted the basis for the quantitative assessment of aEEG changes with maturation in neonates and young infants. The normative amplitudes of aEEG margins, especially of the lower margin in quiet sleep, are recommended as a source of reference data for the identification of potentially abnormal aEEG results.

Electrode challenges in amplitude-integrated electroencephalography (aEEG): research application of a novel noninvasive measure of brain function in preterm infants

Continuous real-time brain function monitoring of preterm infants offers a novel way to evaluate neurological development in neonatal intensive care. Direct measurement of brain function is difficult and complicated by vulnerabilities of the preterm infant population. This study illustrates the feasibility of using noninvasive hydrogel electrodes with amplitude-integrated electroencephalography (aEEG) as a simplified brain monitor in preterm infants. This article presents a systematic exploration of factors influencing the accuracy of aEEG measurement, especially skin preparation procedures and skin condition after electrode placement. The authors conducted aEEG recordings on 16 medically stable preterm infants at 31-36 weeks postmenstrual age in the neonatal intensive care unit between feedings and caregiving for approximately 3 hr. The authors systematically performed several strategies to improve electrode placement procedures and reduce skin impedance, including (a) examination of possible influences of environmental electrical equipment, (b) comparison of different hydrogel electrode types, (c) modification of skin preparation procedures, and (d) assessment of impacts of different skin conditions. The authors achieved improvements in the impedance value, length of uninterrupted recording, and percentage of the recording duration with measured impedance <20 kΩ (recommended acceptable limit). There was no report of skin irritation during or after the recording. The aEEG measurement at the bedside using hydrogel electrodes is noninvasive and feasible for reliable brain monitoring in preterm infants. This study demonstrated the importance of establishing systematic methods to ensure the accuracy and feasibility of physiologic measurements for nurse researchers.

Using amplitude-integrated EEG in neonatal intensive care

The implementation of amplitude-integrated electroencephalography (aEEG) has enhanced the neurological monitoring of critically ill infants. Limited channel leads are applied to the patient and data are displayed in a semilogarithmic, time-compressed scale. Several classifications are currently in use to describe patient tracings, incorporating voltage criteria, pattern recognition, cyclicity, and the presence or absence of seizures. In term neonates, aEEG has been used to determine the prognosis and treatment for those affected by hypoxic-ischemic encephalopathy, seizures, meningitis and even congenital heart disease. Its application as inclusion criteria for therapeutic hypothermia remains controversial. In preterm infants, normative values and patterns corresponding to gestational age are being established. As these standards emerge, the predictive value of aEEG increases, especially in the setting of preterm brain injury and intraventricular hemorrhage. The sensitivity and specificity of aEEG are enhanced by the display of a simultaneous raw EEG, which aids interpretation. Caution must be taken when using and interpreting this tool in conjunction with certain medications and in the setting of less experienced staff. Continuing efforts at developing software that can aid seizure detection and background classification will enhance the bedside utility of this tool.

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.

Cerebral hypoxic ischemia at different cerebral oxygen saturations in piglets: amplitude-integrated EEG study

OBJECTIVE

the objective of present paper was to study the amplitude-integrated EEG (aEEG) in hypoxic ischemic (HI) animal models and to test the reliability of aEEG method when used to monitor cerebral injuries.

METHOD

HI animal models were constructed and classified into mild, moderate and severe cerebral oxygen saturation groups according to regional oxygen saturation (rSO(2)) in brains. Then aEEG waveforms were obtained from raw EEG data using digital signal processing.

RESULT

aEEG reflected cerebral functions consistently and accurately at different cerebral rSO(2) levels. aEEG waveforms rarely changed in the group of mild HI; they dropped but recovered in moderate HI group; and aEEG maintained very low after HI in the cases when severe HI happened.

CONCLUSION

aEEG method could monitor cerebral functions directly, accurately and consistently. It is a reliable tool to continuously evaluate cerebral injuries.

