Otolaryngol Clin N Am

40 (2007) 745–759

Interpretation of the Polysomnogramin Children

Mary H. Wagner, MD*, Daniel M. Torrez, MDDepartment of Pediatrics, Division of Pediatric Pulmonary, University of Florida,

1600 SW Archer Road, Gainesville, FL 32610, USA

Polysomnography (PSG) is important in the evaluation of nocturnalevents in children as well as adults. Events that can be evaluated includeobstructive sleep apnea syndrome (OSAS), periodic leg movements(PLM), nocturnal seizures, parasomnias, and issues related to nocturnalgas exchange. This article discusses the use of PSG primarily in terms ofrespiratory events, leg movements, and gas exchange problems in children.

PSG has been recommended to evaluate several conditions in children,including [1]

� Differentiation of benign from pathologic snoring� Disrupted sleep� Excessive daytime sleepiness� Unexplained failure to thrive� Cor pulmonale� Polycythemia� Laryngomalacia in children when worsened with sleep� Underlying disorders predisposing children to nocturnal hypoxemia orhypoventilation, such as bronchopulmonary dysplasia, cystic fibrosis,neuromuscular disorders (muscular dystrophy, spinal muscular atrophy,cerebral palsy, or congenital muscle diseases)� Suspected alveolar hypoventilation� Confirmation of clinical diagnosis of airway obstruction suggested bysymptoms including apnea, paradoxical respirations, or increasedwork of breathing� Documentation of severity of obstructed breathing to guide therapeuticintervention and identification of those at increased risk of postopera-tive complications

* Corresponding author.

E-mail address: wagneam@peds.ufl.edu (M.H. Wagner).

0030-6665/07/$ - see front matter � 2007 Published by Elsevier Inc.

doi:10.1016/j.otc.2007.04.004 oto.theclinics.com

746 WAGNER & TORREZ

� Titration of positive pressure for medical treatment of OSAS� Follow-up evaluation of children who have persistent symptoms postin-tervention for OSAS

Sleep disordered breathing (SDB) is a common cause of morbidity inchildhood, with a spectrum ranging from benign snoring to complete airwayobstruction. Benign or primary snoring is reported in 3% to 12% of thepediatric population, with OSAS affecting 1% to 3% [2]. Several authorshave demonstrated that clinical history and physical examination are notaccurate in the identification of children who have OSAS [3]. PSG is usefulin documenting the presence of obstructive sleep apnea (OSA) events as wellas their severity. PSG has been recommended as the test of choice toevaluate SDB by consensus of a panel of experts [4]. PSG has also shownto be useful in determining readiness for decannulation in children whohave tracheostomy [5].

Performance of polysomnography in children

PSG should be performed by a laboratory experienced in and comfort-able with caring for children [1]. Technicians need to be experienced in deal-ing with children of various age levels and developmental status. Personnelshould be certified in pediatric cardiopulmonary resuscitation. If a dedicatedpediatric facility is not available, an area in the adult sleep laboratory shouldbe designated for children. Children should be housed in an appropriateenvironment, with accommodations for a caregiver to sleep near the child.Caregiver availability to the child is important to minimize the child’sanxiety 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 personnelskilled in the presentation of medical information. A crib should beavailable for small children. The person responsible for supervision of thepediatric sleep facility or functions should be a pediatrician with trainingand expertise in the area of sleep medicine. This person must assure thatthe PSG performance, scoring, and interpretation are appropriate for theage and condition of the child.

The study timing should be set to mimic the child’s bedtime as closely aspossible. Overnight studies are preferred because negative nap studies havebeen shown not to exclude the possibility of OSAS during a night study [6].Studies should be performed without sedation in order to most accuratelymimic the child’s normal sleep.

Components of polysomnography in children

Variables gathered during PSG in children are similar to those obtainedin adults, with some additional information. Children may often demon-strate obstructive hypoventilation as a component of their OSAS, which

747INTERPRETATION OF THE POLYSOMNOGRAM IN CHILDREN

may only be detected by increased carbon dioxide (CO2) levels [7]. Thus,PSG monitoring in children should include some method of determiningCO2 levels, such as end tidal CO2 or transcutaneous CO2 [8]. The manychannels of physiologic parameters and their purpose in the PSG aredescribed in the following sections [1].

