Polysomnography (PSG) is a useful tool for the diagnosis of sleep disorders in children. This multichannel study obtains information about sleep architecture, respiratory effort, movements during sleep, respiratory events, and gas exchange to facilitate the evaluation of children who have disrupted sleep or suspected SDB. Children should be studied in a sleep laboratory equipped for and staffed with personnel comfortable with and experienced in the performance of PSG in children. The scoring and interpretation of PSG differs in children and adults. The pediatric PSG should be interpreted by a pediatric professional knowledgeable in normal development and sleep disorders in children.
Polysomnography (PSG) is important in the evaluation of nocturnal events in children as well as adults. Events that can be evaluated include obstructive sleep apnea syndrome (OSAS), periodic leg movements (PLM), nocturnal seizures, parasomnias, and issues related to nocturnal gas exchange. This article discusses the use of PSG primarily in terms of respiratory events, leg movements, and gas exchange problems in children.
PSG has been recommended to evaluate several conditions in children, including
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Differentiation of benign from pathologic snoring
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Disrupted sleep
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Excessive daytime sleepiness
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Unexplained failure to thrive
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Cor pulmonale
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Polycythemia
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Laryngomalacia in children when worsened with sleep
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Underlying disorders predisposing children to nocturnal hypoxemia or hypoventilation, such as bronchopulmonary dysplasia, cystic fibrosis, neuromuscular disorders (muscular dystrophy, spinal muscular atrophy, cerebral palsy, or congenital muscle diseases)
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Suspected alveolar hypoventilation
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Confirmation of clinical diagnosis of airway obstruction suggested by symptoms including apnea, paradoxical respirations, or increased work of breathing
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Documentation of severity of obstructed breathing to guide therapeutic intervention and identification of those at increased risk of postoperative complications
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Titration of positive pressure for medical treatment of OSAS
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Follow-up evaluation of children who have persistent symptoms postintervention for OSAS
Sleep disordered breathing (SDB) is a common cause of morbidity in childhood, with a spectrum ranging from benign snoring to complete airway obstruction. Benign or primary snoring is reported in 3% to 12% of the pediatric population, with OSAS affecting 1% to 3% . Several authors have demonstrated that clinical history and physical examination are not accurate in the identification of children who have OSAS . PSG is useful in documenting the presence of obstructive sleep apnea (OSA) events as well as their severity. PSG has been recommended as the test of choice to evaluate SDB by consensus of a panel of experts . PSG has also shown to be useful in determining readiness for decannulation in children who have tracheostomy .
Performance of polysomnography in children
PSG should be performed by a laboratory experienced in and comfortable with caring for children . Technicians need to be experienced in dealing with children of various age levels and developmental status. Personnel should be certified in pediatric cardiopulmonary resuscitation. If a dedicated pediatric facility is not available, an area in the adult sleep laboratory should be designated for children. Children should be housed in an appropriate environment, with accommodations for a caregiver to sleep near the child. Caregiver availability to the child is important to minimize the child’s anxiety or fears about the study, as well as to provide any necessary care. The procedure should be explained to the child and the family by personnel skilled in the presentation of medical information. A crib should be available for small children. The person responsible for supervision of the pediatric sleep facility or functions should be a pediatrician with training and expertise in the area of sleep medicine. This person must assure that the PSG performance, scoring, and interpretation are appropriate for the age and condition of the child.
The study timing should be set to mimic the child’s bedtime as closely as possible. Overnight studies are preferred because negative nap studies have been shown not to exclude the possibility of OSAS during a night study . Studies should be performed without sedation in order to most accurately mimic the child’s normal sleep.
Components of polysomnography in children
Variables gathered during PSG in children are similar to those obtained in adults, with some additional information. Children may often demonstrate obstructive hypoventilation as a component of their OSAS, which may only be detected by increased carbon dioxide (CO 2 ) levels . Thus, PSG monitoring in children should include some method of determining CO 2 levels, such as end tidal CO 2 or transcutaneous CO 2 . The many channels of physiologic parameters and their purpose in the PSG are described in the following sections .
