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• To understand the levels of evidence used in the development of
the new sleep scoring guidelines.
• To enumerate the differences between the Rechtschaffen and Kales
rules for sleep scoring and the new sleep scoring recommendations
of the American Academy of Sleep Medicine.
• To identify the recommended and alternative methods of electrode
and sensor placements.
• To describe the different electroencephalographic,
electrooculographic, and electromyographic features of the various
• To describe the new scoring rules for arousals, respiratory events,
and movement events.
• It has been 4 decades since Allen Rechtschaffen
and Anthony Kales1 standardized the method of
scoring polysomnographic recordings.
• Since then, major innovations in technology have
transformed the science and clinical practice of
• Documentation using paper and ink has been
replaced by the monitor screen and disc storage,
and analog systems of data collection and
retrieval have undergone digitization.
• Many researchers and clinicians in the field
have proposed a reexploration of the
conventional sleep scoring rules in order to
integrate the expanding knowledge of basic
neurobiology and the advances in
• An ideal sleep scoring system should have, at
least, several attributes.
• It must be physiologically relevant and based on true differences in
neurophysiology among the various sleep stages, rather than
merely a convenient visual recognition of waveforms.
• It must take into account the subtle changes in sleep architecture
associated with most sleep disorders (eg, insomnia), rather than
just sleep-related breathing disorders.
• The new rules should use the full potential of computerization of
data, including automation of sleep scoring, recognition of
disorders that occur during sleep, and integration with other
procedures, such as positive airway pressure titration.
• It also must allow taxonomic consistency and have minimal negative
impact on current research and epidemiologic conclusions.2
Overview of the Sleep Scoring
• This article describes and summarizes the
recommendations of the American Academy
of Sleep Medicine (AASM) regarding the
scoring of sleep stages, arousals, respiratory
events, cardiac events, and movement events.
• The task force adapted an evidence-based process in
determining their recommendations, which are
classified as standard (based on level 1 evidence or
overwhelming level 2 evidence), guideline (based on
level 2 evidence or a consensus of level 3 evidence),
consensus (less evidence than guideline, for which
agreement was reached in a standardized consensus
process based on available information) and
adjudication (recommendation from the steering
committee based on all available information, with
insufficient evidence and no consensus agreement)
Electrode and Sensor Placements
• Changes from the conventional Rechtschaffen
and Kales method of monitoring adult sleep
include the addition of frontal EEG leads,
placement of the electrooculographic (EOG)
electrodes closer to the outer canthus, the
addition of more chin electromyographic
(EMG) electrodes, the use of thermistors for
the detection of apneas, and the use of nasal
air pressure for identifying hypopneas.
• The recommended electrode placements for EEG are
F4M1, C4M1, and O2M1, with backup electrodes placed to
enable monitoring of F3M2, C3M2, and O1M2.
• The scoring guideline allows alternative placements,
including FzCz, CzOz, and C4M1, with backup electrodes
consisting of FpzC3, C3O1, and C3M2.
• Electrode placements are based on the International 10-20
system (F: frontal, C: central, O: occipital, M: mastoid; odd
numbers: left, even numbers: right, and z: midline).
• The addition of frontal leads was based on level 4 evidence
and determined by consensus agreement by the visual task
• E1M2 and E2M1 placements for EOG leads are
recommended, with E1 placed 1 cm below the left outer
canthus and E2 placed 1 cm above the right outer canthus.
• Alternative EOG placements include E1Fpz and E2Fpz, with
E1 situated 1 cm below and 1 cm lateral to the left outer
canthus and E2 placed 1 cm below and 1 cm lateral to the
right outer canthus.
• Electrode distances may be reduced to 0.5 cm for children.
• Placement of the EOG leads closer to the outer canthus was
arrived at by consensus based on level 4 evidence.
The following three chin EMG electrodes are recommended:
(a) midline at 1 cm above the inferior edge of the mandible,
(b) 2 cm to the right of midline and 2 cm below the inferior
edge of the mandible, and (c) 2 cm to the left of midline and
2 cm below the inferior edge of the mandible.
• The derivation consists of either of the inferior electrodes
(below the mandible) referred to the electrode placed above
the mandible, with the other inferior electrode being used as
a backup if the initial electrodes fail.
• Electrode distances may be reduced to 1 cm for children. No
evidence was provided for the additional chin EMG, and the
recommendation was based on consensus and adjudication
• A modified lead II, with electrodes placed
below the right clavicle and at the left 6th or
7th intercostal space, is recommended for ECG
Airflow (Apnea and Hypopneas)
• An oronasal thermal sensor is the recommended
method for identifying apneas.
