The technology behind home sleep apnea tests (HSATs) has evolved over the years and made it easier to diagnose certain sleep disorders in a timely and cost effective manner using the “care closer to home” model. The American Academy of Sleep Medicine (AASM) clinical practice guidelines have approved the use of an HSAT for the diagnosis of obstructive sleep apnea (OSA), in conjunction with a comprehensive sleep evaluation, among uncomplicated adults with a high likelihood of moderate to severe OSA. However, the guidelines recommend the use of in-laboratory polysomnography (PSG) for adult patients with potential respiratory muscle weakness due to a neuromuscular condition, awake hypoventilation, or suspicion of sleep related hypoventilation because one of the major limitations of HSATs is the lack of concurrent carbon dioxide (CO2) monitoring.1 After an extensive review of the literature, the current AASM guidelines do not support the use of an HSAT for the diagnosis of OSA among healthy children due to insufficient evidence regarding technical feasibility and validity of an HSAT in children, as well as the inability to monitor CO2 or identify arousals which are both critical elements of pediatric OSA.2
There have been conflicting studies about the technical feasibility of HSAT testing among children. Goodwin and colleagues used electroencephalogram monitoring with HSATs among children 5–12 years of age and technically acceptable airflow was found in only slightly more than half the studies.3 Brockman et al. demonstrated technically acceptable recordings among 93% of patients—from newborns to 15 years of age—when the sensors were placed by a nurse.4 Conversely, Poels et al. demonstrated that only 29% of the studies were technically acceptable among children 2–7 years of age when the leads were placed by caregivers.5 In regard to validity, Tan and colleagues noted that apnea-hypopnea index (AHI) was underestimated when PSG data was converted to HSAT data by deletion of electroencephalogram, electrocardiogram and electromyogram channels which could have significantly affected clinical management decisions especially among those with moderate OSA.6 A study published in 2018 by Choi and colleagues, using the Watch-PAT 200 (WP200; Itamar Medical Ltd., Caesarea, Israel) among adolescents with concerns for OSA, demonstrated concordance in the AHI and oxygen saturation between in-laboratory PSG and Watch-PAT 200; however, the study was done simultaneously in a sleep laboratory and CO2 monitoring was not performed. The specificity of events with mild OSA was lower.7
In this issue of the Journal of Clinical Sleep Medicine, Fishman and colleagues performed a meticulous and well thought out prospective study comparing in-laboratory attended PSG versus level III HSAT studies (including CO2 monitoring) among 28 children, 6–18 years of age, with a diagnosis of neuromuscular disorder, Duchenne muscular dystrophy (DMD) being the most common diagnosis.8 Patients had a mild to borderline restrictive lung disease with a forced vital capacity (FVC) of 68.4% predicted and forced expiratory volume-one second (FEV1) of 71.3% predicted. The respiratory events were scored per the current AASM definition of hypopneas, obstructive apneas and central apneas for children. Hypoventilation was scored when > 25% of total sleep time was spent with CO2 values > 50 mmHg, measured by end tidal (etCO2) monitoring. Based on PSG findings, 46% of patients had moderate to severe sleep-disordered breathing including, mild OSA 32% of patients, moderate OSA in 17.6% of patients and severe OSA in 28.6% of patients: only one patient had hypoventilation. In contrast, HSAT demonstrated only 36% of patients with moderate to severe sleep-disordered breathing, including 25% of patients with mild OSA, 10.7% with moderate OSA, and 25% with severe OSA. Hypoventilation was not detected with the use of HSAT. Of greater concern is that 50% of study participants had incomplete or falsely low etCO2 values on the HSAT study due to either data not being recorded, mouth breathing, or signal loss.
Using an AHI cutoff of > 1 event/h, the study demonstrated low sensitivity and specificity of 68.2% and 67%, respectively with a somewhat better positive predictive value of 88% and low negative predictive value of 36%. When using this data, seven patients who were not diagnosed with OSA by HSAT were noted to have mild to severe OSA using PSG. This is concerning in a population where there is a high likelihood of OSA and symptoms may not accurately predict disease severity. Furthermore, this study population had lung function that did not place them at a high risk for sleep related hypoventilation which is more likely with a FVC < 50% predicted.9 The current recommendations among patients with DMD is the initiation of noninvasive positive pressure ventilation (NIPPV) when the FVC is < 50% of predicted or sleep related hypoventilation is noted on overnight PSG.10 Among children with spinal muscular atrophy (SMA) NIPPV should be initiated when sleep-disordered breathing is first noted during rapid eye movement sleep or FVC is < 40% predicted.11 Previous studies have noted that initiation of NIPPV for the treatment of hypoventilation can result in the improvement in gas exchange as well as slowing of lung function decay with ensuing prolongation of life.12,13
The authors acknowledge the limitations of their study, several of which are inherent to HSATs for both child and adult patients, namely the lack of electroencephalogram monitoring which can lead to the underestimation of AHI. As noted above, CO2 monitoring is also important in pediatric studies, and especially in patients with neuromuscular disorders where hypoventilation is a more likely sleep disorder. Even with CO2 monitoring added to the HSAT montage, the Fishman study suggests that this patient population would be least served by the use of HSAT given the poor correlation between etCO2 values obtained during in-laboratory testing versus home testing.
The number of patients with neuromuscular conditions may be relatively small, but emerging therapies are already altering the expected clinical course for children with SMA or DMD. Pediatric pulmonologists and sleep specialists will increasingly rely on PSG with CO2 data to help guide clinical care. Infants with SMA type I and adolescents and young adults with DMD are now being routinely managed with NIPPV rather than mechanical ventilation via tracheostomy. As physicians, we rely on accuracy of data from overnight PSG, and in diagnosing and treating these patients, the reliability of the signals from PSG are of the utmost importance. The findings from the study by Fishman and colleagues reinforce the point that HSAT is not ready for use among children with chronic medical conditions such as neuromuscular disorders given that CO2 monitoring is not available on commercial devices and the signal quality was not reliable even when CO2 monitoring was available in the research setting. “Best and safest care” with an in-laboratory PSG should still be the standard of care for these children rather than “care closer to home” with HSAT devices.
All authors have seen and approved the manuscript. Dr. Hassan has been a consultant for Biogen but there is no conflict related to this manuscript. Dr. D'Andrea reports no conflicts of interest.
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