RST cheat sheet

EEG electrode placement follows the 10-20 system; sleep staging relies on central (C3/C4), frontal (F3/F4), and occipital (O1/O2) derivations.

AASM adult sleep stages: W, N1, N2, N3, and R. Stage N2 is defined by K-complexes or sleep spindles; N3 requires slow waves 0.5-2 Hz with peak-to-peak amplitude >75 µV in >20% of an epoch.

REM requires low-amplitude mixed-frequency EEG, low chin EMG tone, and rapid eye movements; REM without atonia is scored when EMG tone remains elevated in REM.

An epoch is 30 seconds; staging is assigned by the majority rule for the stage occupying the greatest portion of the epoch.

Sleep onset latency = time from lights out to first epoch of any sleep stage; REM latency = sleep onset to first REM epoch.

EOG channels are placed to capture conjugate eye movements: left eye referenced to right mastoid and right eye to left mastoid (or equivalent bipolar montage).

EMG for sleep staging is typically chin (submental); limb EMG (anterior tibialis) is used for periodic limb movement scoring.

Oximetry sampling: SpO2 is averaged over 3 seconds for scoring; a desaturation event is a fall of >=3% (or >=4% per some criteria) from baseline.

PSG montage impedance should be <5 kOhm for reliable EEG/EOG/EMG signals; high impedance increases artifact and signal loss.

Apnea-Hypopnea Index (AHI) = (apneas + hypopneas) / total sleep time in hours; OSA severity: mild 5-15, moderate 15-30, severe >30 events/hour.

An apnea is a >=90% reduction in airflow for >=10 seconds; a hypopnea requires >=30% reduction with >=3% desaturation or an arousal (AASM recommended rule).

ODI (oxygen desaturation index) counts desaturation events per hour; it correlates with AHI but is not a substitute for AHI in diagnosis.

Excessive daytime sleepiness is quantified with the Epworth Sleepiness Scale (ESS, 0-24); >10 suggests abnormal sleepiness.

STOP-BANG screens OSA risk across 8 items; >=3 positive items indicates increased risk and warrants further evaluation.

CPAP adherence is commonly defined as >=4 hours per night on >=70% of nights; adherence is assessed over a 30-day window.

Insomnia disorder requires difficulty initiating/maintaining sleep or early awakening >=3 nights/week for >=3 months with daytime impairment.

Narcolepsy type 1 is characterized by CSF hypocretin-1 deficiency and cataplexy; mean sleep latency <=8 min with >=2 SOREMPs on MSLT supports diagnosis.

Restless legs syndrome is a clinical diagnosis: urge to move legs, worse at rest/evening, relieved by movement, and present >=3 times/week.