Sleep stages are determined using electroencephalogram (EEG), chinelectromyogram (EMG), and electro-oculogram (EOG). EEG monitoringincludes two central and two occipital leads with references to the oppositeposterior auricular area. Additional EEG leads can be used to detect noctur-nal events such as seizure activity. Three chin EMG leads are placed andused to detect skeletal muscle activity as required for the identification ofrapid eye movement (REM) sleep. The chin EMG is also useful to detectswallowing and sucking during the study. Right and left EOG leads areused to detect eye movements essential to the identification of REM sleep.

Respiratory effort is detected using chest and abdominal belts. Differentstyles of monitoring include strain gauges, chest wall impedance, inductanceplethysmography, intercostal EMG, and pneumatic transducers [9]. Thesebelts can assess qualitative respiratory effort, which is essential to distin-guishing whether respiratory events are central or obstructive in origin.Air entry is assessed using a thermistor, nasal pressure, and a capnographtracing. The thermistor detects airflow at the nose and mouth by detectinga temperature change in expired gas. Nasal pressure is an additional methodof monitoring airflow by detecting pressure changes via a cannula placed inthe nose. A recent study showed that the nasal pressure transducer is moresensitive in the detection of hypopnea, and suggested combining the use ofboth the thermistor and nasal pressure transducer for optimal detection ofSDB in children [10]. During positive pressure titrations, flow is detectedusing measurements from the positive pressure device.

Movements of extremities are monitored by EMG leads placed on thelegs and sometimes on the arms. These movements are important in docu-menting PLM as well as movements that result from respiratory events.Position sensors can be used to document patient position. Digital videois also obtained. The video is useful in documenting patient position, move-ments, and unusual episodes such as parasomnias. Snoring is assessed bya snore microphone placed on the neck of the patient, by technicianobservation, and by audio recording.

Gas exchange is assessed using monitoring for both oxygen and CO2.Oxygenation is monitored by pulse oximetry, using a comfortable sensorthat can be left on the child for the duration of the study. It is essentialthat the pulse oximeter have a short sampling time (2 to 3 seconds) to avoidmissing brief desaturations associated with events in children. The reliabilityof the pulse oximeter tracing is improved with recording of the pulse ampli-tude signal, allowing identification of desaturation events that are caused bypoor probe function [11]. Ventilation is monitored in children by either endtidal (ET) CO2 or transcutaneous CO2 monitoring. The ET CO2 method is

748 WAGNER & TORREZ

more responsive to rapid changes, whereas the transcutaneous method is notreflective of transient CO2 changes, and is most useful for a trend [8,12]. ETCO2 is monitored by a probe placed at the nose and mouth. ET CO2 gener-ates a flow tracing that can also be used to monitor airflow. The sensor forthe transcutaneous device must be changed every several hours to maintainaccuracy. In patients with persistent gas exchange abnormalities, access toarterial blood gas measurement is useful in corroborating noninvasive mon-itoring of gas exchange. This can be useful in a patient who has alveolarhypoventilation, to accurately assess the extent of CO2 retention, or ina patient who has sickle cell disease with abnormal hemoglobin, in whomthe pulse oximetry may not accurately reflect arterial oxygen level [13].

Begin the review

It is helpful to preview the physician note/orders before the study todetermine why the PSG is being performed. This will help ensure that thequestion being posed by the ordering physician will be appropriatelyaddressed. For example, if a child is being studied to determine whetherhe/she can tolerate having his/her tracheostomy tube capped, it is importantto make certain the child has the capping device, and that the techniciansknow that the tracheostomy is to be capped during the study. Before begin-ning review of the study, it is helpful to review any notes made by the tech-nician during the course of the night. This alerts the physician to technical orpatient issues encountered over the course of the study. These issues mightinclude unusual events over the night, such as confusional arousals or arti-factual desaturation related to patient compromise of the oximeter probe. Ingeneral, polysomnograms (PSGs) should be reviewed and scored by anexperienced scoring technician before interpretation; however, all PSGsshould be examined page by page by the reviewing professional for themost accurate interpretation of the nocturnal events.

