How is stage N2 scored in sleep stage scoring?

Updated: Aug 19, 2019
  • Author: Andres A Gonzalez, MD, MMM, FACNS; Chief Editor: Selim R Benbadis, MD  more...
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Answer

Answer

Stage N2 sleep is scored when either one or more K complexes is noted (and unassociated with an arousal) or one or more trains of sleep spindles appear.

Stage N2. Note K complexes unassociated with arous Stage N2. Note K complexes unassociated with arousal and trains of sleep spindles.

Stage N2 sleep should continue to be scored in subsequent epochs of mixed frequency, low-amplitude activity even if K complexes or sleep spindles are absent. Stage N2 sleep should no longer be scored when one of the following five morphological changes occur: (1) there is a transition to Stage W; (2) an arousal (see “special considerations” below; (3) a major body movement followed by slow eye movements and low-amplitude mixed EEG without nonarousal associated K complexes or sleep spindles; (4) transition to stage N3; (5) transition to stage R.

Stage N2 is the equivalent to the R and K stage II. It is characterized by the presence of sleep spindles and K complexes on a background of low-amplitude, mixed frequency EEG activity.

Sleep spindles are trains of higher frequency bursts that were named according to their shapes, which tend to have tapering ends. They are seen maximally over the central leads, have a frequency of 11-16 Hz, and last 0.5 seconds or longer. K complexes are well-delineated, negative, sharp waves followed by a positive deflection and tend to stand out from the background signal. Their duration is 0.5 seconds or longer and are more commonly encountered over the frontal derivations.

Stage N2. Note K complexes unassociated with arous Stage N2. Note K complexes unassociated with arousal and trains of sleep spindles.

K complexes can also be associated with arousals but are only counted as such when the arousal is concurrent with the K complex or commences within one second of the end of the K complex.


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