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Volume 14 No. 12
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Accepted Papers





Scientific Investigations

The Accuracy of an Ambulatory Level III Sleep Study Compared to a Level I Sleep Study for the Diagnosis of Sleep-Disordered Breathing in Children With Neuromuscular Disease

Haley Fishman, MD, FRCPC1,2; Colin Massicotte, RPSGT1; Rhonda Li, RPSGT1; Weeda Zabih, MD1,2; Laura C. McAdam, MD, FRCPC, MSc1,2,3; Suhail Al-Saleh, MBBS, FRCPC, MSc1,2; Reshma Amin, MD, FRCPC, MSc1,2
1Division of Respiratory Medicine, The Hospital for Sick Children, Toronto, Ontario, Canada; 2University of Toronto, Toronto, Ontario, Canada; 3Division of Developmental Pediatrics, Holland Bloorview Kids Rehabilitation Hospital, Toronto, Ontario, Canada

ABSTRACT

Study Objectives:

Polysomnography (PSG) surveillance recommendations are not being met for children with neuromuscular disease (NMD) because of limited diagnostic facilities. We evaluated the diagnostic accuracy of an ambulatory level III device as compared to a level I PSG.

Methods:

A cross-sectional study was conducted at a tertiary pediatric institution. Eligibility criteria included: (1) children with NMD; (2) age 6 to 18 years; (3) booked for a clinically indicated overnight level I PSG. Participants were randomized to an overnight level I PSG followed by an ambulatory level III study with end tidal carbon dioxide (etCO2) or vice versa. Sensitivity and specificity of the ambulatory level III device to diagnose sleep-disordered breathing (SDB) at an apnea-hypopnea index (AHI) cutoff of > 1.0 events/h was the primary outcome.

Results:

Moderate to severe SDB was found in 46% of participants (13/28). The device's sensitivity and specificity to detect SDB was 61.5% and 86.7%, respectively. The positive predictive value of the level III study was 80.0% and the negative predictive value was 72.0%. Fifty percent of the cohort were either missing or had incomplete or falsely low ambulatory etCO2 data.

Conclusions:

A level III device with etCO2 is not yet able to be implemented in clinical practice as a diagnostic tool for SDB in pediatric patients with NMD.

Commentary:

A commentary on this article appears in this issue on page 1973.

Citation:

Fishman H, Massicotte C, Li R, Zabih W, McAdam LC, Al-Saleh S, Amin R. The accuracy of an ambulatory level III sleep study compared to a level I sleep study for the diagnosis of sleep-disordered breathing in children with neuromuscular disease. J Clin Sleep Med. 2018;14(12):2013–2020.


BRIEF SUMMARY

Current Knowledge/Study Rationale: Children with neuromuscular disease (NMD) are at a significant risk for sleep-disordered breathing (SDB). There is a paucity of sensitive and specific diagnostic tests to evaluate for the presence SDB. A level I polysomnography is the gold standard test. If diagnostically accurate, an ambulatory level III device could help manage the lengthy waiting lists for level I polysomnography.

Study Impact: We have shown that a level III device with end-tidal capnography has poor diagnostic accuracy to diagnose SDB in children with NMD. A level III device with end-tidal capnography should not yet be implemented in clinical practice as a diagnostic tool for SDB in children with NMD.

INTRODUCTION

Children with neuromuscular disease (NMD) are at a significant risk for sleep-disordered breathing (SDB). SDB is a broad term, encompassing abnormalities in respiratory pattern, gas exchange, and sleep architecture during sleep.1 The prevalence of SDB in pediatric patients with neuromuscular disease is estimated to be greater than 40%, a tenfold greater occurrence than in the general population.2 Progressive neuromuscular weakness leads to hypoventilation, upper airway obstruction, secretion retention, and scoliosis.3 In addition, obesity secondary to limited mobility and/or steroid use as well as craniofacial anomalies such as macroglossia and retrognathia further worsen the risk of SDB in children with NMD.2

