163 Qualitative Analysis of Artefacts on Raw EEG and the Influence on aEEG Classification

Abstract

Background: In infants with neonatal encephalopathy (NE) the amplitude-integrated electroencephalogram (aEEG) has been used to both predict outcome and select infants for neuroprotection, based on a simple aEEG classification (1). Recently, digital aEEG monitors, which record and store a raw single channel EEG in addition to aEEG, have been developed.Aims: To assess (i) the source of aEEG artefacts; and (ii) determine how the underlying raw EEG modulates the aEEG in a representative group of infants with NE.Methods: 50 hours of aEEG and the underlying raw EEG (CFM 6000 Olympic Medical, USA) from 5 term infants with NE were retrospectively analysed and inspected for the source and duration of artefacts. Movement artefacts were defined as sudden alterations in the aEEG trace or rapid irregular low voltage distortion of the EEG without discernible EEG characteristics (Fig.1). Electrical artefacts were defined if electrocardiogram interference was observed on the raw EEG (Fig.2).Results: Raw EEG artefacts were observed during 21% of the recording period. 76% of the artefacts were due to movement (muscle shivering, gasping or ventilation) and 24% of the artefacts were due to electrical interference. Sudden movement artefacts could be mistaken for seizures; repetitive movements caused either widening of the trace or raised the lower margin of the aEEG trace. Electrical interference from the ECG raised the lower margin of the aEEG trace.Conclusion: aEEG artefacts were common during this representative period. Without knowledge of the raw underlying EEG, both movement and electrical artefacts may lead to misclassification of the aEEG. It is essential to scrutinise the underlying raw EEG to detect artefacts; this should improve the accuracy of aEEG classification and enhance the use of aEEG for determining prognosis in NE. 1. alNaqueeb et al., Pediatrics 1999;103:1263–1271 Fig.1:Sudden alteration of aEEG trace (arrow), movement artefact seen on EEG Fig.2:Alteration of aEEG due to electrical interference (arrow)