Chapter 78: Use of aEEG/NIRS

AMPLITUDE-INTEGRATED ELECTROENCEPHALOGRAPHY

What Is Amplitude-Integrated Electroencephalography?

Amplitude-integrated electroencephalography (aEEG) is a simplified, bedside EEG device used to continuously monitor brain function. Brain wave activity is recorded from scalp electrodes, and the raw EEG data are processed using a filter to attenuate frequencies less than 2 Hz and greater than 15 Hz, transform the amplitudes into a rectified and time-compressed signal, and display on a semilogarithmic scale in microvolts (μV). This results in patterns that are easily recognizable without formal training in EEG analysis. Interpretation of the aEEG recording includes assessment of the minimum amplitude, maximum amplitude, bandwidth, and the presence of sleep-wake cycles (SWCs) (Figure 78-1).

Indications for aEEG Monitoring

The following are indications for aEEG monitoring:

1. Confirmation of suspected clinical seizures, especially when formal EEG is not available

2. Assessment for subclinical seizures in high-risk infants

3. Continuous monitoring of therapeutic effects of antiepileptic medication

4. Prediction of outcomes in hypoxic ischemic encephalopathy (HIE)

5. Other potential, but not well-studied, uses for aEEG include metabolic encephalopathy, patients on extracorporeal membrane oxygenation (ECMO), assessment of neuromaturation in preterm infants, assessment of posthemorrhagic hydrocephalus, surgical anesthesia, and postoperative recovery

Placement of aEEG

1. Types of electrodes

   1. Hydrogel: disposable electrodes similar to regular electrocardiographic (ECG) electrodes; used in most commercial aEEG devices

   2. Cup-disk: reusable; requires EEG conductive paste

   3. Needle: minimal skin preparation required and achieves low impedances; invasive, with theoretical risk for infection

2. Recording montages: location of electrodes based on the 10–20 international classification system modified for neonates (Figure 78-2)

   1. Single channel: Traditionally, electrodes are positioned at P3 and P4, which is the area overlying the cortical watershed zone in infants with HIE; alternatively, if using the CoolCap^® System, electrodes may be modified to Fp1 and Fp2.

   2. Three channel: Electrodes positioned at C3, P3, C4, P4 create two biparietal channels (C3-P3, C4-P4) and a cross-cerebral channel (P3-P4).

   3. All devices require an additional ground electrode, usually placed on the back or forehead. Some devices may also require a reference electrode on the scalp (typically Cz).

   4. Other EEG recording systems may utilize additional channels.

3. Skin preparation: When cup-disk or hydrogel electrodes are used, skin should be cleaned and exfoliated prior to application.

4. Data quality: Impedance is continuously measured during the aEEG recording. Impedances greater than 10 kΩ indicate poor electrode contact, insufficient skin preparation, or electrical interference, and the electrodes should be checked.