There are several systemic effects of untreated SDB resulting in a reduction in health-related quality of life and increased healthcare resource utilization.4 The initiation of ventilatory support in children with NMD has been shown to reduce hospital admissions and prolong survival.3

Clinical symptoms are poor predictors of SDB in children with NMD and pulmonary function test cutoffs have limited sensitivity and specificity to predict SDB.57 Therefore, international societies have recommended surveillance polysomnography (PSG) in a large proportion of children with NMD.3,8 Unfortunately, these recommendations are not feasible in many parts of the world given the limited number of pediatric sleep diagnostic facilities.2,913 The long wait list for PSG tests is a significant concern, especially in children given the sequelae of untreated SDB. Several attempts have been made to find screening tools for SDB in children, but there has been limited success.1417

It has been internationally recognized that there is a need for pediatric level III studies, an unattended sleep study with limited channels (four to seven channels) conducted in the home.18 This approach has been implemented with success in adults but a gold standard ambulatory level III device for diagnosing SDB in children does not yet exist.19 An effective ambulatory level III device for the NMD population would be able to identify obstructive and central sleep apnea as well as hypoventilation. The ambulatory level III device could then be used to triage children on existing PSG waiting lists and facilitate screening of all patients with NMD as per recommended guidelines. The numbers of children with NMD requiring surveillance PSGs is only going to increase given the recent approval of disease-modifying drugs such as nusinersen (Spinraza).20,21 Our study aim was to evaluate the diagnostic accuracy of an ambulatory level III device as compared to level I PSG in children with NMD at risk of SDB.

METHODS

This prospective, cross-sectional study took place at the Hospital for Sick Children, a tertiary pediatric institution in Toronto, Ontario, Canada. Patients were recruited from the Long-term Ventilation and Sleep Medicine clinics from March 1, 2015 to January 31, 2017. Inclusion criteria were as follows: (1) children with a confirmed diagnosis of NMD; (2) children age 6 to 18 years; (3) booked for a clinically indicated overnight level I PSG. The aforementioned age cutoff was chosen because it is the age at which most patients are able to perform pulmonary function tests.22 Exclusion criteria were as follows: (1) a known diagnosis of or previous treatment for SDB; (2) current use of supplemental oxygen, noninvasive positive pressure ventilation (NiPPV) or invasive mechanical ventilation at home; (3) initiation of supplemental oxygen and/or NiPPV during the PSG; (4) concurrent upper respiratory tract infection. Institutional approval was obtained from the Research Ethics Board (REB # 1000038443) at the Hospital for Sick Children.

Patients were screened for eligibility during a regularly scheduled clinic visit. After informed consent was obtained, demographic and clinical data were collected. All study participants were randomized to either an overnight level I PSG followed by the ambulatory level III study or vice versa. All level I and level III studies were performed within 2 weeks of each other.

The demographic and clinical data collected from study participants included the following: age, sex, height, weight, body mass index (BMI), primary diagnosis, comorbidities, and pulmonary function test results.

All patients underwent standard overnight level I PSG in the sleep laboratory at the Hospital for Sick Children, using a data acquisition and analysis system (XLTEK, Natus Medical Inc, United States). The PSG montage included electroencephalogram, electrooculogram, and submental and bilateral anterior tibialis electromyograms as well as audio and video recordings. Respiratory measurements included QRIP respiratory inductive plethysmography, pressure transducer and thermistor by Braebon (Braebon Medial Corporation, Canada). Oxygen saturation was measured using an oximeter (Masimo Corporation, United States), transcutaneous carbon dioxide (tcCO2) using SenTec (Therwil, Switzerland) and end-tidal carbon dioxide (etCO2) was recorded using capnography (Capnocheck Sleep, BCI, United States).23 Sleep architecture was assessed using standard techniques.24

Information obtained from PSG included sleep onset latency and rapid eye movement onset latency, total sleep time (TST), sleep efficiency, time spent in each sleep stage (minutes and percentage), number and classification of arousals, number of independent leg movements and snoring. Recorded respiratory data included counts and indexes of the following events: obstructive apneas, obstructive hypopneas, central apneas, central hypopneas, and mixed apneas.

