How has the AASM manual for sleep stage scoring evolved?

Updated: Aug 19, 2019
  • Author: Andres A Gonzalez, MD, MMM, FACNS; Chief Editor: Selim R Benbadis, MD  more...
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This article is based on the updated 2016 American Academy of Sleep Medicine Manual for the Scoring of Sleep and Associated Events. [1] This manual represents the evolution and development of the 2007 AASM manual which was itself a restructuring, consolidation, and standardization of the original Rechtshaffen and Kales sleep scoring manual of 1968, commonly known as the "R and K" rules. [2]

Prior to the R and K rules, electroencephalographic (EEG) recording revealed distinct brain rhythms uniquely seen during sleep but were yet to be universally defined and categorized. Loomis and colleagues [3] noted fragmentation and fallout of alpha rhythm with sleep onset, the appearances of sleep spindles, K complexes and high amplitude slow waves. Sleep was divided into five stages (A-E), with later stages possessing more slow-frequency and high-amplitude waves [3] . The discovery of rapid eye movement (REM) sleep by Kleitman and Dement in 1957 [4] led to a classification of sleep stages that included REM sleep.

In 1968, Rechtschaffen and Kales convened a panel of experts to agree on a standardized manual for the scoring of sleep stages, which were then divided into wakefulness, stage 1-4 (non-REM), and REM. At least one EEG lead was recommended (C3 or C4 referenced to the opposite ear or mastoid) as well as two electrooculogram (EOG) leads and a submental electromyography (EMG) lead. The R and K rules recommended dividing the polysomnographic record of sleep into thirty second epochs, commencing at the start of the study. Historically, the 30-second interval was used because at a paper speed of 10 mm/s, ideal for viewing alpha and spindles, one page equates to thirty seconds. Each epoch was assigned a stage and if two or more stages coexist during a single epoch the stage comprising the majority of the thirty seconds was scored.

In 2004, the American Academy of Sleep Medicine (AASM) commissioned a steering committee to assemble a new sleep scoring manual that would address sleep staging as well as the scoring of arousals, respiratory, cardiac, and movement events. Eight separate task forces were assembled to address the various issues. The establishment of rules was guided by the following principles: the rules should be compatible with published evidence, they should be based on biologic principles, they should be applicable to both normal and abnormal sleep, and they should be easy to use by clinicians, technologists, and scientists.

In 2007, after three years of study, the AASM released their update which introduced key changes to the R and K system. The main revisions to sleep scoring from that manual included placement of a frontal EEG derivation in addition to the commonly used central and occipital leads. Previously, the R and K system required that the central lead always be used if only one derivation was possible, however, the AASM’s approach called for the utilization of frontal, central and occipital leads in all studies. Another major change was a reclassification of sleep stages to stage W (wake), stages N1-N3 (non-REM), and stage R (REM) from the previously described R and K stages of Wakefulness, 1-4, and REM. [5] The change in abbreviations is to avoid confusion between the two classification systems, where Stage 3 and 4 in the old R and K rules were combined to form stage N3 in the new rules since no physiologic or clinical basis has been found for a difference between Stages 3 and 4.

In the years following the transition from R and K to the adoption of the AASM scoring system of 2007 there have been some notable changes to polysomnographic data analysis with potential clinical effects. Outlined in a review from 2012, these include, but may not be limited to, large variances in adult apnea-hypopnea indexes when scored using the recommended versus alternative rules, decreases in N2 sleep with increases in N1 sleep and sleep transitions due to a rule governing transition from N2 to N1 sleep, increased N3 sleep in adults with the addition of frontal EEG lead tracings and improved slow wave detection, and improved interscorer reliability [6] . This article focuses on sleep stage scoring criteria from the 2015 AASM Manual [1] .

In April 2016, minor clarifications were made to the sleep scoring manual. The two changes that pertain to sleep staging are: 1) how to score epochs when multiple stages are present and 2) how to better capture arousals.


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