• The nasal air pressure transducer is considered an
acceptable alternative method for detecting
• End tidal Pco2 or summed calibrated inductance
plethysmography can be used for children.
• The recommended sensor for hypopneas is the
nasal air pressure transducer.
• Alternative sensors for the detection of hypopneas
include inductance plethysmography or oronasal
• The use of thermistors as the preferred primary airflow
sensor for apneas and the use of nasal air pressure as
the preferred secondary airflow sensor for apneas
were both arrived at by consensus based on limited
• The use of nasal air pressure as the preferred airflow
sensor for identifying hypopneas was based on
consistent level 1-5 evidence and was considered a
standard practice recommendation.
• Respiratory Effort: Esophageal manometry or
inductance plethysmography (calibrated or
uncalibrated) are recommended for monitoring
respiratory effort, with the diaphragmatic or intercostal
EMG offered as an alternative sensor.
• Blood Oxygen and Ventilation: Pulse oximetry, with a
minimum acceptable signal averaging time of 3 s, is
recommended to measure blood oxygen levels.
• Transcutaneous or end-tidal Pco2 monitoring can be
used to detect the presence of alveolar hypoventilation
Scoring Rules for Sleep Stages
• Sleep stages are scored in 30-s epochs, with each epoch
being assigned a sleep stage comprising the greatest
percentage of the epoch.
• There are five wake-sleep stages: stage wake (W), stage
NREM 1 sleep (N1), stage NREM 2 sleep (N2), stage NREM 3
sleep (N3), and stage REM sleep (R).
• Stage N3 incorporates and replaces the Rechtschaffen and
Kales stages NREM 3 and NREM 4 sleep.
• Changes from the Rechtschaffen and Kales rules for scoring
sleep stages also include new recommendations for scoring
stage N2 and stage R, as well as the introduction of a new
pediatric stage NREM.
• An epoch is considered stage W if >50% of the
epoch has alpha EEG waves over the occipital
region during eye closure.
• Alpha waves have a frequency of 8 to 13 Hz.
• If alpha waves are absent, the presence of
conjugate vertical eye blinks; reading eye
movements; or voluntary, rapid open-eye
movements also defines stage W.
• For children at least 2 months postterm, alpha
activity is replaced by the dominant posterior
• In stage N1, alpha EEG waves (or dominant posterior EEG
rhythm in children) are replaced by low-amplitude, mixed-
frequency (4 to 7 Hz) waves that occupy >50% of the
• If alpha waves are not readily apparent, the presence of 4
to 7 Hz waves with slowing of background activity by at
least 1 Hz compared with stage W, vertex sharp waves, or
slow eye movements also can be used to document the
start of stage N1.
• In children, the development of rhythmic anterior theta
activity, hypnagogic hypersynchrony, or diffuse or occipital
predominant high-amplitude, 3 to 5 Hz, rhythmic activity
also suggests stage N1 sleep.
• Recommendations are provided defining the
start, continuation, and termination of stage
• The start of stage N2 is defined by the
presence of nonarousal K complexes or sleep
spindles during either the first half of the
epoch or the last half of the previous epoch, if
criteria for stage N3 are absent.
• (≥2 months postterm) are similar to the adult scoring
rulesStage N2 continues if low-amplitude, mixed-frequency
EEG rhythm is present in epochs that contain, or are
preceded by, K complexes or sleep spindles.
• Stage N2 ends with an arousal, a major body movement
not followed by stage N2, or when sleep transitions to stage
W, N1, N3, or R.
• Stage N2 scoring rules were arrived at by consensus based
on limited evidence.
• Stage N2 scoring rules for children.
• An epoch is scored as stage N3 if at least 20% of
the epoch is occupied by slow wave EEG activity
over the frontal regions.
• Slow waves have frequencies of 0.5 to 2 Hz and
amplitudes of greater than 75 µV.
• Consistent levels 1 and 2 or levels 3 and 4
evidence were used to formulate the stage N3
scoring rules, which were considered consensus
and standard practice recommendations.
• Stage N3 scoring rules for children (≥2 months
postterm) are similar to the adult scoring rules.
• Among children, an additional stage, NREM sleep
(N), can be used if K complexes, sleep spindles,
and slow waves are absent in all epochs of NREM
• The recommendation for a pediatric stage N was
arrived at by consensus based on either no
evidence or limited evidence.
• An epoch is considered stage R if it contains low-
amplitude, mixed-frequency EEG activity and low
chin EMG tone that is the lowest level in the
study or at least no higher than the other sleep
stages, and either has rapid eye movements or is
preceded by stage R sleep.