First, the biocalibration should be evaluated. This is a series of tests con-ducted by the technician at the beginning and end of the study to documentthe normal function of the various channels of information recorded. Thebiocalibrationmay be limited in children who are young, developmentally de-layed, or uncooperative. The components of the biocalibration include hav-ing the patient look up, down, and to both sides in order to assess detection ofeye movements by EOG, which facilitates scoring of REM sleep. The EEG isevaluated 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 snoringtype noise to check the snore channel, and the patient is asked to grit his/herteeth to detect bruxism. The patient moves both legs separately to assess theintegrity of the leg EMGs. The patient is asked to hold his/her breath todetect cessation of chest wall movement, and the chest and abdomen beltsare tested to make certain they move together with respiratory effort.

749INTERPRETATION OF THE POLYSOMNOGRAM IN CHILDREN

Sleep stage analysis

It is helpful to quickly review the patient’s sleep architecture by viewingthe hypnogram (Fig. 1). A hypnogram is a summary of the different sleepstages achieved shown in graphic form. It is important to review the sleeparchitecture in terms of what is to be expected for the patient’s age. Timingand length of various sleep stages vary with patient age, and should be com-pared with age-expected norms. For example, although it is normal forinfants to enter sleep through stage REM, entering sleep through stageREM may suggest an underlying sleep disorder such as narcolepsy in anolder child or adolescent.

Components of sleep architecture that should be assessed include:percentage of total sleep time (TST) spent in stage I/II, stage III/IV, stageREM, and wakefulness. These percentages should be compared with age-appropriate normals. Several authors have examined sleep architecture innormal children ages 1 to 15 years [14–18]. In these studies, stage I sleep oc-cupied 4% to 7.7% of TST, and stage II occupied 36% to 49% of TST, withthe combination of stage I and II in each study ranging from 41% to 53% ofthe TST. Slow wave sleep (combining stages III and IV) occupied 14% to32% of the TST, whereas stage REM occupied 17.4% to 21.1% of the TST.

Fig. 1. This is a typical hypnogram showing time across the bottom axis. The left axis shows the

different sleep stages. The horizontal bars indicate the time spent in the various sleep stages

during the course of the PSG.

750 WAGNER & TORREZ

Timing of sleep stages can be noted by review of the hypnogram. Chil-dren usually have a short period of stage I/II after sleep onset, and thenenter stage III/IV (also known as delta or slow wave sleep). Stage III/IVsleep will predominate early in the night, with regular cycling between thestages I/II, stages III/IV, and REM. REM sleep will usually cycle every60 to 120 minutes, with a wide range of timing between REM periods [14].

Sleep latency, the time after lights out until sleep is achieved, should alsobe noted. Sleep latency is generally less than 25 minutes [14,16]. It may beprolonged if the child has recently had a nap, and it may be shortened incertain sleep disorders. Sleep efficiency is a measurement of the amount ofthe total time in bed that the patient spends asleep, and should also benoted. It gives a picture of whether the patient has a disrupted sleep pattern.Sleep efficiency in children is usually greater than 89% [14–18].

REM latency, the time from onset of sleep to the first epoch of REMsleep, is also noted. REM latency can be prolonged if the first REM periodis difficult to detect by the scoring technician. REM latency can be shortenedin certain conditions, such as depression or narcolepsy. The presence andamount of REM sleep deserves careful attention. Length of time spent inREM is short earlier in the night, with lengthening of REM episodes asthe night progresses [14]. During REM sleep, OSA may be worsenedbecause of loss of muscle tone. Thus, to make certain the most severe extentof OSA is observed, patients should achieve REM sleep. REM sleep may bedecreased if the patient has a disrupted sleep pattern, with arousals out ofREM caused by obstructive events. This may cause the overall number ofobstructive events to be lowered.