Development of amplitude-integrated electroencephalography and interburst interval in the rat

Continuous monitoring of electrocortical brain activity with amplitude-integrated electroencephalography (aEEG) is important in neonatology. aEEG is affected by, for example, maturity, encephalopathy, and drugs. Neonatal research uses rat pups of different ages. Postnatal day (P) 7 rats are suggested to be equivalent neurodevelopmentally to near-term infants. We hypothesized that electroencephalography (EEG) and aEEG in P1-P21 rats follow the same developmental pattern with respect to background activity and the longest interburst interval (IBI) as that seen in infants from 23-wk gestational age (GA) to post-term. We examined aEEG and EEG on 49, unsedated rat pups with two clinical monitors. aEEG traces were analyzed for lower and upper margin amplitude, bandwidth and the five longest IBI in each trace were measured from the raw EEG. The median longest IBI decreased linearly with age by 5.24 s/d on average. The lower border of the aEEG trace was <5 microV until P7 and rose exponentially reaching 10 microV by P12. This correlated strongly with the decrease in IBI; both reflect increased continuity of brain activity with postnatal age. Based on aEEG trace analysis, the rat aEEG pattern at P1 corresponds to human aEEG at 23-wk gestation; P7 corresponds to 30-32 wk and P10 to 40-42 wk.

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.

Influence of antiepileptic drugs on amplitude-integrated electroencephalography

Amplitude-integrated electroencephalography monitors different aspects of cerebral function in neonatal intensive care units. To examine the influence of various antiepileptic drugs on the background patterns and voltage of amplitude-integrated electroencephalography recordings, we screened 191 tracing segments originating from 77 newborns treated with antiepileptic drugs. The influences of lorazepam, diazepam, and phenobarbital given as bolus doses, and midazolam and lidocaine given in continuous infusion, were examined. Voltages and patterns before and after drug administration were assessed. Time taken to return to previous voltage was assessed in clinically significant cases. Chi-square and Wilcoxon tests were used for statistical analyses. Significant changes were evident after lorazepam, diazepam, phenobarbital, and midazolam administration. Depending on the voltage-assessment method, a clinically significant depression of the lower voltage border occurred in 25-35% of tracings, and of the upper border in 16-32%. In 12% of tracings, change to a worse pattern was noted. The average time for recovery to predrug administration voltage was 2.5 hours (range, 15 minutes to 15 hours). Changes in amplitude-integrated electroencephalography tracings occur after antiepileptic drugs are infused. These changes include deterioration of pattern and depression of voltage that may persist for a considerable period. The potential depressing effects of these drugs should be taken into consideration when assessing amplitude-integrated electroencephalogram tracings.

Characteristics of amplitude-integrated electroencephalogram in premature infants

The aim of this study is to evaluate and characterize amplitude-integrated electroencephalogram tracings in preterm infants at varying gestational ages. Eighty-six amplitude-integrated electroencephalogram traces (1.5-9 hours in duration each) were recorded in 32 preterm infants (24-41 weeks of postconception age) during the study period (July 1, 2001, through August 31, 2002). A stepwise rather than gradual progression was detected, with the first step at 24 to 30 weeks, the second at 31 to 34 weeks, and the third at 35 to 41 weeks. The cyclic pattern amplitude-integrated electroencephalogram typical of healthy full-term infants was not detected in the first step, which was marked by a very low baseline and a wide continuous band width of up to 98.5 microV, with a mean of 74.2 microV (SD = 23.3). The first appearance of cycles was in the second group (31-34 weeks), with a mean intercycle band width of 38.3 microV (SD = 26.3) and a cycle band width of 51 microV (SD = 18). The third step (35-41 weeks) differed from the second, having a mean intercycle band width of 16 microV (SD = 3.5; P < or = .001), with quite a similar cycle band width of 43.8 microV (SD = 19.2). The number of cycles per hour increased from a mean of 0.44 (SD = 0.33) per hour to 0.58 (SD = 0.25) per hour in the second and third steps, respectively (P < or = .001). Amplitude-integrated electroencephalogram is a feasible and reliable brain-monitoring tool in healthy preterm infants. Its features are age dependency and stepwise progression. Its real-time clinical significance and prognostic value in healthy and sick preterm infants are yet to be determined.

