Sleep-disordered breathing: Screening tools and definition of key terms
Presently, there are no screening guidelines for sleep-disordered breathing in pediatric or adult CF patients. Screening questionnaires and tools exist for obstructive sleep apnea (OSA) in the non-CF population, but there are no tools for screening for the rest of the spectrum of sleep-disordered breathing. Objective tests exist to diagnose nocturnal hypoxia , apneas, and nocturnal hypoventilation.
Nocturnal hypoxemia is defined as oxygen saturation ≤90% in children and ≤88% in adults for >5 minutes. As per the AASM definition, hypoventilation during sleep in children is defined as arterial PCO2 (or surrogate) being greater than 50 mm Hg for more than 25% of total sleep time. For adults, sleep hypoventilation is scored when the arterial PCO2 (or surrogate) is > 55 mm Hg for ≥ 10 minutes or there is an increase in the arterial PCO2 (or surrogate) ≥ 10 mm Hg (in comparison to an awake supine value) to a value exceeding 50 mm Hg for ≥ 10 minutes.8
Of all the sleep disordered breathing disorders, OSA has the most abundant tools and screening questionnaires, both for pediatric and adult populations. In the pediatric population, modified questionnaires and/or the presence of snoring are used for further evaluation of OSA.28 It has been recommended by the American Academy of Pediatrics that enquiring about snoring at each clinical visit may be a sensitive screening measure for OSA that is quick and easy to perform.28 In adults, multiple different tools are available for OSA screening, such as STOP-BANG, Berlin Criteria, and the Epworth Sleepiness Scale (ESS).29
In the pediatric population, obstructive apnea has been defined as a decrease in nasal pressure or oronasal thermal airflow ≥ 90% of pre-event baseline for ≥ 2 breaths with presence of respiratory effort.30 Hypopneas in the pediatric population are identified by a decrease in nasal pressure or oronasal thermal airflow ≥ 30% of pre-event baseline for ≥ 2 breaths with ≥ 3% oxygen desaturation from pre-event baseline or an associated arousal. The diagnostic criteria for OSA in children is the presence of ≥ 1 obstructive apnea or hypopnea per hour of sleep (apnea-hypopnea index (AHI) ≥ 1 per hour).8
In adults, obstructive apnea has been defined as a decrease in nasal pressure or oronasal thermal airflow ≥ 90% of pre-event baseline for ≥ 10 seconds with continued or increased inspiratory effort.30 Hypopneas are defined as decrease in nasal pressure or oronasal thermal airflow ≥ 30% of pre-event baseline for ≥ 10 seconds with ≥ 3% oxygen desaturation from pre-event baseline.30 The diagnostic criteria for OSA in adults is the presence of ≥ 5 obstructive apneas or hypopneas per hour of sleep or per hour of monitoring (AHI ≥ 5 per hour).8
Hypoventilation in sleep, defined by a decrease in minute ventilation, is normal in healthy controls and is more pronounced in those with lung disease. In rapid eye movement (REM) sleep, respiratory muscle function is reduced, during which diaphragm contraction is preserved, and minute ventilation can decrease more than 15% in this phase of sleep in normal individuals31. This decrease of respiratory muscle function in patients with lung disease is more pronounced7 , and furthermore, patients with hyperinflation have decreased diaphragm contraction4,32. A decrease in minute ventilation while asleep can lead to hypercapnia.