EEG should be monitored for unusual complexes, such as nocturnalepileptiform discharges (Fig. 2). These may be noted in children who havea history of a seizure disorder as well as in those who do not have such a his-tory. Whether these episodes are associated with clinical seizure activity orrespiratory events should be noted. Technician observation and the videoshould be reviewed for evidence of clinical seizure activity in associationwith these EEG changes. Consideration may be given to a more thoroughevaluation by a full sleep-deprived EEG if complexes are widespread duringthe recording.

Arousal summary

Arousals are scored by the scoring technician based on the appearance ofthe EEG tracing. An arousal is scored when there is an abrupt change in theEEG lasting 3 seconds, following at least 10 seconds of continuous sleep[19]. Arousals can be attributed to preceding events, including respiratoryevents, leg movements, snore events, or technician presence in the room,or may occur without an obvious trigger. Arousals are reported using thearousal index, which is the number of arousals divided by the hours of sleep.Normal values for arousal indices vary from laboratory to laboratory.

751INTERPRETATION OF THE POLYSOMNOGRAM IN CHILDREN

Studies of normal children have found mean arousal indices of 8.8 to 9.5[14,15,17]. Arousals attributed to respiratory events give a measure of sleepdisruption caused by those respiratory events. It is also important to notethat children may not arouse to respiratory events as easily as adults do [7].

Heart rate/rhythm

The ECG should be reviewed for evidence of brady or tachy rhythms aswell as abnormal ECG rhythms. Respiratory events may be associated withdecrease in heart rate, with subsequent increase in heart rate after the eventhas resolved, or in association with arousals. Some patients will haveevidence of premature ventricular or atrial contractions, which may ormay not be related to respiratory events.

Snoring

Determination of the presence or absence of snoring is important to note,particularly in comparison to what is observed in the home environment. Ifa child has loud snoring over the course of the night, typical to what parentsdescribe at home, with few documented respiratory events, a diagnosis of

Fig. 2. Shown here is an episode of spike and wave activity occurring out of stage II sleep. The

tracing shows the EEG leads on the left axis with time on the bottom axis. A 10-second duration

screen is shown, with each rectangle along the bottom axis representing 1 second.

752 WAGNER & TORREZ

primary snoring may be made. This may be reassuring to family members,in that the snoring they have noted at home is not associated with docu-mented respiratory events or gas exchange abnormalities; however, thereare reports in the literature that snoring without respiratory events hasbeen associated with poor academic performance [20,21].

Leg movements

The scoring technician will score leg movements that meet criteria forPLM. Criteria for PLM include leg movements noted in either or bothlegs that are at least one quarter of the amplitude noted during the biocali-bration lasting from 0.5 to 5 seconds. Leg movements must be separated byat least 5 seconds, but not more than 90 seconds, and must occur in clustersof at least four to be considered PLM (Fig. 3). These leg movements shouldnot be related to other events, such as respiratory events or arousals [22].Leg movements should be carefully reviewed to make certain they meetcriteria for PLM and are not related to subtle respiratory events. The totalnumber of PLM that meet these criteria are determined, and the PLM indexis calculated by dividing the total number of PLM by the number of hoursof sleep. A PLM index of five or greater is considered abnormal [22,23].

Fig. 3. This tracing shows a series of four periodic leg movements occurring over a time span of

2.5 minutes. The PLM are apparent as deflections in the two leg channels. LAT refers to left

anterior tibialis and RAT refers to right anterior tibialis. These leg movements are not associ-

ated with respiratory events or arousals.

753INTERPRETATION OF THE POLYSOMNOGRAM IN CHILDREN

Respiratory events

Several definitions are important for the classification of respiratoryevents. The term ‘‘apnea’’ refers to an event with no flow. Apneas are scoredfor events with a decrease in flow by 75% or greater from the baseline flowobserved before the event. If any portion of an event fits this definition, theevent can be scored as an apnea. Hypopnea refers to a decrease in flow by30% to 50% from the usual baseline. Apneas and hypopneas can be furtherclassified as being central, obstructive, or mixed in nature.