• It ends by transitioning to stage W, N1, N2, or N3
sleep. Recommendations for stage R sleep scoring
are based on consensus with limited evidence.
• Stage R scoring rules for children (≥2 months
postterm) are similar to the adult scoring rules
Major Body Movements
• The presence of movement or muscle artifact
that obscures the EEG for >50% of the epoch
is considered a major body movement.
• An epoch with a major body movement is
scored the same stage as the epoch that
follows it, except if alpha rhythm is present, or
if it is preceded or followed by a stage W
epoch, in which case it is scored as stage W.
Other Scoring Rules
An arousal during NREM sleep consists of an
abrupt EEG frequency shift (eg, alpha, theta,
or frequencies >16 Hz, but not spindles)
lasting at least 3 s and preceded by at least 10
s of stable sleep. A REM arousal is
characterized by similar EEG changes but
should be accompanied by an increase in chin
EMG that is at least 1 s in duration
• Apnea in adults consists of a decrease in peak
thermal sensor amplitude by at least 90% from
baseline for a duration of at least 10 s.
• It can be scored as either an obstructive, central,
or mixed event based on the presence or absence
of inspiratory effort throughout the entire period
or part thereof.
• In patients aged 18 years or younger, an apnea is
generally characterized by a fall in signal
amplitude by at least 90% lasting at least two
• Among adults is characterized by a reduction in nasal
pressure by at least 30% of baseline for a duration of at
least 10 s accompanied by an oxygen desaturation
• The hypopnea rules were based on consensus or
• In patients aged 18 years or younger, a hypopnea is
defined by a reduction in nasal pressure amplitude of
at least 50% compared with baseline, associated with
an arousal, awakening, or oxygen desaturation of at
least 3%, that lasts for a duration of at least two missed
Respiratory effort-related arousals
• In adults are described as breaths associated
with increasing respiratory efforts or flattening
of the nasal pressure waveform that lasts for
at least 10 s and precedes an arousal.
• They do not otherwise meet criteria for either
apnea or hypopnea.
• In patients aged 16 years or younger, respiratory effort-
related arousals are characterized by either of the
• 1.a decrease in sensor signal <50% of baseline levels,
associated with flattening of the waveform, snoring,
increase in end-tidal or transcutaneous Pco2, or visible
increase in work of breathing lasting at least two
breath cycles when a nasal pressure sensor is used; or
2.a progressive increase in inspiratory effort
accompanied by snoring, increase in end-tidal or
transcutaneous Pco2, or a visible increase in work of
breathing lasting at least two breath cycles when an
esophageal pressure sensor is used.
• Among adults is characterized as an increase in
Paco2 of at least 10 mm Hg during sleep
compared with supine awake values.
• No evidence was provided for this definition of
hypoventilation among adults, and the
recommended definition was based on
• Hypoventilation in patients aged 18 years or
younger is defined by transcutaneous or end-tidal
CO2 level >50 mm Hg in more than 25% of total
Cheyne Stokes breathing
• In adults consists of at least three consecutive
cycles of crescendo-decrescendo change in
respiration amplitude lasting at least 10
consecutive minutes or having at least five central
apneas/hypopneas per hour of sleep.
• This definition was not based on any evidence
and was a consensus recommendation.
• Periodic breathing in patients aged 18 years or
younger is characterized by more than three
episodes of central apneas with a duration of >3
s, separated by ≤20 s of normal respiration.
• Definitions of several cardiac arrhythmias are
included in the new sleep scoring guidelines.
These include asystole (a cardiac pause >3 s);
bradycardia (heart rate <40 bpm); sinus
tachycardia (heart rate >90 bpm); atrial
fibrillation (irregularly irregular rhythm with
variable P wave morphology); narrow-complex
tachycardia (heart rate >100 bpm with at least
three consecutive beats having a QRS duration of
<20 ms); and wide-complex tachycardia (heart
rate of >100 bpm with at least three consecutive
beats having a QRS duration of ≥120 ms).
• The AASM manual provides definitions of various
movement events that occur during sleep,
including alternating leg muscle activation
(consensus recommendation), bruxism (standard
recommendation), excessive fragmentary
myoclonus (consensus recommendation),
hypnagogic foot tremor (guideline
recommendation), periodic limb movements in
sleep, REM sleep behavior disorder, and rhythmic
A Final Word
• Science rests upon a standardized
classification system. This is true of sleep
medicine, as it is for widely diverse disciplines,
such as botany, astronomy, and geophysics.
• The new sleep scoring rules developed by the
AASM are not merely the result of the rapidly
expanding knowledge in the discipline of sleep
medicine; they will hopefully be the basis for
future advances in the field, as well.