Polysomnographic variables in children

	Definition	Comments
Events
Apnea	≥90% decrease in airflow signal for a duration of ≥2 breaths^*	Apnea is obstructive if there is respiratory effort throughout the entire period of absent airflow. Apnea is central if there is absent inspiratory effort throughout the entire duration of the event and at least 1 of the following is met: Event lasts ≥20 seconds Event lasts at least the duration of 2 breaths^* and is associated with an arousal or a ≥3% drop in arterial oxygen saturation Event lasts at least the duration of 2 breaths^* and is associated with a decrease in HR to <50 bpm for at least 5 seconds (or, for infants <1 year, a decrease in HR <60 bpm for 15 seconds) Apnea is mixed if it is associated with 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 for the duration of ≥2 breaths^* and a ≥3% drop in oxygen saturation, or the event is associated with an arousal.	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	A sequence of breaths lasting ≥2 breaths^* that does not meet criteria for an apnea or hypopnea and leads to an arousal from sleep. One or more of the following must also be present: Increasing respiratory effort Flattening of the airflow signal Snoring Elevation in the end-tidal PCO₂ above the pre-event baseline^¶	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. 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.

AHI: apnea-hypopnea index; bpm: beats per minute; CO₂: carbon dioxide; HR: heart rate; OSA: obstructive sleep apnea; PCO₂: partial pressure of carbon dioxide; PSG: polysomnography; RDI: respiratory disturbance index; RERA: respiratory effort-related arousal; UARS: upper airway resistance syndrome.

* As determined from the baseline breathing pattern.

¶ Arousals are determined by electroencephalographic 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 5.0

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Polysomnographic variables in children