Sleep stages are determined using electroencephalogram (EEG), chin electromyogram (EMG), and electro-oculogram (EOG). EEG monitoring includes two central and two occipital leads with references to the opposite posterior auricular area. Additional EEG leads can be used to detect nocturnal events such as seizure activity. Three chin EMG leads are placed and used to detect skeletal muscle activity as required for the identification of rapid eye movement (REM) sleep. The chin EMG is also useful to detect swallowing and sucking during the study. Right and left EOG leads are used to detect eye movements essential to the identification of REM sleep.
Respiratory effort is detected using chest and abdominal belts. Different styles of monitoring include strain gauges, chest wall impedance, inductance plethysmography, intercostal EMG, and pneumatic transducers . These belts can assess qualitative respiratory effort, which is essential to distinguishing whether respiratory events are central or obstructive in origin. Air entry is assessed using a thermistor, nasal pressure, and a capnograph tracing. The thermistor detects airflow at the nose and mouth by detecting a temperature change in expired gas. Nasal pressure is an additional method of monitoring airflow by detecting pressure changes via a cannula placed in the nose. A recent study showed that the nasal pressure transducer is more sensitive in the detection of hypopnea, and suggested combining the use of both the thermistor and nasal pressure transducer for optimal detection of SDB in children . During positive pressure titrations, flow is detected using measurements from the positive pressure device.
Movements of extremities are monitored by EMG leads placed on the legs and sometimes on the arms. These movements are important in documenting PLM as well as movements that result from respiratory events. Position sensors can be used to document patient position. Digital video is also obtained. The video is useful in documenting patient position, movements, and unusual episodes such as parasomnias. Snoring is assessed by a snore microphone placed on the neck of the patient, by technician observation, and by audio recording.
Gas exchange is assessed using monitoring for both oxygen and CO 2 . Oxygenation is monitored by pulse oximetry, using a comfortable sensor that can be left on the child for the duration of the study. It is essential that the pulse oximeter have a short sampling time (2 to 3 seconds) to avoid missing brief desaturations associated with events in children. The reliability of the pulse oximeter tracing is improved with recording of the pulse amplitude signal, allowing identification of desaturation events that are caused by poor probe function . Ventilation is monitored in children by either end tidal (ET) CO 2 or transcutaneous CO 2 monitoring. The ET CO 2 method is more responsive to rapid changes, whereas the transcutaneous method is not reflective of transient CO 2 changes, and is most useful for a trend . ET CO 2 is monitored by a probe placed at the nose and mouth. ET CO 2 generates a flow tracing that can also be used to monitor airflow. The sensor for the transcutaneous device must be changed every several hours to maintain accuracy. In patients with persistent gas exchange abnormalities, access to arterial blood gas measurement is useful in corroborating noninvasive monitoring of gas exchange. This can be useful in a patient who has alveolar hypoventilation, to accurately assess the extent of CO 2 retention, or in a patient who has sickle cell disease with abnormal hemoglobin, in whom the pulse oximetry may not accurately reflect arterial oxygen level .
Components of polysomnography in children
Variables gathered during PSG in children are similar to those obtained in adults, with some additional information. Children may often demonstrate obstructive hypoventilation as a component of their OSAS, which may only be detected by increased carbon dioxide (CO 2 ) levels . Thus, PSG monitoring in children should include some method of determining CO 2 levels, such as end tidal CO 2 or transcutaneous CO 2 . The many channels of physiologic parameters and their purpose in the PSG are described in the following sections .
Sleep stages are determined using electroencephalogram (EEG), chin electromyogram (EMG), and electro-oculogram (EOG). EEG monitoring includes two central and two occipital leads with references to the opposite posterior auricular area. Additional EEG leads can be used to detect nocturnal events such as seizure activity. Three chin EMG leads are placed and used to detect skeletal muscle activity as required for the identification of rapid eye movement (REM) sleep. The chin EMG is also useful to detect swallowing and sucking during the study. Right and left EOG leads are used to detect eye movements essential to the identification of REM sleep.