Continuous brain-function monitoring: state of the art in clinical practice

Continuous electroencephalographic (EEG) monitoring gives direct information on brain function in newborn infants needing intensive care. To improve the possibilities of long-term monitoring, the EEG is time-compressed and recorded with a reduced number of electrodes. A trend measure of the EEG, the amplitude-integrated EEG (aEEG), has proved capable of giving relevant information in newborn infants of differing levels of maturity. The electrocortical background activity gives information on the level of brain activity, which is associated with outcome in both term asphyxiated infants and in preterm infants. However, the background activity is also affected by several medications, and this must be considered when interpreting the aEEG trace. The aEEG also reveals subclinical epileptic seizure activity, and can be used for evaluation of anti-epileptic treatment. The aEEG should be used as a complement to the standard EEG, and close collaboration between neonatologists and clinical neurophysiologists is necessary for optimal performance of EEG monitoring.

Continuous electroencephalography monitoring of the preterm infant

Continuous electroencephalography (EEG) monitoring provides clinically relevant information in preterm infants. Acute changes during development of intraventricular hemorrhage and white matter injury are associated with EEG and amplitude-integrated EEG (aEEG) deterioration. The early EEG background is also correlated with outcome in preterm infants, although other problems associated with prematurity may influence the long-term prognosis. The limitations of EEG monitoring should be well-understood by users and the continuous EEG monitor should be used as a complement to the standard EEG.

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.

Excitatory amino acid release and electrocortical brain activity after hypoxemia in near-term lambs

BACKGROUND

Energy failure due to insufficient cerebral O(2)-supply leads to excess accumulation of calcium ions in presynaptic neurons, followed by excess release of excitatory amino acids (EAAs), which are potent neurotoxins, into the synaptic cleft.

AIM

The aim of the present study was to determine whether extracellular EAAs release after prolonged hypoxemia affects electrocortical brain activity (ECBA), as a measure of brain cell function, in near-term born lambs.

METHODS

Ten near-term lambs (term: 147 days) were delivered at 131 days of gestation. After a stabilization period, prolonged hypoxemia (FiO(2): 0.10; duration 2.5h) was induced. Mean values of physiologic variables, including ECBA, were calculated over the last 3 min of normoxemia as well as of hypoxemia. Cerebral arterial and venous blood gases were determined at the end of the normoxemic and hypoxemic periods. Cerebrospinal fluid (CSF) was obtained at the end of the hypoxemic period. CSF from six normoxemic sibs was used for comparison. HPLC was used to measure EAAs in the CSF.

RESULTS

During hypoxemia, aspartate and glutamate concentration increased significantly (4.8 and 6.0 times, respectively), while asparagine and glutamine did not. ECBA decreased to 30% of the normoxemic value. Glutamate was significantly higher in lambs with a flat cerebral function monitor (CFM) tracing than in lambs with a burst-suppression pattern.

CONCLUSIONS

After prolonged hypoxemia aspartate and glutamate accumulated excessively in the CSF of near-term born lambs. Especially glutamate concentrations in CSF were related to the decline in brain cell function.

Amplitude-integrated EEG in preterm infants: maturation of background pattern and amplitude voltage with postmenstrual age and gestational age

OBJECTIVE

Amplitude-integrated electroencephalogram (aEEG) is a single channel EEG recorded from two parietal electrodes. The objective of this study was to test the hypothesis that aEEG maturation follows postmenstrual age (PMA) irrespective of gestational age (GA).

METHODS

We recruited inborn infants with a GA <33 weeks and without evidence of neurologic anomaly. Serial aEEG recordings were assessed for: presence of continuous activity and mature sleep-wake cycling (SWC); low base voltage (V), that is, the lowest amplitude margin; high base V, that is, the most common amplitude margin; upper high V, that is, upper margin during highest activity; and span, that is, the difference between upper high and simultaneous high base V. Statistical analysis included logistic regression and repeated measures analysis of variance.

