Amplitude-integrated electroencephalographic activity is suppressed in preterm infants with high scores on illness severity☆
Introduction
Neonatal intensive care involves continuous monitoring of vital signs such as heart rate, arterial oxygen saturation, and blood pressure. Means of assessing the neurological condition of an infant admitted to a neonatal intensive care unit (NICU) are limited. The standard diagnostic tools include clinical observations of general movements and cerebral ultra-sonography [1], [2]. Another method of assessing brain function is to measure electro-cerebral activity by means of an electro-encephalogram (EEG). It provides information about patterns of cerebral activity, such as the different stages of sleep and wakefulness, and reveals pathological processes like seizures [3].
In our NICU we use a cerebral function monitor (CFM) to continuously monitor electro-cerebral activity. The CFM displays a single channel EEG recorded through bi-parietal electrodes. It provides a simplified, time-compressed EEG, a so-called amplitude-integrated EEG (aEEG). aEEGs are interpreted by pattern recognition, which is, to some extent, a subjective method [4]. A previous EEG study of preterm infants demonstrated that electro-cerebral activity varies with gestational age [5]. With increasing gestational age the background activity changes from discontinuous normal voltage to continuous normal voltage and eventually to continuous normal voltage with sleep–wake cycling. Young preterm infants have profoundly discontinuous background patterns on both EEG and aEEG, often appearing as burst suppression [6], [7], [8]. In preterm infants aEEGs are influenced by both gestational age and postnatal age [9]. Based on the features of pattern recognition (continuity, cycling, lower border, and bandwidth of the aEEG amplitude) the so-called Burdjalov score can be calculated [8]. This score increases with increasing gestational age. By using a digital device that computes the centiles of the aEEG amplitudes, the aEEGs can be quantified in more detail.
In full term infants aEEG traces are very effective in predicting neurological outcome at an early stage following perinatal asphyxia [10], [11], [12], [13]. Low voltage traces predict an impaired neurological outcome. Some studies indicated that aEEGs may be helpful in predicting neurological outcome in high-risk preterms with intraventricular haemorrhage (IVH) or post-haemorrhagic hydrocephalus [14], [15], [16]. It is unknown whether the severity of illness in preterm infants influences their aEEGs. Illness severity can be assessed by the score for neonatal acute physiology, the SNAP-II score [17].
Our first aim was to investigate whether assessing the aEEG amplitudes by calculating amplitude centiles was consistent with calculation of the Burdjalov score. Our second aim was to investigate whether the aEEGs of preterm infants were influenced by the SNAP-II scores during the first five days of life. We hypothesised that the aEEGs were more discontinuous in case of high SNAP-II scores. In addition, we investigated which individual items of the SNAP-II score and the 5 min Apgar score influenced the aEEGs.
Section snippets
Methods
This prospective observational study was performed at the NICU of the University Medical Center Groningen in the Netherlands from February 2006 to February 2007. All preterm infants with a gestational age of 26–32 weeks admitted on the first day of life were eligible for inclusion. Exclusion criteria were IVH exceeding grade II according to Volpe [18], chromosomal abnormalities, and severe congenital malformations. Infants with IVH exceeding grade II were excluded because electro cerebral
Study Group
Data were collected on 43 infants of whom five were excluded: two due to large IVHs, and for three the data on the illness severity model were incomplete. The study cohort therefore consisted of 38 infants. Their gestational ages ranged from 26 to 31.9 weeks (mean 29.7 weeks, SD 1.4). We obtained 190 recordings. Artefacts were present in 49 recordings. The remaining 151 reliable recordings had a mean duration of 130 min. Surfactant was administered to 22 infants. In 15 infants the surfactant was
Discussion
This study demonstrated that calculating aEEG amplitude centiles was a viable method for assessing aEEGs. Since the majority of preterm infants had a discontinuous background pattern at the start of aEEG recording, we assessed the aEEGs by pattern recognition, using the score published by Burdjalov et al. [8]. In previous studies, aEEG patterns were only assessed by pattern recognition: analysing the lower margin of the amplitude, the appearance of continuity, and the presence of cycling of the
Conclusions
The assessment of aEEGs by calculating amplitude centiles proved to be a valid method. Electro-cerebral activity of preterm infants was influenced negatively by severe illness. This effect is the most apparent on the first day after birth. We found that two aspects of severe illness, i.e. a low 5 min Apgar score, and low blood pressure had a suppressive effect on aEEG activity. Finally, electro-cerebral activity was clearly affected by gestational age.
Acknowledgements
This study was part of the research programme of the postgraduate school for Behavioral and Cognitive Neurosciences, University of Groningen, the Netherlands. We greatly acknowledge the help of Dr Titia Brantsma-van Wulfften Palthe in Utrecht for correcting the English.
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Ethical statement. The study was approved by the review board of University Medical Center Groningen.
The authors have nothing to disclose.