Table 1.
Description of Proposed Sleep Stages in Critically Ill Patients
| Sleep Stage (Current-Standard) | EE G Waveform Description |
| Wake | Alpha activity (8–13 Hz); relatively low voltage, mixed frequency EEG |
| N1 (NREM 1) | Relatively low voltage, mixed frequency EEG with >50% theta activity (4–7 Hz) |
| N2 (NREM 2) | Sleep spindles (12–14 Hz [>0.5 s]) and K-complexes (negative sharp wave followed immediately by slower positive component [>0.5 s]); on a background of relatively low voltage, mixed frequency EEG activity |
| N3 (NREM 3, slow wave sleep) | Delta activity, >20% high amplitude (>75 µV), slow frequency (0.5–2 Hz) |
| REM | Relatively low voltage, mixed frequency with intermittent REMs |
| Additional Sleep Stages Proposed for Atypical Sleep | |
| Sleep Stage (Proposed-Atypical)a | EE G Waveform Description |
| Pathologic wakefulness | Any EEG frequency other than alpha or beta with behavioral characteristics of wakefulness |
| At1 (Atypical 1) | Alpha and/or theta present on >10% of epoch, without sleep spindles or K-complexes in the preceding 3 min; may have polymorphic delta, FIRDA, or triphasic activity |
| At2 | Polymorphic delta, FIRDA, or triphasic activity with alpha or beta activity superimposed on delta waves, without sleep spindles or K-complexes in the preceding 3 min |
| At3 | Polymorphic delta, FIRDA, or triphasic activity without alpha or beta activity superimposed on delta waves |
| At4 | Burst-suppression pattern with EEG amplitude <5 µV for >0.5 s |
| At5 | Suppressed pattern with EEG amplitude <20 µV |
| At6 | Isoelectric activity (amplitude <5 µV) throughout epoch |
EEG = electroencephalography, NREM = non-rapid eye movement, REM = rapid eye movement, A = atypical, FIRDA = frontal intermittent rhythmic delta.
a
EEG examples for each of the proposed-atypical stages are shown in Figure 1.