Obstructive events are those caused by a decrease in flow associated withpersistent, sometimes increased respiratory effort noted in the chest andabdominal belts. Obstructive apneas are scored when a decrease of 75%or greater is detected in the airflow or nasal pressure channels associatedwith continued respiratory effort (Fig. 4) [24]. Whereas in adults there isa 10-second minimum event length noted, in children the events must betwo respiratory cycles [25]. Thus, in an infant breathing at 60 times per min-ute, a significant event can be as brief as 2 seconds. An obstructive hypopneais scored when a decrease in the flow channel of 30% to 50% is noted withpersistent respiratory effort (Fig. 5) [1,25]. In order for an obstructive hypo-pnea to be scored, there must be some consequence to the event, includinga 3% to 4% drop in oxygen saturation, a leg movement, or an EEG arousal.

Fig. 4. This figure demonstrates two episodes of obstructive apnea shown by cessation of flow

in the nasal pressure and airflow channels with continued respiratory effort. The events result in

oxygen desaturation as low as 80%.

754 WAGNER & TORREZ

The contour of the nasal pressure tracing is often flattened, indicating flowlimitation with respiratory effort during obstructive hypopneas [26].

Central events are those caused by an absence or severe decrease in respi-ratory effort, as measured by chest or abdominal belts. Central apneas(Fig. 6) are scored when there is an absence of respiratory effort associatedwith a 70% or greater decrease in the airflow or nasal pressure. Duringcentral apneas, there may be small deflections noted in the chest tracing cor-responding to cardioblastic artifact from chest wall movement associatedwith cardiac activity. Central hypopneas (Fig. 7) are events with decreasedrespiratory effort associated with a 30% to 50% decrease in the airflow ornasal pressure channels and desaturation or EEG arousal. The contour ofthe nasal pressure tracing will be rounded during central hypopneas, com-pared with the flattened contour noted with obstructive hypopneas [26]. Itis important to be certain that central hypopneas are not confused withobstructive hypopneas. Obstructive hypopneas may appear to be associatedwith an apparent decrease in respiratory effort caused by work against anobstructed upper airway [26]. Central events are more likely to be notedduring REM sleep, particularly in patients who have underlying disorderssuch as Prader-Willi syndrome or Arnold-Chiari malformation. Mixed

Fig. 5. An episode of obstructive hypopnea is shown here, depicting two epochs or 1 minute of

a PSG. The event is marked by a decrease in the nasal pressure and airflow with continued re-

spiratory effort. The hypopnea results in a drop in oxygen saturation to 94% and an EEG

arousal.

755INTERPRETATION OF THE POLYSOMNOGRAM IN CHILDREN

respiratory events are those with a central and obstructive component.Usually, these events begin with the central component, then progress toan obstructed component with the resumption of respiratory effort.

After all events are reviewed and scored, several indices can be calculated.These include apnea index (AI) and apnea-hypopnea index (AHI) which arecalculated for the entire sleep period, for non-REM (NREM) and REMsleep. The term ‘‘index’’ refers to the number of events divided by the num-ber of hours of sleep. This calculation allows the comparison of PSGs ofvarious lengths. The AI is determined using only apneas; the AHI includesapneas and hypopneas.

Studies of normal children suggest that any obstruction is abnormal, andthat normal values for children are different from those for adults. Severalauthors have investigated PSG findings in normal children [14,15,17]. Thereis general agreement that AI and AHI are less than 1 in normal children.Katz and Marcus [2] have suggested the following values for classificationof respiratory events in children:

� AHI less than 1 ¼ normal� AHI 1 through 4 ¼ mild OSA� AHI 5 through 10 ¼ moderate OSA� AHI greater than 10 ¼ severe OSA

Fig. 6. This tracing demonstrates a central apnea lasting 11.5 seconds, resulting in a drop in

oxygen saturation to 91% and an EEG arousal. During this event there is cessation of airflow

with lack of respiratory effort.

756 WAGNER & TORREZ

They also propose grading of disease severity by gas exchange parame-ters. The AHI should be considered in the context of the patient’s presenta-tion. Children who have complications of OSAS or underlying medicalproblems may require intervention for mild OSA in order to prevent wors-ening of their medical disorder or worsened complications. For example,children who have pulmonary hypertension might require aggressive inter-vention, despite mild OSA, to prevent worsening of their pulmonaryhypertension.