RESULTS

We obtained 119 aEEG recordings in 31 preterm infants (GA 25 to 32 weeks; birth weight 600 to 1704 g, PMA 25 to 35 weeks). The frequency of mature SWC increased with PMA independent of GA, while the frequency of continuity increased with PMA and was higher in extremely preterm infants after correcting for PMA. Low base and high base V increased with PMA, while span and upper high V significantly decreased with PMA. In addition, high base V was higher in extremely preterm infants after correcting for PMA.

CONCLUSIONS

In preterm infants aEEG matures predominantly with PMA. Our data suggest that some aspects of aEEG maturation are enhanced, rather than inhibited by extremely preterm birth. These data suggest that aEEG in preterm infants may need to be analyzed by comparing results with standards of similar PMA and GA.

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.

Cerebral O2 supply thresholds for the preservation of electrocortical brain activity during hypotension in near-term-born lambs

The fetal brain develops rapidly during the last trimester of pregnancy. Therefore, the brain of infants who are born preterm is vulnerable to changes in oxygen and nutrient supply in the neonatal period. The objective was to determine the effect of gestational age (GA) on the cerebral O2 supply threshold level for preservation of brain function during hypotension in near-term-born lambs. Lambs were delivered at 141 or 127 d of gestation. Hypotension was induced by stepwise withdrawal of blood. Mean arterial blood pressure (MABP) baseline levels were 63.2 (6.4) in 141-d and 54.4 (15.5) mm Hg in 127-d lambs. The MABP threshold below which MABP and blood flow in the left carotid artery were linearly related was 36.1 (13.1) mm Hg in 141-d lambs. In 127-d lambs, MABP and blood flow in the left carotid artery were linearly related over the whole range of recorded MABP values. Electrocortical brain activity (ECBA) was used as a measure of brain function. Thresholds of MABP for maintenance of ECBA were reached at, respectively, 31.6% (4.9%) of baseline in 141-d and 61.9% (13.0%) of baseline MABP in 127-d lambs. However, thresholds of cerebral O2 supply for maintenance of ECBA were similar in both GA groups. We conclude that thresholds of cerebral O2 supply for maintenance of brain cell function are independent of GA but are reached at higher MABP levels in 127-d than in 141-d lambs and therefore places the sick preterm infant easily at risk for ischemic cerebral injury.

Purine and pyrimidine metabolism and electrocortical brain activity during hypoxemia in near-term lambs

Insufficient cerebral O(2) supply leads to brain cell damage and loss of brain cell function. The relationship between the severity of hypoxemic brain cell damage and the loss of electrocortical brain activity (ECBA), as measure of brain cell function, is not yet fully elucidated in near-term newborns. We hypothesized that there is a strong relationship between cerebral purine and pyrimidine metabolism, as measures of brain cell damage, and brain cell function during hypoxemia. Nine near-term lambs (term, 147 d) were delivered at 131 (range, 120-141) d of gestation. After a stabilization period, prolonged hypoxemia (fraction of inspired oxygen, 0.10; duration, 2.5 h) was induced. Mean values of carotid artery blood flow, as a measure of cerebral blood flow, and ECBA were calculated over the last 3 min of hypoxemia. At the end of the hypoxemic period, cerebral arterial and venous blood gases were determined and CSF was obtained. CSF from 11 normoxemic siblings was used for baseline values. HPLC was used to determine purine and pyrimidine metabolites in CSF, as measures of brain cell damage. Concentrations of purine and pyrimidine metabolites were significantly higher in hypoxemic lambs than in their siblings, whereas ECBA was lower in hypoxemic lambs. Significant negative linear relationships were found between purine and pyrimidine metabolite concentrations and, respectively, cerebral O(2) supply, cerebral O(2) consumption, and ECBA. We conclude that brain cell function is related to concentrations of purine and pyrimidine metabolites in the CSF. Reduction of ECBA indeed reflects the measure of brain damage due to hypoxemia in near-term newborn lambs.

