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Editorial Sleep-related Breathing Disorders Sleep in Children with Chronic Lung Disease Refika Ersu Marmara University, Istanbul, Turkey S leep is a vulnerable period for the respiratory system. Patients with chronic lung disease (CLD) may be at risk for hypoxemia during sleep; they have reduced baseline arterial oxygen pressure that develops with advancing lung disease. Nocturnal hypercapnia may be present in CLD without nocturnal hypoxemia or daytime gas-exchange abnormalities. Increased upper airway resistance, including nasal obstruction, is a risk factor for obstructive sleep apnoea in children with cystic fibrosis and primary ciliary dyskinesia. Sleep problems are usually underestimated in these patients. Non-invasive ventilation and supplemental oxygen may be helpful in mitigating the adverse effects of nocturnal hypercapnia and hypoxemia. Sleep should be evaluated in children with CLD to improve the care of these patients. Keywords Childhood, chronic lung disease, sleep-disordered breathing Disclosure: Refika Ersu has no conflicts of interest to declare in relation to this article. This article is a short opinion piece and has not been submitted to external peer reviewers. No funding was received in the publication of this article. Authorship: All named authors meet the International Committee of Medical Journal Editors (ICMJE) criteria for authorship of this manuscript, take responsibility for the integrity of the work as a whole, and have given final approval for the version to be published. Open Access: This article is published under the Creative Commons Attribution Noncommercial License, which permits any non-commercial use, distribution, adaptation and reproduction provided the original author(s) and source are given appropriate credit. Received: 21 February 2017 Published Online: 24 July 2017 Citation: EU Respiratory & Pulmonary Diseases, 2017;3(1):21–2 Corresponding Author: Refika Ersu, Marmara University, Division of Pediatric Pulmonology, Fevzi Çakmak Mah., Mimar Sinan Cd., No: 41 Üst Kaynarca, Pendik, Istanbul, Turkey. E: rersu@yahoo.com As physicians, we evaluate patients while they are awake in our clinic. However, sleep is a vulnerable period for the respiratory system because of reductions in minute ventilation, lower lung volumes, increased upper airway resistance and positional ventilation–perfusion mismatching. 1,2 Patients with chronic lung disease (CLD) may be at risk for hypoxemia during sleep; they have reduced baseline arterial oxygen pressure that develops over time with advancing lung disease. Also, ventilation–perfusion mismatching puts them closer to the steep-decline portion of the oxygen dissociation curve, so even the expected reduction in minute ventilation during sleep poses a risk for marked reductions in SpO2. Over time, progression of lung disease increases airway resistance and eventually results in alveolar hypoventilation. Sleep is normally characterised by hypoventilation related to decreased drive to the upper and lower respiratory muscles. Nocturnal hypercapnia may be present in CLD without nocturnal hypoxemia or daytime gas-exchange abnormalities. 3–6 Increased upper airway resistance, including nasal obstruction, is a risk factor for obstructive sleep apnoea (OSA). Cystic fibrosis (CF) and primary ciliary dyskinesia (PCD) are associated with a high incidence of chronic sino-nasal disease, including nasal polyps. OSA is associated with considerable metabolic, cardiovascular and neurocognitive morbidity. Presence of OSA may put children with CLD at increased risk for growth failure and pulmonary hypertension. Patients with chronic lung disease experience both subjective and objective sleep disruption and gas- exchange abnormalities during sleep, and sleep problems are usually underestimated in these patients. Non-invasive ventilation and supplemental oxygen may be helpful in mitigating the adverse effects of nocturnal hypercapnia and hypoxemia. 6,7 More than 50% of CF patients have disturbed sleep, especially with advanced lung disease. They also have sleep complaints such as sleep-onset insomnia, frequent awakenings, night coughing, snoring and excessive daytime sleepiness. 6 Even when stable, patients with CF report more frequent awakenings with coughing. When evaluated with objective methods, infants with CF have a sleep architecture similar to healthy controls. 8 However, children with CF have lower sleep efficiency, reduced rapid eye movement (REM) sleep and increased electrocortical arousals. Children with more severe pulmonary disease (lower forced expiratory volume in 1 second [FEV1]) have lower sleep efficiency and more nocturnal coughing. There is an association between decreased sleep efficiency and decreased mood profile, including happiness. 6 Nocturnal hypoxemia in children with CF usually precedes diurnal hypoxemia and is generally unrecognised symptomatically. Significant hypoxemia is observed primarily during REM sleep and has been associated with pulmonary hypertension. Nocturnal hypoxemia is generally present when FEV1 is <64% or if the baseline SpO2 is <93–94%. 6 In a study evaluating nocturnal hypoxia, 96% of children with CF, with normal pulmonary function tests or mild to moderate lung disease, had desaturation during sleep. Nocturnal oxygenation correlated with clinical and radiological scores, daytime PaO2 and SaO2, and Z-score of weight and height. 9 TOU CH MED ICA L MEDIA 21