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Sleep Apnea: Classification

Sleep apnea is broken down into obstructive apnea syndromes, central apnea syndromes (e.g. primary, Cheyne-stokes, altitude, iatrogenic) and hypoventilation/hypoxemia syndromes (e.g. congenital, secondary to lung disease, neuromuscular related) and undefined. Obstructive apnea is characterized by periodic narrowing and complete obstruction of the pharynx with recorded effort whereas Central apnea is characterized by an absence of respiratory effort.

The Apnea Hypopnea Index (AHI) stratifies the severity of sleep apnea. Apneas are >90% reduction in airflow for at least 10sec whereas hypopneas are partial obstructions of at least 10sec where thoracoabdominal movement is reduced by 50% or a 30% reduction in airflow measured by nasal pressure transducer.

Polysomnography is the gold standard for measurement of AHIs and diagnosis of sleep apnea. Severity of sleep apnea is classified accordingly:

None/Minimal: AHI < 5 per hour

Mild: AHI ≥ 5, but < 15 per hour

Moderate: AHI ≥ 15, but < 30 per hour

Severe: AHI ≥ 30 per hour

Patients w/ AHI >=5 and concomitant symptoms (daytime sleepiness, hypersomnolence, insomnia, snoring, witnessed breathing pauses, cognitive impairment, waking up gasping for air) or alternatively AHI>=15 regardless of symptoms are positive for a diagnosis of sleep apnea.


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