Reference values for amplitude-integrated electroencephalographic activity in preterm infants younger than 30 weeks' gestational age

OBJECTIVE

To prospectively investigate the development of amplitude-integrated electroencephalographic (aEEG) activity during the first 2 weeks of life in neurologically normal and clinically stable preterm infants <30 weeks' gestational age (GA).

PATIENTS AND METHODS

Infants with a GA of <30 weeks admitted to the neonatal intensive care unit of the Vienna University Children's Hospital (Vienna, Austria) were studied prospectively by using aEEG and cranial ultrasound. Clinically stable infants without clinical or sonographic evidence of neurologic abnormalities were eligible for inclusion in the reference group. The distribution of 3 background aEEG activity patterns (discontinuous low-voltage, discontinuous high-voltage, and continuous), presence of sleep-wake cycles, and number of bursts per hour in the reference group were determined by visual analysis.

RESULTS

Seventy-five infants (median GA: 27 weeks; range: 23-29 weeks) were eligible for inclusion in the reference group and had aEEG recordings during the first 2 weeks of life available. Analysis of aEEG background activity showed that with higher GA the relative amount of continuous activity increased while discontinuous patterns decreased. The number of bursts per hour decreased with increasing GA. Cyclical changes in aEEG background activity resembling early sleep-wake cycles were observed in all infants.

CONCLUSIONS

Normal values for aEEG background activity were determined in preterm infants <30 weeks' GA. Clinically stable and neurologically normal preterm infants exhibit at least 2 different patterns of aEEG activity. There is a correlation between the GA and the relative duration of continuous aEEG activity.

Cerebral function monitoring: a new scoring system for the evaluation of brain maturation in neonates

OBJECTIVE

Cerebral function monitoring (CFM), using compressed single-channel amplitude-integrated electroencephalogram recorded from 2 biparietal electrodes, has been shown previously to be a simple bedside tool for monitoring neonatal central nervous system (CNS) status. As the pattern of the CFM changes with gestational age, the technique can be used to assess brain maturation in premature infants. We have developed a new scoring system for the interpretation of neonatal CFM recordings. The objective of this study was to evaluate CFM tracings at increasing gestational and postnatal ages to develop a scoring system to quantify CFM pattern changes.

METHODS

Term and preterm neonates were studied with CFM at 12 to 24 hours of life, 48 to 72 hours of life, and then weekly or biweekly until hospital discharge. Each study comprised 8 to 24 hours of continuous CFM recording. CFM recordings were evaluated using the scoring system for record continuity, presence of cyclic changes in electrical activity, degree of voltage amplitude depression, and bandwidth. Each variable was scored for each recording. All variables were summed to yield a total score (minimum 0, maximum 13). Total scores were correlated with gestational and postconceptional ages.

RESULTS

Thirty infants were studied with gestational ages at birth that ranged from 24 to 39 weeks and birth weights that varied between 450 and 3850 g. A total of 146 CFM tracings were analyzed. With advancing gestational and postconceptional age, scores for each variable as well as total scores progressively increased with CNS maturation. The highest scores were attained at 35 to 36 weeks' postconceptional age, which corresponded to previously reported subjective observations performed by visual description of CFM patterns. Of the 4 component variables that we analyzed, the most sensitive indicators of CNS maturity were 1) the presence of a cycling pattern, 2) the continuity of the record pattern, and 3) the CFM recording bandwidth.

CONCLUSIONS

Our proposed scoring system may be a valuable tool to quantify changes during CFM more objectively, reflecting variations in CNS activity in newborn infants and allowing for better statistical comparisons between amplitude-integrated electroencephalogram tracings from different patients as well as from the same patient at different points of time.

