Amplitude-integrated electro-encephalography: the child neurologist's perspective

Abstract

Neurologists increasingly recognize that critically ill patients are at high risk for seizures, particularly nonconvulsive seizures, and that neuromonitoring is a useful tool for diagnosing seizures and assessing brain function in these patients. Amplitude-integrated electroencephalography (EEG) is a simplified bedside neurophysiology tool that has become widely used in neonates over the past decade. Despite widespread interest by both neurologists and neonatologists in continuous brain monitoring, amplitude-integrated EEG has been largely ignored by neurologists, forcing neonatologists to "go it alone" when interpreting data from this bedside tool. Although amplitude-integrated EEG cannot replace conventional EEG for background monitoring and detection of seizures, it remains a useful instrument that complements conventional EEG, is being widely adopted by neonatologists, and should be supported by neonatal neurologists.

Keywords: electroencephalogram; epilepsy; hypoxic-ischemic encephalopathy; neonatal seizures; neurocritical; neurointensive care; seizure; status epilepticus.

Figure 1

Two channel (four-electrode) aEEG display. The upper two panels display single-channel EEG recorded from the left (top) and right (second from top) centro-parietal leads. The y-axis shows amplitude on a logarithmic scale; the y-axis shows time in seconds. The bottom two panels show the corresponding aEEG for each side. Note the rectification of voltages (with all values >0) and the time compression on the x-axis (this screen shows 3.5 hours of aEEG). The vertical bar indicates the segment of EEG displayed across the aEEG panels. (A) Normal or Continuous Normal Voltage (CNV): upper margin >10 μV and a lower margin >5 μV. (B) Moderately abnormal or Discontinuous Normal Voltage (DNV): upper margin >10 μV, lower margin <5 μV. The tracing is discontinuous and there is no sleep-wake cycling. (C) Burst Suppression (BS) is a pattern of mixed inactivity with bursts of higher amplitude. (D) Suppressed activity or Flat Tracing (FT) is defined by a low voltage/inactive aEEG with amplitude <5 μV; may be called called Continuous Low Voltage (CLV) when the background is around 5 μV.^,

Figure 2

The figure shows: aEEG voltage band (single channel C3–C4, panel A), and 3 segments of raw EEG corresponding to the vertical bar markers on aEEG (panels C, D, and E). At first glance, the aEEG voltage appears at or above 10 μV throughout (panel A). Review of raw EEG (panels C, D, and E), however, shows the overall aEEG background amplitude is elevated by artifact and seizure. Panel B shows the raw EEG with a seizure and concomitant electrocardiogram (EKG) artifact. Panel C shows EKG artifact during what might be an episode of post-ictal suppression. Panel D reveals a very suppressed background, apart from the EKG artifact, which is up-shifting the aEEG’s narrow voltage band by about 10 μV.

Figure 3

The top panel shows five hours of aEEG from a term neonate with encephalopathy. Note that in the first hour, the lower margin of the activity band is consistently above 5 μV, and thus might be misinterpreted as normal. However, review of the accompanying EEG below shows clear continuous seizures, which have elevated the overall amplitude on aEEG. The latter half of the aEEG shows the true background voltage after resolution of seizures; this aEEG is consistent with severe encephalopathy.

Figure 4

The top 3 panels display left, right, and crosscerebral aEEG, respectively. The bottom panel shows corresponding EEG signal at the time indicated by the arrow. Seizures are visible on aEEG as abrupt increases in amplitude, repeated throughout the first half of the aEEG. Seizures are confirmed by review of the corresponding EEG.

Figure 5

Brief seizures can be difficult to detect on aEEG, but they may be revealed upon review of the raw EEG. The arrow points to the aEEG at the time of the seizure displayed above, in the raw EEG channels.

Figure 6

In this example, a single machine is used to acquire the same data, which are displayed in differently for different users, optimizing the advantages of both aEEG and EEG. The bedside team sees the display at left, showing overall trends and allowing quick review of suspicious segments of EEG. The neurophysiologist can confirm these abnormalities through review of conventional, neonatal montage EEG.