How are sleep and wake states identified in the visual analysis of neonatal electroencephalogram (EEG)?

Updated: Nov 08, 2018
  • Author: Samuel Koszer, MD; Chief Editor: Selim R Benbadis, MD  more...
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Answer

Answer

The observation of the infant's movements, description of the infant's behavior by the technician, and analysis of the data in the noncerebral electrodes determine the neonate's state. Table 2 below describes types of activity expected for each state. Lateral eye movements, ventilatory rate, and ECG and EMG patterns do not become reliable indicators of state, however, until 34-36 weeks postconceptional age.

EEG is a useful test in providing reliable clues for assessing postconceptional age. Quantification of various sleep states from the newborn period to adulthood show that FT infants spend more time in rapid eye movement (REM) sleep than any other age group. [3] Furthermore, as a PT baby approaches FT, the amount of nonrapid eye movement (NREM) sleep increases, while REM sleep decreases. [4] Quiet sleep is analogous to NREM sleep, and active sleep is analogous to REM sleep in the adult. Quiet sleep is characterized by an absence of lateral eye movements and increased chin EMG activity with regular respirations and ECG. See the image below.

Quiet sleep and tracé alternant (TA). An infant of Quiet sleep and tracé alternant (TA). An infant of 39 weeks' postconceptional age with hydrocephalus and possible seizures. During quiet sleep, respirations are regular, EMG activity is low-voltage tonic with no phasic activity, and no spontaneous eye movements occur. TA is seen with medium- to high-voltage mixed frequencies alternating with periods of relative voltage attenuation.

Neonates often enter active sleep at onset of sleep. Low-to-moderate voltage, continuous EEG pattern with rapid eye movements; irregular respirations and cardiac rate; decreased chin EMG activity; and quick irregular movements of the fingers, hand, or face characterize active sleep. By term, 2 patterns of REM may be seen if the recording continues long enough. In the first REM cycle, the EEG shows fairly continuous mixed frequencies in the delta, theta, and alpha ranges with a paucity of faster activity, and the voltages range from 40-l00 µV. In the second REM cycle, which occurs after a period of NREM sleep, the background is more continuous, voltage is lower (20-50 µV), and frequencies are faster than in the first REM period. See the image below.

Active sleep. An otherwise healthy infant of 41 we Active sleep. An otherwise healthy infant of 41 weeks' postconceptional age with episodes of arm and leg extension without EEG correlates. This segment of normal, active sleep shows irregular respirations; frequent eye movements on EOG; and a mixed pattern of delta, theta, and alpha frequency activity.

Delta brushes are present in the premature infant beginning at 26 weeks' postconceptional age. Delta brushes are analogous to K complexes in the adult; however, they typically occur asynchronously in the neonate. Delta brushes consist of a mixture of medium- to high-voltage delta activity intermixed with low- to medium-voltage fast activity, commonly with 18- to 22-Hz maximum in the central region. Delta brushes are a prominent feature in active sleep by 29-33 weeks' postconceptional age, and, by 33-38 weeks' postconceptional age, they are expressed maximally in quiet sleep.

Prior to 28-30 weeks' postconceptional age, the record is discontinuous, with interbursts of low voltage or inactivity alternating with higher amplitude and mixed-frequency activity, a pattern termed tracé discontinu (TD). See the image below.

Tracé discontinu (TD). An infant of 24 weeks' gest Tracé discontinu (TD). An infant of 24 weeks' gestational age at age 4 weeks with an intraventricular hemorrhage and left shoulder twitching. Periods of alternating high-voltage mixed frequencies and periods of voltage suppression are normal findings before 28-30 weeks' postconceptional age.

Beginning at 28-30 weeks' postconceptional age, some sleep-state differentiation occurs, with active sleep having more continuous patterns than quiet sleep. However, sleep-state differentiation may be difficult until 32-34 weeks' postconceptional age. As the infant matures, the interburst durations decrease, and the amplitude and morphologies of the interburst activity change. Beginning at approximately 34-35 weeks' postconceptional age, other physiological features become increasingly helpful in determining sleep state.

Tracé alternant (TA) is defined as the discontinuous pattern of NREM sleep in which bursts of prevalent slow activity (1-4 Hz) alternate with random, faster transients at 50-200 µV. The bursts appear about every 4-5 seconds and last 2-4 seconds. The interburst consists of low-voltage, continuous, somewhat rhythmic activity with a dominant frequency in the theta range and voltages between 20-50 µV. TA usually emerges by 36-38 weeks' postconceptional age. See the image below.

Tracé alternant (TA). An infant of 42 weeks' postc Tracé alternant (TA). An infant of 42 weeks' postconceptional age delivered via cesarean birth, with Apgar scores of 4/4/4 and left arm and leg jerking movements. TA occurs with regular respirations, low-voltage tonic EMG, and minimal eye movements. Periods of relative voltage attenuation may occur periodically during quiet sleep.

By term, the infant often has a slow wave sleep pattern (SWS) of NREM state, which consists of prominent diffuse delta with some theta rhythms. Although some brief periods of SWS can occur as early as 36 weeks' postconceptional age, the amount of SWS gradually increases until 44-48 weeks' postconceptional age, when it almost completely replaces the TA pattern.

Table 1. State-related Polygraphic Changes in the Neonate (Open Table in a new window)

Physiological Measure

Awake/Sleep State

Awake

Active Sleep

Quiet Sleep

EMG (chin)

Phasic and tonic

Phasic

Tonic

Respiration

Irregular

Irregular

Regular

Eye movements

Random or pursuits

Rapid eye movements

Absent

Body movements

Facial, limbs, and body

Sucking and irregular limb movements

None


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