Electrocortical brain activity, cerebral haemodynamics and oxygenation during progressive hypotension in newborn piglets

OBJECTIVES

To investigate the relationships between systemic and cerebral haemodynamics and oxygenation, and electroencephalogram (EEG) amplitude and frequency analysis studied by the cerebral function analyzing monitor (CFAM) during progressive hypovolemic hypotension.

METHODS

Six piglets of 1 week of age, weighing 1.9-3.4 kg were mechanically ventilated under 1-1.5% halothane anaesthesia. After 1 h stabilization, blood was withdrawn in aliquots of 10 ml/kg over 15 min up to a total of 40-60 ml/kg. Arterial oxygenation was maintained at normal levels. Thereafter, the total blood volume previously withdrawn, was reinfused. Changes in near infrared spectroscopy (NIRS) parameters [cerebral oxidized cytochrome aa3 (Cytaa3), cerebral blood volume (CBV) or total haemoglobin (tHb: oxy- + deoxyhaemoglobin)], carotid blood flow (Q(car)), maximal EEG amplitude and EEG frequency percentages were analyzed continuously.

RESULTS

The EEG amplitude remained stable until the mean arterial blood pressure (MAP), Q(car) and tHb dropped below 30 mmHg (41% of baseline), 20 ml/min (33% of baseline) and 82% of baseline, respectively. Delta (delta) wave frequency percentage of the CFAM increased significantly at MAP below 30 mm Hg. EEG amplitude remained depressed after blood reinfusion and haemodynamic recovery. Cytaa3 changes were not statistically significant, reflecting sufficient neuronal oxygenation.

CONCLUSION

Our results show that electrocortical function is affected only by profound systemic hypotension. This occurred at a higher level of cerebral oxygen delivery than the level associated with neuronal hypoxia and secondary cell damage.

The Maastricht Cerebral Monitor (MCM) for the neonatal intensive care unit

Although long-term monitoring of cerebral activity can be important in neonatal intensive care, the complexity of multi-channel EEG makes it less suitable for this purpose. In the past, a cerebral function monitor (CFM) was developed that analyses EEG. The output parameter of the CFM is a semi-logarithmic amplitude distribution resulting from the amplification, bandpass filtering, compression, rectification and smoothing of the single-channel EEG. Drawbacks of the CFM include its inflexibility and limited single-channel processing capacity and its lack of functionality for data storage, review or re-analysis. Modern computers are powerful enough that a system can be built which does not have these drawbacks. We have developed such a system: the Maastricht Cerebral Monitor (MCM). The MCM is a flexible system that not only overcomes the CFM drawbacks but also provides advanced signal analysis. It was developed with a software system (Poly) for acquisition, high quality real-time display, on-line analysis and storage of physiological signals. The MCM processes three EEG signals in the amplitude and frequency domains. Other parameters provided by the MCM are asymmetry of absolute frequency powers, percentage suppression, mean and 90% spectral edge frequency. Electrode impedance is recorded as a measure of quality of the recording.

Neurological assessment of the preterm infant

Coinciding with improved overall management of the very preterm infant, more techniques have become available to assess the neurological well-being of these high-risk infants. An overview is given of the different techniques which are now used in many neonatal intensive care units, and their value in predicting neurodevelopmental outcome is discussed. Attention is mainly focused on cranial ultrasound, electroencephalography and the different evoked potential modalities.

Cerebral and ventilatory depression during hypoxia in anaesthetized newborn guinea-pigs

