Because of the smaller head size in children, fewer electrodes are generally used than in adult patients with whom the 10-20 system is typically used. American Clinical Neurophysiologic Society (ACNS) guidelines⁵ recommend the following placement: Fp1 and Fp2 [or Fp3 and Fp4 (Fp3 is halfway between Fp1 and F3 and Fp4 is halfway between Fp2 and F4)], C3 and C4, T3 and T4, O1 and O2, A1 and A2, and Cz. A recording utilizing at least 12 channels should be used. For EEG recording, the use of low-frequency filter of 0.3 to 0.6 Hz or time constant of 0.27 to 0.33 second is recommended. The sensitivity is usually 7 µv/mm but might need to be adjusted either higher or lower depending on the case.

In order to assess waking and sleeping states (quiet and active sleep), respiratory movements and airflow, EKG, EOG, and submental EMG are routinely recorded. This has been facilitated by the ability of some software packages to interface with typical neonatal monitoring systems allowing the accurate acquisition of respiratory, pulse oximetry, and heart rate data. Besides recording EEG, additional channels are dedicated to respiratory movements by abdominal and/or thoracic strain gauges or impedance pneumogram and airflow by thermistors/thermocouples, EKG, EOG, and submental EMG. For EOG recording, low-frequency filter of 0.3 to 0.6 Hz would be adequate. For EMG recording, low-filter setting of 5 Hz and high filter of 70 Hz, and sensitivity of 3 µv/mm are used.

Commonly used montages (as recommended by ACNS) are shown in Table 16-1.⁵ Recording montages should routinely include the vertex (Cz) electrode because significant EEG patterns characteristic for this age group (positive vertex sharp waves, negative vertex sharp waves, and electrographic seizures) may be detected only from this region. Unlike in older children and adults, multiple reviewing montages are typically not used with readers typically relying on a comprehensive bipolar montage with the addition of the aforementioned other leads.

Besides gathering routine information for EEG recording (history, reason for referral, medication, state of consciousness, etc.),
it is imperative to note the gestational age (GA) (the time elapsed between the first day of the last menstrual period and the day of delivery) and chronological age (the time elapsed since birth). The term “conceptional age (CA)” has been used based on the day of conception. The American Academy of Pediatrics now recommends using postmenstrual age, not the day of conception for determining GA. For example, a baby whose EEG is recorded at 4 weeks after birth with a GA of 30 weeks at the time of birth is 34 weeks CA. A baby born at 38 to 40 weeks GA is a full-term baby. A baby born at or before 38 weeks GA is considered to be premature. And, a baby born after 40 weeks GA is postmature. The survival of infants born before 34 or 35 weeks GA was not common 30 years ago, but today, it is not uncommon for a 24- to 26-week-GA baby to survive.

Other relevant clinical information includes blood gas, body temperature, serum electrolyte, and current medications. Also, technologists should consult nursing staff concerning the patient’s condition or any limitation in handing the baby.

The recording is preferably scheduled right after feeding time, since babies tend to sleep after feeding although an hourlong recording of most neonates should capture all stages of sleep and sleep-wake transitions. The technologist must observe the patient carefully throughout the recording and annotate the baby’s movement or behavioral changes. The notation may include eye opening and closing, head position, hiccups, sucking, breathing patterns, etc. The technologist should also note any unusual behaviors such as tonic posturing, clonic movement, eye deviation, skin color change, and other vital signs including SaO₂ saturation, blood pressure, and respiratory changes (Video 16-1). It is also important for the technologist to observe and note the baby’s state of consciousness. Routine use of video recording with EEG would be extremely helpful to correlate EEG findings with babies’ various behaviors.

Except for extremely premature infants (23 to 24 weeks GA), wakefulness is simply determined by eye opening and sleep is determined by eye closure. It may be possible to determine clinically if a baby is in active or quiet sleep, because of corresponding rapid eye movement (REM) or non-REM sleep, respectively, by observing the baby’s behavior. In active sleep, a baby may show a variety of facial, eyelid, arm, and leg twitches or body movements, sucking, or even crying. Under closed eyelids, REMs (rapid eye movements), predominantly in the horizontal direction, can be observed. Respiration becomes irregular, occasionally associated with apnea. The EEG during active sleep essentially consists of a low-voltage and continuous pattern, resembling quiet wakefulness (Fig. 16-1). In newborn infants, 50% of sleep time is active sleep, and sleep may start with active sleep directly from wakefulness. This pattern of active sleep onset may continue until about 4 months postterm, when quiet sleep becomes a prerequisite to entering active sleep. Also, the percentage of active sleep decreases rapidly to 20% to 25% of sleep time. In contrast to active sleep, quiet
sleep is characterized by few movements or twitches of face, head, limb, or trunk. Respirations are quiet and regular, without apnea. The EEG of quiet sleep consists of a variety of slow waves or bursts interrupted by a relatively low-voltage pattern representing trace discontinue (TD) (Fig. 16-2) or trace alternant (TA) (Fig. 16-3). It is important to capture quiet sleep because this may be the only state in which some EEG abnormalities become evident. The recording should include waking and all cycles of sleep including active and quiet sleep. Since active sleep occupies more than 50% of the sleep time in the neonate, a 1-hour recording will generally capture all states. After a satisfactory sleep record, the baby may be aroused while the recording continues. In order to capture all sleep stages and awake record, recording time for neonates should be at least 1 hour.

The first step of neonatal EEG analysis is to examine the degree of continuity of EEG activity. The second step is to examine the synchrony of EEG activity between homologous cortical areas. The third step is to evaluate the various EEG patterns characteristic for neonates and, lastly, to determine whether these features are appropriate for the stated CA.