All events were scored according to The AASM Manual for the Scoring of Sleep and Associated Events: Rules, Terminology and Technical Specifications (AASM Scoring Manual) version 2.325 scoring guidelines for children by a registered polysomnographic technologist who was blinded to the results of the level III ambulatory study.25 An obstructive apnea event was scored when airflow decreased > 90% from baseline for at least 90% of the entire respiratory event with chest and/or abdominal motion throughout the entire event; the duration of the event was at least a minimum of two baseline breaths.25 An obstructive hypopnea event was scored when airflow dropped by at least 30% from baseline, the duration of which was at least a minimum of two baseline breaths and the event was accompanied by a minimum 3% drop in oxygen saturation, an arousal, or an awakening. A central apnea event was defined as a cessation of airflow with an absence of respiratory and abdominal effort for a minimum of 20 seconds or the duration of at least two baseline breaths, in which case the event was accompanied by a minimum 3% drop in oxygen saturation, an arousal, or an awakening. A central hypopnea event was scored when airflow dropped by at least 30% from baseline, the duration of which was at least a minimum of two baseline breaths, absence of snoring, respiratory and abdominal effort, and a minimum 3% drop in oxygen saturation, an arousal, or an awakening. Hypoventilation was scored during sleep when > 25% of the total sleep time was spent with a CO2 > 50 mmHg, as measured by tcCO2 or etCO2.25

SDB severity was graded according to accepted clinical criteria.24 The obstructive apnea-hypopnea index (OAHI) was the number of obstructive apneas, mixed apneas, and obstructive hypopneas per hour during sleep. The central apnea-hypopnea index (CAHI) was the number of central apneas and central hypopneas per hour during sleep. An apnea-hypopnea index (AHI) ≤ 1 event/h was considered to be normal, an AHI from > 1 to < 5 events/h was considered to be mild SDB, an AHI from 5 to < 10 events/h was considered to be moderate SDB, and an AHI ≥ 10 events/h was considered to be severe SDB. Minimum criteria for acceptable recordings included at least 4 hours of respiratory effort signals with concurrent reliable oximetry data.26

The NOX-T3 (Nox Medical, Iceland and distributed by Care Fusion, Yorba Linda, California, United States), ambulatory sleep acquisition device (level III) is a multichannel tool designed to screen for SDB. It is the first level III device developed for a pediatric population. Furthermore, it is the first pediatric level III device that is able to monitor etCO2 by interfacing with the Respisense end tidal carbon dioxide monitor (Nonin Medical, Plymouth, Minnesota, United States). The channels used in this device include: nasal airflow and etCO2 via a dual nasal cannula, respiratory belts, pulse oximetry, heart rate, audio, and position. The level III device was mailed to patients after they had been shown how to use the equipment during the clinic visit. Caregivers were encouraged to intermittently monitor their child during the night to ensure the device remained correctly in place. A priori, our established criteria to exclude level III data was as follows: (1) signal quality indicator less than 50% (determined by the level III device based on the duration of artefact and signal dropout); (2) estimated sleep time less than 4 hours; (3) missing oxygen saturation recording; (4) missing air flow signal.

The computer-generated scoring provided by the ambulatory level III device was not used. All ambulatory level III studies were scored by a registered polysomnographic technologist in accordance with the AASM Scoring Manual version 2.3 for the channels of data that were available.24 Following the use of the ambulatory level III device, patients were requested to complete an Ambulatory Sleep Device Usability Questionnaire (see supplemental material).

The level I PSG and ambulatory level III studies were scored by a PSG technologist, blinded to the scoring results of the other tests (R.L.). One sleep physician (R.A.) reported all of the PSG tests and communicated the results to the patients and families. The physician was blinded to the results of the ambulatory level III study at the time the level I PSG tests were reported.

