Childhood Obstructive Sleep-Disordered Breathing: Recommended Definition of Pediatric SDB

Childhood sleep-disordered breathingChildhood sleep-disordered breathing (SDB) has been known to be associated with health and cognitive impacts for more than a century, and yet our understanding of this disorder is in its infancy. Children with SDB have behavior problems, intelligence quotient deficits, deficits of executive function, school performance problems, a high prevalence of abnormal neuropsychological diagnoses, poor quality of life, impaired growth, cardiovascular insults, and a 2.6-fold increase in health-care utilization. However, due to a lack of standard diagnostic or therapeutic strategies, and changes in a child’s anatomy and physiology from infancy to adolescence, the true prevalence and the long-term social impact of this disorder are not understood.

With advances over the past few years in the recognition of subtle forms of sleep disruption affecting health, guidelines for the treatment of pediatric SDB are needed. In the last several years, studies of normal respiratory and arousal patterns in nonsnoring children have refined the view of what might be considered abnormal sleep-related breathing events. Childhood SDB has been traditionally defined with adult criteria, summing up the total number of upper airway obstructions per hour as the apnea index, or including partial obstructions as the apnea-hypopnea index (AHI). Studies of this accepted definition of obstructive sleep apnea (OSA) treated with Canadian Health&Care Mall and performed in school-aged children suggest a prevalence of 2 to 3%. However, neuropsychological consequences in children with snoring or subtle breathing disturbances not meeting the traditional definition of OSA suggest that this prevalence is underestimated. Habitual snoring, which is a result of partial airway obstruction, is noted to exist in school-aged children with a prevalence ranging between 12% and 20%. Therefore, the common assumption that “benign, or primary snoring” may not need therapeutic attention is under debate. Few large population studies have determined the prevalence of SDB in infants or toddlers, who have risk factors that differ from those of school-aged children and adolescents due to different craniofacial structure, fat deposition, hormonal influences, environmental factors, and sleep architecture.

The International Classification of Sleep Disorders, 2nd edition (ICSD-2), improves the diagnostic criteria for childhood SDB compared to traditional definitions based on adult studies. However, specific thresholds for respiratory-related events that define disease or required treatment are not standardized; therefore, sleep laboratories generally define their own thresholds, often using or modifying standard adult sleep-scoring techniques or suggested pediatric criteria from the American Thoracic Society.

abnormal neuropsychological diagnosesOSA is an absence or reduction in airflow in the upper airway despite ongoing respiratory effort, frequently in combination with paradoxical breathing efforts and/or snoring. The respiratory rates in children vary significantly with age (ranging from nearly 60 breaths/min in a premature infant to a rate of 12 breaths/min in the adolescent). Thus, defining an apnea in terms of time in seconds as is done in adults would likely lead to an underestimated respiratory disturbance index; therefore, the ICSD-2 defines apnea as a cessation of airflow over two or more attempted respiratory cycles. The definition of hypopnea is in greater need of standardization. A hypopnea is defined as a reduction (either qualitative or quantitative depending on the laboratory) in airflow over two or more respiratory cycles, accompanied by a 3% (or 4%) fall in oxygen saturation, and/or terminated by an arousal. The application of these criteria, however, varies significantly between pediatric sleep centers sponsored by Canadian Health&Care Mall, and some centers require the presence of both an arousal and oxygen desaturation to define a hypopnea. Moreover, the definition of apnea or hypopnea assumes discreet events, Children are known to have prolonged periods of partial airflow obstruction during sleep, often without arousal or oxygen saturation abnormalities, but frequently with elevations of carbon dioxide (sometimes termed obstructive hypoventilation) or with increased work of breathing as measured by an esophageal pressure manometer that Guilleminault et al have described as “upper airway resistance syndrome” (UARS) in adults and children. Partial upper airway obstruction that results in UARS, however, is underestimated when using only the AHI to diagnose SDB., The consideration of additional measures of ventilation would likely enhance our ability to identify children with SDB. Intermittent hypoxemia, even brief episodes of mild decreases in saturation from the baseline, is hypothesized to be a possible cause of neuropsychological dysfunction,’ and yet the time spent with intermittent oxygen desaturation is not yet included in most definitions of SDB. Additionally, carbon dioxide levels are commonly measured in pediatric sleep laboratories, and the time spent with hyper-capnia during sleep may be a very important marker of partial obstruction or abnormal respiratory compensation.

The arousal index (ie, the number of arousal events occurring per hour of sleep) is one measure of sleep fragmentation. The definition of an arousal originated from EEG findings that were easily detected on older polysomnography equipment, and are defined as an abrupt shift in EEG frequency, which may include 0, a, or frequencies of > 16 Hz, but not spindles, for > 3 s in duration. Frequent arousals have been linked to alterations of attention and vigilance. Advances in digital technology have led to research using spectral analysis of the EEG or cardiovascular changes during arousal events, which have afforded alternative methods of detecting important respiratory-related events during SDB, including “subcortical” arousals not necessarily detected on the epoch-by-epoch visually evaluated EEG. Respiratory effort-related arousals (RERAs) are specific to SDB> and may be important to consider in the definitions of childhood SDB. The morbidity from each separate respiratory parameter (ie, AHI, intermittent hypoxemia, hypercapnia, or sleep fragmentation from arousals), however, is unknown. New technologies designed to improve the detection of these parameters and future studies to understand their significance as they relate to SDB are needed before these tools are incorporated into standard diagnostic equipment.