Scoring, Interpretation, and Report Generation
Staging rules
Scoring uses 30-second epochs, assigned by the majority of the epoch. Wake: alpha rhythm over the occipital region for more than half the epoch (with eyes closed). N1: alpha replaced by low-amplitude mixed-frequency activity, slow eye movements, vertex sharp waves. N2: a K-complex or sleep spindle in the epoch or the preceding epoch, without an intervening arousal. N3: ≥20% of the epoch occupied by slow waves (0.5–2 Hz, >75 µV). R: low-amplitude mixed-frequency EEG, rapid eye movements, and the lowest chin EMG of the study.
Events
An arousal is an abrupt shift in EEG frequency lasting at least 3 seconds, preceded by at least 10 seconds of stable sleep; in REM it also requires a concurrent chin EMG increase. An apnea is a ≥90% reduction in airflow for ≥10 seconds; a hypopnea is a ≥30% reduction for ≥10 seconds with a ≥3% desaturation or an arousal. AHI is events per hour of sleep; RDI adds respiratory effort–related arousals. Periodic limb movements require at least four consecutive movements of 0.5–10 seconds with intervals of 5–90 seconds. Pediatric hypopnea criteria and obstructive apnea definitions differ from adult rules - read the age of the patient first.
Traps
Do not score by event count when the rule is epoch-based, and vice versa. Distinguish central from obstructive by effort, not by airflow. Remember desaturations lag the event by roughly 20–30 seconds.
Rule of thumb
When a desaturation appears, look backward about half a minute to find the respiratory event that caused it.