Gas exchange

Gas exchange should be reviewed carefully for the entire tracing. Thepulse oximetry tracing should be reviewed for desaturation, with carefulattention to whether the desaturation is associated with a respiratory event,arousal, or leg movement. Desaturations might be caused by respiratoryevents of any duration. The actual desaturation will occur 1 to severalseconds after the respiratory event. If the respiratory event is prolonged,the desaturation may begin before the event has terminated. Desaturationsunassociated with respiratory events should be reviewed for accuracy in

Fig. 7. This tracing demonstrates a 2-minute window in REM sleep with two episodes of cen-

tral hypopnea. These events are marked by a decrease of at least 30% in the airflow channel,

with a concomitant decrease in respiratory effort in the chest and abdomen channels. These

events result in significant oxygen desaturation as low as 78% and increase in ETCO2 to 53 torr.

757INTERPRETATION OF THE POLYSOMNOGRAM IN CHILDREN

terms of whether the pulse oximeter is tracing accurately, or whether thepulse oximetry probe has been compromised by patient position. It is impor-tant to note the baseline oxygen saturation before study onset. Patients whohave low saturation at baseline may be at risk for desaturation with sleeponset, worsening with respiratory events. Those who have persistent oxygendesaturation without respiratory events potentially require further investiga-tion for underlying lung disease, hypoventilation, or abnormal hemoglobin(ie, sickle cell disease). Hypoventilation can be evaluated by noting the CO2

associated with episodes of oxygen desaturation. In general, oxygen satura-tion should be greater than 92% in normal studies [14,15,17,18,27]. Childrenon oxygen supplementation should have their flow rate recorded at thebeginning of the study, with monitoring of response to changes in theoxygen flow rate over the course of the study.

CO2 tracing should be reviewed as well. Baseline CO2 level before sleeponset should be noted. Normal children can be expected to have a 5 to 7torr rise in CO2 with sleep onset [27]. Children may have a pattern of ob-structive hypoventilation with OSAS, resulting in increases in CO2 withoutsignificant oxygen desaturation. Abnormal levels of CO2 vary, with Marcusand colleagues [27] reporting greater than 10% of TST being spent with CO2

greater than 50 torr as abnormal, and Montgomery-Downs and colleagues[14] reporting that in normal children, 2.8 � 11.3 of the TST was spent witha CO2 greater than or equal to 50 torr. Marcus and colleagues [27] alsoreport CO2 levels of greater than 53 torr as being abnormal. Uliel and col-leagues [18] found less time spent with CO2 greater than 45 torr in theirstudy of normal children, suggesting that ET CO2 greater than 45 torr forgreater than 10% of the TST, or any CO2 greater than 50 torr, is abnormal.It is important to recognize potential issues associated with ETCO2 moni-toring. Sampling tubing can become obstructed with nasal secretions ormoisture, and may become displaced. Other factors that affect the accuracyof the ETCO2 readings include mouth breathing, airway obstruction,supplemental oxygen delivery at the other nostril, and cyanotic heart disease[28–30]. It is important to know the values obtained in your individual sleeplaboratory, and compare values during the study with the baseline values.CO2 trends may be more helpful, with consideration given to obtaininga blood gas for high values to determine the accuracy of noninvasivemeasurements.

Summary

PSG in children represents an important and useful tool in the evaluationof the multitude of sleep-related conditions, including OSAS, PLM disorder,and those with an underlying predisposition toward gas exchange aber-rancies. To obtain the most useful information, sleep studies in this uniquepopulation should be performed in laboratories with staff experienced in

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working with children of all ages and stages of development, in a setting sen-sitive to both child and caregiver.

In performing pediatric PSG, physicians should keep in mind

PSG can be successfully performed in children.Pediatric PSG should be performed in a laboratory experienced in and

comfortable with the care of children.Recognize that PSG in children includes measurement of carbon dioxide

levels to detect obstructive or central hypoventilation.Criteria for scoring and interpretation of PSG in children differ from

those for adults.

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