The primary outcome of our study was the sensitivity and specificity of the ambulatory level III device to diagnose SDB at an AHI cutoff of ≥ 1 event/h. The secondary outcome of our study was the sensitivity and specificity of the ambulatory level III device to diagnose SDB at an AHI cutoff of ≥ 5 events/h.

Statistical Analysis

Descriptive statistics were used to summarize the baseline demographics, medical history, and level I PSG and ambulatory level III study results. For normatively distributed continuous variables, mean and standard deviation were calculated. For non-normatively distributed continuous variables, median and interquartile range were calculated. Normality was determined using the Shapiro-Wilk normality test. Frequencies were presented for categorical data. Sensitivity, specificity, and positive and negative predictive values for the manually scored ambulatory level III study was calculated using AHI cutoff values of ≥ 1 event/h and ≥ 5 events/h. Correlations between the AHI obtained from the level I study and the manually scored level III study were determined using Spearman correlation coefficient. TST for the level III study was manually calculated by multiplying the percent sleep efficiency by the total time in bed. A minimum sample size of 25 was needed to detect a correlation coefficient of .50, with a two-tailed α = .05 and β = .10. Statistical significance was set at P < .05. All analyses were performed using SAS version 9.3 (SAS statistical software, Cary, North Carolina, United States).

RESULTS

A total of 32 patients were enrolled in the study, of which complete data for the level I PSG and level III studies were available for 28 patients (88%). Of the 4 patients not included, 1 patient did not tolerate the level I PSG and the other 3 patients had level III studies that did not meet the a priori acceptability criteria.

A total of 28 patients were included in the study. Patient demographics are summarized in Table 1. The median (interquartile range [IQR]) age of the study cohort was 14.5 (IQR 10.5, 16.0) years. Nineteen (67.9%) of the participants were male. The most common NMD diagnosis was Duchenne muscular dystrophy (DMD) (n = 12, 42.9%). The median (IQR) BMI percentile was 82.5 (9.8, 93.7).

Baseline characteristics of the study participants (n = 28).

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Table 1

Baseline characteristics of the study participants (n = 28).

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Level I PSG Study Results

Of all the patients who had a level I study, 13 of 28 patients (46.4%) had moderate to severe SDB, defined as an OAHI > 5 events/h, CAHI > 5 events/h, and/or hypoventilation. In the study cohort, 9 patients (32.1%) had mild obstructive sleep apnea (OSA), 5 patients (17.9%) had moderate OSA, and 8 patients (28.6%) had severe OSA. The median OAHI of all patients was 3.1 events/h (IQR 1.2–11.8 events/h). No patients were found to have central sleep apnea on the level I study. Only one patient was found to have hypoventilation, with a transcutaneous CO2 reading > 50 mmHg for 48.4% of the TST. For reference, Figure 1 outlines the clinical outcomes of the study participants following the level I PSG.

Clinical outcomes of the study participants following level I polysomnography.

CPAP = continuous positive airway pressure, ENT = ear, nose, and throat, OSA = obstructive sleep apnea, PAP = positive airway pressure, PSG = polysomnography.

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Figure 1

Clinical outcomes of the study participants following level I polysomnography.

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Level III Ambulatory Study Results

Ten of 28 study participants (35.7%) had moderate to severe OSA on the ambulatory level III study (AHI > 5 events/h). The severity breakdown of the OSA was as follows: mild OSA in 7 participants (25.0%), moderate OSA in 3 participants (10.7%), and severe OSA in 7 participants (25.0%). No patients were found to have central sleep apnea on the level III study. The one patient identified on the level I PSG with hypoventilation was not picked up by the level III study due to missing etCO2 data throughout the night. A total of 14 of 28 study participants (50.0%) were missing data, or had incomplete or falsely low etCO2 recordings on the level III study. Six patients had no etCO2 data because at the time of the level III study setup, the device was not initialized correctly and as a result, the etCO2 data was not recorded by the device. Four patients had falsely low etCO2 data, likely as a result of mouth breathing. Two patients each had isolated etCO2 signal loss for 45 minutes during which the airflow signal was preserved. Two patients had airflow and etCO2 signal loss for 1 hour 20 minutes and 2 hours, respectively. Results of the level I and III studies are summarized in Table 2.

