The interpretation of the neonatal electroencephalogram consists of related phases of analysis most of which are conducted in parallel. Initially, the EEG is assessed to determine the conceptional age (CA) of the infant. In concert with this, the background activity is assessed to determine whether it is normal, and if not, to characterize the abnormal features. In addition, the determination of CA provides the basis for the understanding of the range of both diffuse and focal abnormalities that may be anticipated within each age-dependent epoch. Thus, visual analysis of the neonatal EEG begins with the recognition of the CA-dependent features characteristic of specific epochs of development. This is followed by inspection for EEG abnormalities based on an understanding of possible age-dependent findings. Taken together these aspects of visual analysis of the neonatal EEG provide the basis for the determination of CA of the infant and the assessment of the degree to which the EEG is normal.

Two additional principles of interpretation of the neonatal EEG relate to age-dependent changes over time and to findings of indeterminate significance. Typically, the EEG-determined age of the infant is given in CA—considered the age from the time of conception. The gestational age (GA) is the time from conception to the time of birth. The chronologic or legal age is the time from birth to the time of the EEG. The CA is the GA plus the legal age. A basic principle of interpretation of the neonatal EEG is that the immature brain develops at the same rate whether in utero or following delivery. Thus, the EEG recorded several weeks after an infant was born prematurely would have similar features to an EEG recorded on the first day of life of infant whose CA equaled the GA plus the legal age of the premature infant. Another important consideration is that the clinical significance of all features of the neonatal EEG has not been determined. Thus, the challenge is to differentiate the known from the unknown and focus interpretation on those aspects of the EEG for which accurate data are available.

A number of investigators have, over the years, contributed to our understanding of the normal neonatal EEG beginning with the pioneering work of the French school (1, 2, 3, 4 and 5). More recent discussions of normal neonatal electroencephalography include those by Hrachovy et al. (6), Watanabe et al. (7), Clancy et al. (8), Mizrahi et al. (9), Plouin et al. (10), Vecchierini et al. (11), and André et al. (12).

The general principles of recording the electroencephalogram in neonates are similar to those of older children and adults with some important additions and exceptions. Guidelines for the recording of the neonatal EEG have been established by the American Clinical Neurophysiology Society (13) and the International Federation of Clinical Neurophysiology (14).

Critical to the recording of neonatal EEG is a well-trained staff of electroneurodiagnostic technologists (ENDTs) with expertise in the recording of newborn and young infants. To insure maximum clinical relevance, the ENDT should obtain basic information about each neonate to be recorded including standard demographic data, description of the recording environment, documentation of reason for referral, details of the medical history, a list and timing of medications, and the specifics of the infant’s general medical condition. In addition, the technologist must consider the state of each infant and determine the best method to make the infant as comfortable as possible in order to obtain a complete recording. This may require having the infant fed, having diapers changed, adjusting room temperature and, often, just prolonging the recording until the infant becomes comforted.

The International 10-20 System of Electrode Placement has been modified for recording neonates. Typically, a minimum of nine scalp positions are utilized (F1, F2, C3, C4, CZ, T3, T4, O1, and O2). In addition, electrodes are placed at A1 and A2 and a ground electrode is placed either at mid-forehead or on a mastoid region. Since digital recordings are fundamentally referential, an additional reference electrode position may be needed (typically noncephalic), although some instruments provide a so-called “internal” reference. The F1 and F2 electrode positions are 20% of the inion-nasion distance above the nasion and 10% of the circumferential measurement from the midline. Their placement allows for the foreshortened position of the neonatal immature frontal lobes. Placement of all of the standard electrodes of the International System would result in such close spacing on the neonate’s scalp that electrode recording may overlap with redundant electrical fields. Paste, not collodion, is utilized for electrode placement.

Polygraphic measures are integral to the recording of the EEG in order to assist in characterizing sleep states, eye movements, muscle contractions, cardiac rhythms, and respiratory patterns and to assist in identification of noncephalic artifact. The polygraphic measures include the electrooculogram
(EOG), submental electromyogram (EMG), electrocardiogram (ECG), and respiratory monitors such as a strain gauge, bipolar electrodes, or pneumograph.

The recording of the neonatal EEG includes the documentation of wake/sleep cycles, the characterization of reactivity of the record to stimulation and identification of age-dependent waveforms and other features. These are best achieved utilizing a single, bipolar montage with broad coverage over the scalp. Digital recording of the neonatal EEG provides the opportunity to examine various waveforms with different montages after recordings are complete.

Instrument settings used at the onset of recording are listed in Table 9.1. The filter settings and sensitivity of the EEG channels should be the same as that for EOG in order to allow accurate comparison of waveforms to differentiate cerebral activity from that of ocular origin. Paper speed is set at 30 mm/sec for analog recordings or 10 sec/screen or “page” for digital recordings. These paper speed settings are utilized in many laboratories in the United States. However, several laboratories, particularly those with ties to the French School of Recording, utilize a slow speed: 15 mm/sec or 20 sec/“page.”

The most successful and clinically relevant neonatal EEG recordings are those in which objectives and strategies are identified prior to the beginning of each study. Advance planning is essential. The basic tasks are to obtain historical data, determine reason for referral, initiate technical recordings, examine the EEG in real time, observe the infant for clinical behaviors, record the infant in sleep and wakefulness, and attempt to provoke abnormal paroxysmal clinical events. Close observation of the infant at all times is particularly important when recording a neonatal EEG. The record should be annotated when behavioral or autonomic changes occur or when other events happen that may affect the record.

A final technical consideration relates to the duration of the neonatal EEG recording. There are two considerations: the time it may take for the infant to experience the full cycles of sleep and wakefulness, and a sufficient period of time for the infant to experience clinical or electrical events. The typical minimum duration of recording for a neonatal EEG is 1 hour. However, the recording duration is an interactive process based on clinical circumstances and the unfolding EEG.

Initial analysis includes the assessment of the degree of continuity of background activity and the degree of interhemispheric synchrony of the background activity. Further analysis consists of inspection for specific age-dependent waveforms and patterns (so-called “grapho-elements”) (Table 9.2) and the presence and character of sleep/wake cycles. In addition, there is recognition of some special waveforms and patterns that occur in the near-term or term infant that are considered developmental milestones and variations of the normal EEG.