It is important to detect excessive sleepiness — defined as sleepiness that occurs in a situation when an individual would usually be expected to be awake and alert — because it is associated with morbidity and increased mortality, and can be treated in many cases . However, self-reported sleepiness is generally subjective and imprecise, which has led to the development of tests to quantify an individual's sleepiness [2-5].
The multiple sleep latency test (MSLT) and the maintenance of wakefulness test (MWT) use objective measures to quantify sleepiness. In contrast, the Epworth sleepiness scale (ESS) and Stanford sleepiness scale (SSS) subjectively quantify sleepiness. Other modalities used to assess sleepiness include the OSLER test and pupillometry.
Here, the approach to quantifying sleepiness is described and each of the tests used to quantify sleepiness is discussed. A general approach to the epidemiology, etiology, clinical features and diagnosis of excessive daytime sleepiness is discussed separately. (See "Approach to the patient with excessive daytime sleepiness".)
The following definitions are important for understanding the discussion that follows:
- Epoch — An epoch is a standard 30 second duration of a polysomnogram (PSG) to which a sleep stage can be assigned. In special situations, an epoch can be longer or shorter.
- Sleep onset — Sleep onset is the beginning of the first epoch with greater than 15 seconds of cumulative sleep of any stage.
- Sleep latency — Sleep latency is the duration from lights out to the onset of sleep.
- Mean sleep latency — The mean sleep latency is the average of the sleep latencies determined during a test.