Level I polysomnography and ambulatory level III study results for the study participants.

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Table 2

Level I polysomnography and ambulatory level III study results for the study participants.

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Level III Versus Level I Sleep Study Results

Using an AHI cutoff of > 1 event/h, the level III study had a sensitivity of 68.2% and specificity of 67.0% to detect SDB diagnosed by the level I PSG (Table 3). The positive predictive value of the level III study was 88.0% and the negative predictive value was 36.0%. Using this cutoff, 15 of 22 patients (68.2%) were correctly identified as having OSA and 4 of 6 patients (67.0%) were correctly identified as not having OSA on the level III study. Of the 7 patients who were not detected as having OSA on the level III study, 4 of these patients had mild OSA (OAHI 1.2, 3.1, 1.7, and 1.2 events/h), 2 of these patients had moderate OSA (OAHI 5.8 and 9.1 events/h), and 1 of these patients had severe OSA (OAHI 19.3 events/h) on the level I PSG. Two patients had a false-positive finding of OSA on the level III study. Both patients had a normal level I study (OAHI 1.0 and 0.7 events/h), but were categorized as having mild OSA on the level III study (OAHI 1.1 and 3.4 events/h, respectively).

Sensitivity and specificity of ambulatory level III versus level I polysomnography studies.

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Table 3

Sensitivity and specificity of ambulatory level III versus level I polysomnography studies.

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Using a higher AHI cutoff of ≥ 5 events/h, the level III study had a sensitivity of 61.5% and specificity was 86.7% to detect moderate to severe SDB diagnosed by the level I study. The positive predictive value of the level III study was 80.0%, and the negative predictive value was 72.0%. Using this AHI cutoff, 8 of 13 patients (61.5%) were correctly identified as having moderate to severe OSA and 13 of 15 patients (86.7) were correctly identified as not having moderate to severe OSA on the level III study. Of the 5 patients who were not detected as having moderate to severe OSA on the level III study, 3 of these patients had moderate OSA (OAHI 9.1, 9.3, and 5.8 events/h), and 2 of these patients had severe OSA on the level I PSG (OAHI 11.3 and 19.3 events/h). Two patients had falsely elevated findings of SDB on the level III study. Both patients had mild OSA on the level I PSG (OAHI 2.8 and 3.1 events/h), but had moderate and severe OSA, respectively, on the level III study (OAHI 9.8 and 14.2 events/h).

For the 28 study participants, the correlation between the OAHI and the CAHI on the level I and level III studies, respectively, were compared using Spearman correlation coefficients (Table 2). There was no significant difference between the OAHI obtained by the level III and the level I studies (Spearman correlation coefficient r = .33; P = .25). There was also no significant difference in the CAHI (Spearman correlation coefficient r = .22; P = .21).

Correlation of Carbon Dioxide Results

An analysis was performed to evaluate the correlation between the mean etCO2 and the mean tcCO2 from the level I PSG (Table 4). These values were found to be significantly correlated (P = .0097). The correlation between mean etCO2 from the level III device and mean etCO2 from the level I PSG was not found to be significantly correlated (P = .42) (Table 5). Both of the correlational analyses were performed using Pearson test, as the results were normally distributed.

Correlation of mean etCO2 compared to mean tcCO2 on the level I polysomnography studies.

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Table 4

Correlation of mean etCO2 compared to mean tcCO2 on the level I polysomnography studies.

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Correlation of mean etCO2 on the ambulatory level III studies compared to the mean etCO2 on the level I polysomnography studies.

