Quantitative Sleep Monitoring - Quantitative EEG Analysis Methods and Clinical Applications - page 271

ing is seen primarily in premature infants and mainly during active sleep [34].
Although controversial, some feel that the presence of periodic breathing for 5%

of TST or during quiet sleep in term infants is abnormal. Central apnea in infants is
thought to be abnormal if the event is >20 seconds in duration or associated with
arterial oxygen desaturation or significant bradycardia [34-37].
In children, a cessation of airflow of any duration (usually two or more respira-
tory cycles) is considered an apnea when the event is obstructive [34-37]. Of note,
the respiratory rate in children (20 to 30 per minute) is greater than that in adults
(12 to 15 per minute). In fact, 10 seconds in an adult is usually the time required for
two to three respiratory cycles. Obstructive apnea is very uncommon in normal
children. Therefore, an obstructive AHI

>

1 is considered abnormal. In children with
obstructive sleep apnea, the predominant event during NREM sleep is obstructive
hypoventilation rather than a discrete apnea or hypopnea. Obstructive hypoventila-
tion is characterized by a long period of upper-airway narrowing with a stable
reduction in airflow and an increase in the end-tidal PCO 2 . There is usually a mild
decrease in the arterial oxygen desaturation. The ribcage is not completely calcified
in infants and young children. Therefore, some paradoxical breathing is not neces-
sarily abnormal. However, worsening paradox during an event would still suggest a
partial airway obstruction. Nasal pressure monitoring is being used more fre-
quently in children and periods of hypoventilation are more easily detected (reduced
airflow with a flattened profile). Normative values have been published for the
end-tidal PCO 2 . One paper suggested that a peak end-tidal PCO 2 >

>

53 mm Hg or

end-tidal PCO 2 > 45 mm Hg for more than 60% of TST should be considered

abnormal [35].
Central apnea in infants was discussed above. The significance of central apnea
in older children is less certain. Most do not consider central apneas following sighs
(big breaths) to be abnormal. Some central apnea is probably normal in children,
especially during REM sleep. In one study, up to 30% of normal children had some
central apnea. Central apneas, when longer than 20 seconds, or those of any length
associated with SaO 2 below 90%, are often considered abnormal, although a few
such events have been noted in normal children [38]. Therefore, most would recom-
mend observation alone unless the events are frequent.

10.12 Leg Movement Monitoring

The EMG of the anterior tibial muscle (anterior lateral aspect of the calf) of both
legs is monitored to detect leg movements (LMs) [39]. Two electrodes are placed on
the belly of the upper portion of the muscle of each leg about 2 to 4 cm apart. An
electrode loop is taped in place to provide strain relief. Usually each leg is displayed
on a separate channel. However, if the number of recording channels is limited, one
can link an electrode on each leg and display both leg EMGs on a single tracing.
Recording from both legs is required to accurately assess the number of movements.
During biocalibration, the patient is asked to dorsiflex and plantarflex the great toe
of the right and then the left leg to determine the adequacy of the electrodes and
amplifier settings. The amplitude should be 1 cm (paper recording) or at least
one-half of the channel width on digital recording.