Polysomnographic variables in children

	Definition	Comments
Events
Apnea	>90% decrease in airflow signal that lasts ≥90% of the duration of at least 2 normal breaths, as determined from the baseline breathing pattern.	Apnea is obstructive if there is continued or increased inspiratory effort during the entire period of decreased airflow. Apnea is central if inspiratory effort is absent during the entire period of airflow cessation. Apnea is mixed* if there is absent respiratory effort during 1 portion of the event and the presence of inspiratory effort in another portion, regardless of which portion comes first.
Hypopnea	≥30% decrease in airflow signal that lasts ≥90% of the duration of at least 2 normal breaths, as determined from the baseline breathing pattern. The decreased airflow is associated with an arousal or at least 3% oxyhemoglobin desaturation.	Hypopneas may be classified as either obstructive or central, depending on the presence or absence of snoring, flattening of nasal pressure signal, or paradoxical thoracoabdominal breathing. However, in practice, accurate classification of the etiology of hypopneas is challenging and usually not performed. In a patient who has clear OSA, hypopneas are usually assumed to have an obstructive basis.
RERA	Respiratory event (increasing respiratory effort, flattening of the inspiratory portion of the nasal pressure waveform, snoring, or an elevation in the end-tidal PCO₂) that leads to arousal and does not qualify as an apnea or hypopnea^¶.	RERAs can be detected with routinely used sensors on in-laboratory PSG or by addition of esophageal manometry. UARS was previously used to describe presence of RERAs in the absence of apneas or hypopneas. UARS is now subsumed into the category of OSA.
Sleep-related hypoventilation	End-tidal or transcutaneous CO₂ >50 mmHg for more than 25% of the total sleep time.	Some children with breathing disturbance due to increased upper airway resistance have hypoventilation but not discrete apneas or hypopneas. Obstructive hypoventilation is now subsumed into the category of OSA.
Additional events	Arousals, snoring, changes in body position, and limb movements.
Summary measures
AHI	The number of apneas plus hypopneas that occur per hour of sleep.	Concern for clinically significant OSA generally starts with an AHI >1 or RDI >1. An AHI ≥1.5 events per hour was considered abnormal based on a study of a group of healthy children not suspected of having sleep-related breathing disorders, in whom the mean AHI was 0.2±0.6 events per hour^[1].
RDI	The number of apneas, hypopneas, and RERAs per hour of sleep.	Concern for clinically significant OSA generally starts with an AHI >1 or RDI >1. Some experts have advocated slightly higher RDI thresholds, such as 1.5, 2, or 3 events per hour. An RDI >5 events per hour of sleep is often used to identify an abnormal RDI in adults but is insufficiently sensitive for children.

OSA: obstructive sleep apnea; RERA: respiratory effort-related arousal; PCO₂: partial pressure of carbon dioxide; PSG: polysomnography; UARS: upper airway resistance syndrome; CO₂: carbon dioxide; AHI: apnea hypopnea index; RDI: respiratory disturbance index; EEG: electroencephalographic.

* Central apnea also requires 1 of the following measures of duration:

Respiratory event is at least 20 seconds long
Inspiratory effort is absent for the duration of 2 respiratory cycles and is followed by a cortical arousal, or oxygen desaturation ≥3%
Event is associated with a decrease in the heart rate to less than 50 beats per minute for at least 5 seconds, or less than 60 beats per minute for 15 seconds (infants under 1 year of age only)

¶ Arousals are determined by EEG criteria.

Reference:

Witmans MB, Keens TG, Davidson Ward SL, Marcus CL. Obstructive hypopneas in children and adolescents: normal values. Am J Respir Crit Care Med 2003; 168:1540.

Data from: Troester MM, Quan SF, Berry RB, et al. The AASM Manual for the Scoring of Sleep and Associated Events: Rules, Terminology and Technical Specifications, Version 3, American Academy of Sleep Medicine 2023.

Graphic 111056 Version 4.0

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Polysomnographic variables in children