Sleep Laboratory Tests



Fig. 5.1
Matching sleep–wake disturbance to sleep laboratory tests





Nocturnal Polysomnography



Technical Aspects


The test consists of the recording of multiple physiological parameters during sleep. Most often this includes two to three channels of electroencephalogram (EEG), eye movements, chin and leg electromyogram (EMG), oronasal airflow, nasal pressure, thoracic and abdominal respiratory effort, oxygen saturation, and end-tidal carbon dioxide. The scalp EEG montage generally consists of C4-M1, F4-M1, plus O2-M1. The International 10–20 system is utilized for appropriate placement of EEG electrodes over the scalp [5]. Backup electrodes are placed at similar locations over the opposite scalp sites. Electrodes are fixed using collodion or paste while ensuring that the electrode impedance is kept low, i.e., below 5 kΩ. This helps to minimize picking up of extraneous artifact by the electrodes. The centrally placed EEG electrodes help to sample vertex sharp transients and sleep spindles, while occipital leads help to distinguish the waxing and waning amplitude alpha rhythm of wakefulness from the alpha to theta transition that is typical of stage N1 sleep as well as the predominant delta rhythm of stage N3, which is usually <4 Hz and >75 uv amplitude. In case of suspected nocturnal seizures, placement of a minimum 16-channel EEG montage is recommend. The usual sensitivity for EEG recording is 7 uv/mm, though it may need to be decreased to 10–15 uv/mm if the amplitude of the activity is too high, as happens in preschool-age children. Eye movements are generally recorded using a left outer canthus–right outer canthus montage, with the electrodes being placed in a slightly oblique plane in order to capture both horizontal and vertical eye movements. The transition from wakefulness into N1 sleep is associated with the onset of slow rolling eye movements, while transition to REM sleep is associated with rapid eye movements. Monitoring of end-tidal CO2 is essential in all patients to capture hypoventilation. If the EtCO2 sensor (it yields breath by breath values) is not tolerated by infants and toddlers due to anxiety or increased perioral sensitivity, a transcutaneous CO2 sensor can be utilized (this yields a trended value). For sampling the chin EMG, 2–3 electrodes need to be affixed under the chin. The absolute amplitude of the EMG is not relevant, but the relative changes in amplitude help distinguish wakefulness, NREM sleep, and REM sleep from each other.

Data are recorded and stored in a computerized polysomnogram system which is composed of preamplifiers for both alternative current (AC) and direct current (DC) input. The AC channels are useful for recording EEG, EMG, and eye movements, whereas the DC channels help record slow biopotentials like respiratory effort. Sleep is scored in 30 s epochs by the attending technologist, with subsequent verification of the scored record by a certified polysomnographer. Nap sleep studies are not recommended as the quantity and type of sleep sampled are variable. Only technician-attended, all night sleep studies are recommended. The technical guidelines for scoring sleep and sleep-related events have been published by the American Academy of Sleep Medicine.

For infants of age 2 months or less, sleep can be scored simply as active or quiet sleep, i.e., REM and NREM sleep. A low-voltage, irregular pattern is associated with active sleep while a high-voltage, slow pattern is characteristic of quiet sleep. After age 2 months, the standard criteria that are utilized in children and adults can be applied, with breakdown of NREM sleep into N1, N2, and N3 categories. For details about sleep scoring, the reader is again referred to the scoring manual of the American Academy of Sleep Medicine [1]. Parameters scored in polysomnography include start time, stop time, total time in bed, total sleep time, sleep efficiency, percentage of time spent in the various sleep stages, arousals per hour of sleep, percentage of arousals related to respiratory events, total number of apneas and hypopneas with attention to occurrence in REM or NREM sleep and relationship to body position, oxygen saturation nadir and mean, EtCO2 nadir, high and mean, percent of time with EtCO2 greater than 50 mm, frequency of periodic limb movements, and comments about any unusual events observed in the simultaneous video recording. A flattened contour on the nasal pressure tracing may be indicative of the upper airway resistance type of obstructive sleep apnea. The polysomnogram report should provide data in a tabular form, coupled with narrative about the overall impression and recommendations of the polysomnographer.


Indications


The definitions of levels of evidence utilized by the AASM and how emphatic the recommendation are for PSG in specific sleep disorders are shown in Table 5.1 [refs 24]. The investigation of sleep-disordered breathing is a major indication for PSG (Standard). This includes habitual snoring, suspected obstructive sleep apnea, obstructive hypoventilation, central sleep apnea, and congenital central hypoventilation syndrome. Monitoring of end-tidal carbon dioxide (EtCO2) or, if this is not available, transcutaneous carbon dioxide is mandatory for assessing hypoventilation – this is a major component of sleep-disordered breathing in Down syndrome, Prader–Willi syndrome, obesity, neuromuscular disorders, and kyphoscoliosis. Reference values for respiratory parameters differ from those of adults. For instance, the duration of obstructive apneas in children is generally in the 5–10 s range (two-breath duration), whereas in adults, scored obstructive apnea events are invariably 10 s or longer in duration. The investigation of excessive daytime sleepiness, including suspected narcolepsy, requires a PSG followed the next day by the multiple sleep latency test (MSLT). This recommendation is also at Standard level (Table 5.1). A key tenet in narcolepsy is that there is excessive daytime sleepiness despite adequate sleep duration at night. PSG is also indicated in nonverbal children with suspected restless legs syndrome/periodic limb movement disorder in order to document presence of periodic limb movements in sleep. In this regard, preschool-age children are often candidates for PSG. Reference values for the periodic limb movement index in children have been extrapolated from adults at 5 or less. With regard to parasomnias, PSG is not indicated routinely as clinical history may be sufficient to make a diagnosis. If there are recurrent parasomnia-like events or if one is unable to exclude the diagnosis of nocturnal seizures, however, PSG is indicated. The investigation of nocturnal seizures requires the utilization of a 16–18 channel EEG montage. REM sleep behavior disorder may accompany daytime sleepiness in children with narcolepsy–cataplexy; hence, when PSG is being conducted for diagnosing narcolepsy, it is important to carefully examine segments of REM sleep for the presence of the electrophysiological marker of RBD, i.e., persistence of muscle tone during REM sleep, which is also called REM sleep without atonia.