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Table 5

Correlation of mean etCO2 on the ambulatory level III studies compared to the mean etCO2 on the level I polysomnography studies.

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Ambulatory Sleep Device Usability Questionnaire Results

A parent from each of the study participants reported on the usability of the ambulatory level III device the morning after the study. All but one parent, 27/28 (96%) would recommend using the device to another parent. Using a Likert scale of 1 to 10, with 1 defined as not willing to use the device again, the median (IQR) was 8.5 (6, 10). On a Likert scale of 1 to 10, with 1 defined as very easy and 10 defined as very difficult, the median (IQR) for the operability of the level III device was 2.4 (2, 4.7). The median (IQR) for the wearability of the device was 3 (2, 5). All 28 patients reported they would be willing to have their child wear the ambulatory level III device again if it became commercially available.

Pulmonary Function Test Results

Of the 28 patients included in our study cohort, 20 were able to complete spirometry. The mean (standard deviation [SD]) forced vital capacity (FVC) % predicted was 68.4 (16.7). The mean (SD) forced expiratory volume in 1 second (FEV1) % predicted 71.3 (17.7). Of the 13 patients with moderate to severe SDB found on level I PSG, 10 of these patients were able to complete spirometry. Only 3 of these patients (30%) had an FVC value < 60% predicted.

DISCUSSION

To our knowledge, we are reporting for the first time the diagnostic accuracy of an ambulatory level III device, with capnography using etCO2, in children with NMD at risk of SDB. Unfortunately, the sensitivity of the level III study to detect SDB was disappointingly low at 68.2% and 61.5% at AHI cutoffs of > 1 event/h and ≥ 5 events/h, respectively. As a result of the suboptimal sensitivity of the level III device, there were children with moderate and severe OSA and one child with hypoventilation identified by level I PSG that were not identified by the level III studies. Therefore, although, the numbers in our study are small, our results suggest that a level III device with capnography is not yet able to be implemented in clinical practice as a diagnostic tool for SDB in pediatric NMD. Furthermore, in our study, we demonstrated limited diagnostic accuracy of a level III sleep device in a cohort of children with NMD that recorded data from seven channels. Presumably, the diagnostic accuracy of a level III sleep device would be even lower with fewer channels.

To date, nine publications including a total of 218 children have reported on the accuracy of a level III study either in the ambulatory or in-laboratory setting as compared to the current gold standard, a technician-attended level I study.2734 Six of the nine studies are in children referred specifically for OSA. The reported sensitivity of an AHI > 5 events/h ranged between 75% to 100%.2731 Most of these children were otherwise healthy, with the exception of one study that exclusively studied obese children and another that studied children with DMD.27,28 Four studies (n = 137) performed ambulatory level III studies with sensitivities of 75%, 88%, 90%, and 100%.27,29,31,34 These studies had small numbers and a minority of children had an AHI > 5 events/h. Several other studies have evaluated the feasibility of ambulatory monitoring in both healthy patients and patients suspected of having OSA, but findings were not compared to a level I PSG study.3537

Kirk et al. have performed the only other study of level III studies in children with NMD.27 This was a pilot study in which two different level III devices were tested in 11 children with DMD.27 Only 3 of 11 children had significant SDB and 2 of 11 children were identified by both of the level III devices. However, carbon dioxide levels were not measured with either of these devices. Given the significant risk of hypoventilation as a result of disease progression in NMD, we chose to evaluate the diagnostic accuracy of a level III device with capnography. In our study, a dual-purpose nasal cannulae was used that measures both nasal airflow as well as etCO2. However, there were some technical challenges associated with the measurement of etCO2. Ambulatory transcutaneous capnography in this cohort could be explored as a future direction of study to determine if this capnography modality leads to more robust results.

