This prospective pilot study of intubated and mechanically ventilated ELBW infants showed the following key findings: most infants displayed a discontinuous tracing that was briefly disrupted during surfactant and suctioning procedures; most importantly, we observed that the aEEG low voltage burst suppression pattern was an ominous predictor, with 100% positive predictive value, for developing severe ICH.
This study focused on the description of the aEEG electrical background activity in newborn ELBW infants. Importantly, aEEG background electrical activity can easily be interpreted at the bedside by neonatologists trained in aEEG pattern recognition [7
] and may be reflective of short-term poor prognosis. We used a priori the Hellström-Westas [7
] classification system to allow for generalizability of our findings. Previous studies using a semi-quantitative description of the maturational changes in extremely preterm infants reported a progression from a mostly discontinuous low voltage pattern without sleep cycling to a more continuous pattern with the emergence of sleep wake cycles and a narrowing of the inter-cycle bandwidth [10
]. Consistent with these studies, most of our ELBW newborns had discontinuous tracings, while some also had a burst suppression pattern with inactive lower band tracing.
Most infants had increased electrical excitability on aEEG during surfactant administration and suctioning. We previously reported [8
] during both the second dose of beractant and during tracheal suctioning in very low birth weight infants a significant increase in middle cerebral artery CBF velocity. This CBF velocity increase has been described previously to be predominantly related to changes in PaCO2
and not to changes in mean arterial blood pressure, i.e., most infants presumably had intact cerebral auto regulation [9
]. The current study further supports this concept, as evidenced by the absence of electrocortical depression that has been reported in other studies during surfactant treatment [16
]. These latter surfactant studies where poractant was used have reported 10–20 minute decreases in electrocortical activity and a simultaneous decrease in mean arterial blood pressure. We speculate lack of electro cortical depression in our current study was concordant with the observed unchanged stable mean arterial blood pressure during beractant administration. Discrepancies between our results compared to others may be related to the use of beractant vs. poractant, differences in surfactant administration protocols, as well as differences in patient populations being studied.
The third and most important finding in the current study relates to the usefulness of the aEEG recording, specifically the presence of the low voltage burst suppression pattern, to detect ongoing or developing brain injury in newborn ELBW infants. Others [19
] have correlated aEEG abnormalities with structural brain damage including, hydrocephalus and IVH. Prognostic aEEG factors such as the number of bursts have also been shown to predict death or severe neuromotor impairment in infants with grade 3 or 4 IVH [23
]. Another factor found to be associated with IVH is the delayed recovery of low voltage background otherwise expected with increasing maturity [24
]. Depressed voltage background activities with decreased amount of continuous activity, epileptic seizures, and burst density have all been reported in infants who had large IVHs [20
]. A more recent aEEG study using both visual analysis and quantitative analysis software reported that decreased aEEG continuity (<80% continuity at 10 μv) was a strong predictor of poor short-term outcome by identifying 83% of infants who died or had severe IVH [26
]. Since this software is not generally available for clinical use, and requires offline analysis, we elected in our study to focus on simple pattern recognition using an internationally recognized classification scheme that can be widely applicable in real-time to clinical neonatologists.
Strengths of this study are: the prospective design focusing on early assessment of a previously unstudied homogeneous inborn population of newborn ELBW infants requiring surfactant treatment for respiratory distress syndrome, the serial monitoring around neonatal intensive care procedures, and the blinded interpretations of tracings in relation to occurrence of ICH by one of the authors (LC).
We acknowledge the following limitations due to our study design: small sample size in this pilot study, tracings were obtained intermittently rather than continuously, tracings were not available beyond 48 hours of life, the focus was solely on background electrical activity, and the study did not include long-term follow-up. Despite these limitations, we were able to find that low voltage discontinuous activity with burst suppression was an ominous finding predicting the occurrence of severe ICH with 100 % positive predictive value and specificity. Moreover, caution should be used in the interpretation of aEEGs in ELBW infants due to the predominance of discontinuous tracings and the transient effect of neonatal interventions as seen with suctioning and surfactant administration. The low sensitivity of a low voltage with burst suppression might be related to the interplay of complex pathophysiological changes associated with severe intracranial hemorrhage. Any acute change in cerebral perfusion or metabolism can potentially affect the continuity of aEEG, such as profound hypoglycemia, or metabolic disorders. Administration of opioids or antiepileptic especially in critically ill newborns could lead transiently to low voltage burst suppression, and has been reported following infusions of morphine, lidocaine or Phenobarbital [27
Our study suggests that finding low voltage burst suppression pattern should prompt an immediate cranial ultrasound for confirmation due to the high likelihood reported. This pattern, however, is not a necessary finding for predicting severe ICH as shown by the observed lower sensitivity, and should by no means be a replacement for scheduled routine cranial ultrasounds during the neonatal period. Rather than an alternative diagnostic tool for severe intracranial hemorrhage, we suggest that aEEG is an acceptable bedside screening device to prompt immediate medical attention, in the middle of night to the child condition. Clinical acumen about other hemodynamic changes that might be occurring can help next paradigm for decision making.
With updated development of digital equipment, new generation monitors can record variable number of channels with simultaneous EEG and aEEG, further closing the gap between the two devices. This article adds information on limitation and utility of the aEEG in extremely low birth weight infants while this technology is already making rampant use in neonatal intensive care settings.