Table 5.1
AASM level of recommendation for polysomnography and sleep disorder
























Level

Definition

Disorder

Standard

This is a generally accepted patient care strategy that reflects a high degree of clinical certainty and generally implies the use of level 1 evidence or overwhelming level 2 evidence

Periodic limb movement disorder

Narcolepsy

Diagnosis of obstructive sleep apnea, to evaluate for residual obstructive sleep apnea after adeno-tonsillectomy; follow-up of children on chronic PAP support, for PAP titration

Guideline

This is a patient care strategy that reflects a moderate degree of clinical certainty and implies the use of level 2 evidence or a consensus of level 3 evidence

NREM parasomnias, epilepsy, nocturnal enuresis, assessment of sleep-related hypoventilation, apparent life-threatening event

Option

This is a patient care strategy that reflects uncertain clinical use and implies either inconclusive or conflicting evidence or conflicting expert opinion

Restless legs syndrome, when supportive information is needed for diagnosis; hypersomnia from causes other than narcolepsy; follow-up of children needing oral appliance or rapid maxillary expansion; patients on mechanical ventilation for adjustment of their machine settings; tracheostomy patients being considered for decannulation, if there is suspicion of a sleep disorder in cystic fibrosis/asthma/kyphoscoliosis/pulmonary hypertension


Limitations


PSG is the gold standard procedure for the investigation of many childhood sleep disorders. It is however an expensive and labor-intensive tool. Patient and parent anxiety about the procedure may affect variables such as sleep latency, REM latency, and sleep efficiency. There might also be some degree of night to night variability in parameters like periodic limb movement index. Alternative strategies for diagnosing obstructive sleep apnea include home overnight oximetry. This procedure has limited sensitivity, however, and may be positive only in severe cases. Consequently, if oximetry is noninformative in a child with suspected OSA, one might still need to resort to PSG. The Pediatric Sleep Questionnaire (PSQ) and the Sleep Disturbance Scale for Children (SDSC) may be applied for screening for sleep-disordered breathing [6, 7], but PSG is unfortunately still necessary to confirm the diagnosis.


Multiple Sleep Latency Test (MSLT)


In combination with the nocturnal polysomnogram, the MSLT forms the gold standard in the assessment of daytime sleepiness in both children and adults. This applies especially to the diagnosis of narcolepsy and idiopathic hypersomnia. The strengths of the test lie in its intuitive design (sleepy individuals are likely to fall asleep more quickly in the daytime than those who are not sleepy), its reliability, and the availability of normative data across various ages [8].

The lower age limit at which one can apply the MSLT seems to be 5–6 years [9]. Application of the MSLT in children younger than this age is difficult because physiological daytime napping is common in preschool-age children. To the extent possible, the total sleep time on the preceding night’s PSG must be similar to the sleep duration at home. As sleep loss in the days prior to the MSLT may influence the test findings, the parents should be advised to keep a log of the patient’s sleep–wake schedule for 1–2 weeks prior to the MSLT. Alternatively, wrist actigraphy for 1–2 weeks prior to the PSG and MSLT can be utilized to gauge sleep time and sleep schedules at home. Medications that can influence sleep, such as stimulants/antidepressants/benzodiazepines/antihistamines, should be discontinued at least 2 weeks prior to the test. Long-acting selective serotonin reuptake inhibitors like fluoxetine that suppress REM sleep may need to be stopped for 4–6 weeks prior to the PSG and MSLT. The decision to stop antidepressants for the purpose of obtaining valid PSG and MSLT should be carefully thought out after weighing the risks and benefits. A discussion with the prescribing physician is also indicated in this regard. The patient’s general physical examination should include a Tanner staging of sexual development as normal values for the mean sleep latency in children vary according to individual stages (Table 5.2; [10]). The test consists of the provision of four or five daytime nap opportunities at two hourly intervals, e.g., 0900, 1100, 1300, 1500, and 1700 h, during which the EEG, chin EMG, and horizontal as well as vertical eye movements (using at least two channels) are monitored. The time constant for the electrooculogram should be long enough to allow for the recording of slow, rolling eye movements seen at the onset of N1 sleep (250 ms). Electrode impedances should be below 5 kΩ.


Table 5.2
Reference values for the MSLT







































Tanner stage

General corresponding age (years)

Mean sleep latency

Standard deviation

Stage 1

<10

18.8

1.8

Stage 2

10–12

18.3

2.1

Stage 3

11.5–13

16.5

2.8

Stage 4

13–14

15.5

3.3

Stage 5

>14

16.2

1.5

Only gold members can continue reading. Log In or Register to continue

Stay updated, free articles. Join our Telegram channel

Aug 15, 2017 | Posted by in NEUROLOGY | Comments Off on Sleep Laboratory Tests

Full access? Get Clinical Tree

Get Clinical Tree app for offline access