Notably, the most common SDB finding on the level I PSG in our cohort was OSA instead of the anticipated hypoventilation. Children with NMD are at increased risk for OSA as a result of weakness of the pharyngeal dilator muscles in the upper airway leading to increased upper airway resistance during sleep.2 This is further compounded by obesity, as a result of many patients being nonambulatory, and most patients with DMD being treated with corticosteroids. The presence of OSA often precedes the development of nocturnal hypoventilation but can occur at any lung function.2 Based on both the British Thoracic Society (BTS) and American Thoracic Society (ATS) guidelines, all children with NMD and an FVC less than 60% predicted, muscle weakness leading to loss of ambulation, or those with symptoms of SDB should have at least annual level I PSG tests.3,8 Following these guidelines, 23 of 28 patients (92%) in our study would have been recommended for a level I PSG. Although our study cohort was small, it is important to note that if we had strictly followed the BTS criteria regarding which patients to perform surveillance PSG tests for SDB, of the five children who would not have been screened, four of them had SDB including severe OSA in one child.

There is some evidence that spirometry can be used to predict SDB, primarily hypoventilation, in patients with NMD that comes from five cross-sectional studies that used different measures and cutoffs.38,3942 The sensitivity and specificity of these cutoffs to predict nocturnal hypoventilation ranged between 64% to 97%, and 50% to 89%, respectively. In our study, the single patient with hypoventilation was unable to complete pulmonary function testing. Thus, waiting to screen patients with NMD with annual PSG tests until the FVC falls to < 60% predicted may be too late for the optimal management of SDB, notably pediatric OSA. OSA related to adenotonsillar hypertrophy, obesity, or weakness of upper airway muscles can occur with any lung function. All 28 children in our study underwent PSG because they had an NMD placing them at risk for SDB. An evaluation of the sensitivity of screening recommendations for SDB in NMD is beyond the scope of our study; however, results suggest that this is an area of further study in a larger cohort to ensure children with NMD and OSA, but not hypoventilation, are not going undiagnosed.

There are some notable limitations in our study. First, the ambulatory level III device does not have electroencephalogram recordings, which led to an inability to score arousals and subsequently may have underestimated both obstructive and central hypopneas, which are frequent in the NMD population. Second, in the ambulatory level III studies the total recording time was used as the denominator when calculating the AHI, as compared to the use of the TST that can be derived from the level I PSG.43 This could also lead to an underestimation of the AHI from the level III studies. Third, as mentioned previously, 50% of our cohort had either missing, incomplete, or poor-quality etCO2 data. For those who did have adequate etCO2 data from the level III device, correlational analysis showed that mean etCO2 did not significantly correlate with mean etCO2 obtained from the level I PSG. Therefore, a future direction for study needs to be ambulatory level III studies with tcCO2 evaluation. Additionally, parents were asked to complete the Usability Questionnaire without knowledge of the study results. Although the responses were overall favorable, it is possible that the results would have been different if the parent was aware of the quality limitations of the level III sleep study we demonstrated in our study.

CONCLUSIONS

A level III device with end-tidal capnography is not yet able to be implemented in clinical practice as a diagnostic tool for NMD in pediatric patients with NMD. As a future direction of study, ambulatory transcutaneous capnography should be evaluated given the potential of increased patient tolerability and subsequent improved ambulatory montage recordings overnight in the home in children with NMD.

DISCLOSURE STATEMENT

All authors have seen and approved the manuscript. The authors report no conflicts of interest.

ABBREVIATIONS

AHI

apnea-hypopnea index

BMI

body mass index

CAHI

central apnea-hypopnea index

DMD

Duchenne muscular dystrophy

etCO2

end-tidal carbon dioxide

FEV1

forced expiratory volume in 1 second

FVC

forced vital capacity

IQR

interquartile range

NiPPV

noninvasive positive pressure ventilation

NMD

neuromuscular disease

OAHI

obstructive apnea-hypopnea index

OSA

obstructive sleep apnea

PSG

polysomnography

SD

standard deviation

SDB

sleep-disordered breathing

tcCO2

transcutaneous carbon dioxide

TST

total sleep time

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