Respiratory effort is detected using chest and abdominal belts. Different styles of monitoring include strain gauges, chest wall impedance, inductance plethysmography, intercostal EMG, and pneumatic transducers . These belts can assess qualitative respiratory effort, which is essential to distinguishing whether respiratory events are central or obstructive in origin. Air entry is assessed using a thermistor, nasal pressure, and a capnograph tracing. The thermistor detects airflow at the nose and mouth by detecting a temperature change in expired gas. Nasal pressure is an additional method of monitoring airflow by detecting pressure changes via a cannula placed in the nose. A recent study showed that the nasal pressure transducer is more sensitive in the detection of hypopnea, and suggested combining the use of both the thermistor and nasal pressure transducer for optimal detection of SDB in children . During positive pressure titrations, flow is detected using measurements from the positive pressure device.
Movements of extremities are monitored by EMG leads placed on the legs and sometimes on the arms. These movements are important in documenting PLM as well as movements that result from respiratory events. Position sensors can be used to document patient position. Digital video is also obtained. The video is useful in documenting patient position, movements, and unusual episodes such as parasomnias. Snoring is assessed by a snore microphone placed on the neck of the patient, by technician observation, and by audio recording.
Gas exchange is assessed using monitoring for both oxygen and CO 2 . Oxygenation is monitored by pulse oximetry, using a comfortable sensor that can be left on the child for the duration of the study. It is essential that the pulse oximeter have a short sampling time (2 to 3 seconds) to avoid missing brief desaturations associated with events in children. The reliability of the pulse oximeter tracing is improved with recording of the pulse amplitude signal, allowing identification of desaturation events that are caused by poor probe function . Ventilation is monitored in children by either end tidal (ET) CO 2 or transcutaneous CO 2 monitoring. The ET CO 2 method is more responsive to rapid changes, whereas the transcutaneous method is not reflective of transient CO 2 changes, and is most useful for a trend . ET CO 2 is monitored by a probe placed at the nose and mouth. ET CO 2 generates a flow tracing that can also be used to monitor airflow. The sensor for the transcutaneous device must be changed every several hours to maintain accuracy. In patients with persistent gas exchange abnormalities, access to arterial blood gas measurement is useful in corroborating noninvasive monitoring of gas exchange. This can be useful in a patient who has alveolar hypoventilation, to accurately assess the extent of CO 2 retention, or in a patient who has sickle cell disease with abnormal hemoglobin, in whom the pulse oximetry may not accurately reflect arterial oxygen level .
Begin the review
It is helpful to preview the physician note/orders before the study to determine why the PSG is being performed. This will help ensure that the question being posed by the ordering physician will be appropriately addressed. For example, if a child is being studied to determine whether he/she can tolerate having his/her tracheostomy tube capped, it is important to make certain the child has the capping device, and that the technicians know that the tracheostomy is to be capped during the study. Before beginning review of the study, it is helpful to review any notes made by the technician during the course of the night. This alerts the physician to technical or patient issues encountered over the course of the study. These issues might include unusual events over the night, such as confusional arousals or artifactual desaturation related to patient compromise of the oximeter probe. In general, polysomnograms (PSGs) should be reviewed and scored by an experienced scoring technician before interpretation; however, all PSGs should be examined page by page by the reviewing professional for the most accurate interpretation of the nocturnal events.
First, the biocalibration should be evaluated. This is a series of tests conducted by the technician at the beginning and end of the study to document the normal function of the various channels of information recorded. The biocalibration may be limited in children who are young, developmentally delayed, or uncooperative. The components of the biocalibration include having the patient look up, down, and to both sides in order to assess detection of eye movements by EOG, which facilitates scoring of REM sleep. The EEG is evaluated with eyes open and closed in order to identify alpha EEG waves, which aid in detection of wakefulness. The patient is asked to make a snoring type noise to check the snore channel, and the patient is asked to grit his/her teeth to detect bruxism. The patient moves both legs separately to assess the integrity of the leg EMGs. The patient is asked to hold his/her breath to detect cessation of chest wall movement, and the chest and abdomen belts are tested to make certain they move together with respiratory effort.
Sleep stage analysis
It is helpful to quickly review the patient’s sleep architecture by viewing the hypnogram ( Fig. 1 ). A hypnogram is a summary of the different sleep stages achieved shown in graphic form. It is important to review the sleep architecture in terms of what is to be expected for the patient’s age. Timing and length of various sleep stages vary with patient age, and should be compared with age-expected norms. For example, although it is normal for infants to enter sleep through stage REM, entering sleep through stage REM may suggest an underlying sleep disorder such as narcolepsy in an older child or adolescent.