The effects of hypoxia on ventilation and cerebral activity were studied in urethane-anaesthetized newborn guinea-pigs. Ventilation was measured by a pneumotachograph, and cerebral activity by a cerebral function monitor (CFM). All animals were subjected to either 9% O2 or 6% O2 in N2 for 10 minutes or until apnoea occurred. Hypoxia produced a biphasic response in ventilation, that is, an increase followed by a decrease. The initial increase was attributed to the elevation of the respiratory rate, whereas the tidal volume showed a pure decline. The respiratory rate reached its peak at 3 minutes of hypoxia (170 +/- 12% during 9% O2 and 169 +/- 12% during 6% O2). Cerebral activity during both 9 and 6% O2 breathing showed a small increase followed by a decrease. In the group subjected to 9% O2 the maximum CFM activity increased to 114 +/- 8% of the control level and the minimum activity increased to 113 +/- 7%, while in the group subjected to 6% O2 the maximum CFM activity increased to 104 +/- 5% and the minimum CFM activity to 101 +/- 3%. The depression of CFM activity was more pronounced with 6% O2 than with 9% O2. Regression analysis showed a linear correlation between ventilation and cerebral activity during both 9 and 6% O2 breathing. The results suggest that hypoxic ventilatory depression may be the consequence of cerebral depression produced by acute severe hypoxia.

Maturation of electroretinograms and visual evoked potentials in preterm infants

Electroretinograms (ERGs) and visual evoked potentials (VEPs) to flash stimulation were recorded from 51 infants (gestational age 26 to 42 weeks; post-conceptional age (PCA) 31 to 47 weeks) to give cross-sectional data on the maturation of these responses. Sequential recordings were taken from a separate group of 24 preterm infants (gestational age 28 to 33 weeks) to give longitudinal data. There was a significant decrease in ERG a-wave latency and increase in a-b amplitude with increasing PCA in both groups. For the VEPs there was a significant decrease in latency of the early negative component (N1) and the major positive component (P2). Comparison between recordings made on preterm infants with those from term infants at an equivalent PCA suggested faster maturation of VEPs in the extra-uterine environment, but no difference in maturation of the ERG.

Cerebral function monitoring: a method of predicting outcome in term neonates after severe perinatal asphyxia

The cerebral function monitor (CFM), a simplified one-channel EEG monitor, was evaluated in predicting outcome after severe perinatal asphyxia in 38 term infants. Survivors were followed until 1.5-2.5 years of age. All those 17 infants who survived without major neurological handicap showed continuous activity on the CFM trace during the first and/or second day of life. Twenty of the 21 infants who either died or developed severe neurological damage had burst suppression or paroxysmal activity on the first or second day of life. Thus cerebral function monitoring can be a valuable tool in predicting prognosis for infants with severe perinatal asphyxia.

Comparison between tape-recorded and amplitude-integrated EEG monitoring in sick newborn infants

In 15 ill newborn infants a comparison between long-term multichannel and single-channel recordings of simultaneously tape-recorded (Medilog system) and amplitude-integrated EEG (Cerebral Function Monitor) was made. There was good agreement between the main type of background activity diagnosed with the tape-recorded and the amplitude-integrated EEG for all recordings. Two infants had repetitive subclinical and subtle seizure activity, lasting for several hours, which was detected by both techniques. Short, single seizures were diagnosed in the recordings of nine infants. When a single electrographic seizure appeared in an otherwise stable recording, it was identified by both the tape-recorded and the amplitude-integrated EEG. Very short (5-30 s) seizure patterns, which were diagnosed with the tape-recorded EEG, were not identified in the cerebral function monitor recordings. In the single-channel recordings of both the EEG and the cerebral function monitor there were, on some occasions, difficulties in distinguishing single seizures from interference due to external artefacts. In the multichannel recordings the diagnosis of seizure patterns was facilitated by comparison with the other channels. Both the Medilog EEG and the cerebral function monitor are feasible techniques for following cerebral electrical activity in sick neonates, although neither technique is specifically constructed for this purpose. For clinical use in the neonatal intensive care unit the advantage with the cerebral function monitor is the immediately available recording. The tape-recorded EEG offers possibilities of more channels and a higher reliability when diagnosing short subclinical seizures, however, only after offline analysis.

Cerebral complications detected by EEG-monitoring during neonatal intensive care

The report describes the clinical use and value of continuous EEG-monitoring during different clinical circumstances that are not usually related to changes in EEG. Three infants with pneumothorax, hypoglycaemia, and severe hyaline membrane, respectively, are presented.