Normal Sleep Architecture in Infants and Children

For children above 2 months of age – the sleep stages are very similar to the adult classification.

• Stage W (Awake)
• Stage N1 (NREM 1)
• Stage N2 (NREM 2)
• Stage N3 (NREM 3)
• Stage N (NREM)
• Stage R (REM)

For infants 0 – 2 months post term age, the sleep staging is different and is scored as-

• Stage W (Wakefulness)
• Stage N (NREM)
• Stage R (REM)
• Stage T (Transitional)

LVI – Low voltage irregular, M – Mixed, TA – trace alternant, HVS – High voltage slow

It has been proposed for a long time that infant sleep staging needs to be different from the adults. Based on EEG tracings, it was proposed to be divided into 2 main stages in sleep – Active sleep (corroborating to REM) and Quiet sleep (corroborating to NREM). Later on a 3rd stage called – Indeterminate stage was added, when the epochs were neither Active nor Quiet stage. The terminologies have later been changed to Stage W, N, R & T as stated above.

The other main difference is that in older children and adults, the sleep staging is purely done on basis of EEG. Where as in infants it is possible to score the sleep stage based on other recordings from polygraphy too, as tabulated below.

Sleep cycle, which is defined as an active sleep and quiet sleep along with the indeterminate sleep periods are shorter in infants. In fact, it ranges from 50 minutes at 36 weeks gestation to about 60 minutes at term. Lengthens to adult cycle between 2 – 5 years of age.

• Infants 4 months to 12 months should sleep 12 to 16 hours per 24 hours (including naps) on a regular basis.
• Children 1 to 2 years of age should sleep 11 to 14 hours per 24 hours (including naps) on a regular basis.
• Children 3 to 5 years of age should sleep 10 to 13 hours per 24 hours (including naps) on a regular basis.
• Children 6 to 12 years of age should sleep 9 to 12 hours per 24 hours on a regular basis.
• Teenagers 13 to 18 years of age should sleep 8 to 10 hours per 24 hours.
• The longest sustained sleep period increases from 3.5 hours at 3 months of age to 6 hours at 6 months.

Circadian rhythm of core body temperature is noticed from the first months of life, the amplitude of these rhythms increases by 3 months of age.

Early sleep spindles can be seen as early as 1.5 months, though they are better characterised and classical by 2 – 4 months of age.

Unlike adults, most the first sleep stage of most infants is R or REM sleep. This continues to be the pattern till 2-3 months post term. Later, NREM becomes the first stage of sleep as in adults.

Though sleep spindles and K – complexes and slow waves start appearing earlier, NREM can be scored as N1, N2 or N3 in most infants by 4-6 months of age.

Circadian rhythms of Heart rate, body movements, temperature, melatonin and cortisol are seen in the first months of life, but are better characterised by 3 months of age.

K-Complexes appear 3-6 months post term, Slow waves appear 2-5 months post term and Vertex waves appear 4-6 months post term.

By 6 – 8 months, infants can sleep through out the night without waking up for feeds.

At birth, infants sleep 50% of their sleep in REM, which drops to around 30% by 1 year of age and to adult levels of 20% by 3-5 years of age.

Common sleep disorders in this age group include – Behavioural insomnia of childhood – Excessive night waking, sleep associations (like rocking to sleep, feeding to sleep etc), Rhythmic body movements.

Sleep Disorders in different age groups-
3-5yrs- Behavioural insomnia of childhood – bed time refusal, Night terrors, OSA, Night mares and nighttime fears, parasomnias – sleep walking, sleep terrors
6-12yrs- Inadequate sleep due to social pressures, Sleep walking, OSA, Bruxism, Inadequate sleep hygiene
12-18yrs- Delayed sleep phase syndrome, Insufficient sleep, Insomnia, OSAS, Restless leg syndrome, Narcolepsy.