What determines moderate to severe Obstructive Sleep Apnea (OSA)?

From the Guidelines

Moderate to severe obstructive sleep apnea is determined primarily through the Apnea-Hypopnea Index (AHI), which measures the number of breathing interruptions per hour during sleep, with an AHI of 15-30 events per hour indicating moderate sleep apnea and an AHI greater than 30 events per hour indicating severe sleep apnea, as recommended by the 2024 European Heart Journal guidelines 1. The diagnosis of moderate to severe obstructive sleep apnea (OSA) is crucial for guiding treatment decisions and improving patient outcomes. The AHI is typically obtained through a sleep study, such as polysomnography, which monitors various physiological parameters during sleep.

Key Considerations

• The sleep study can be conducted in a sleep laboratory or at home using portable monitoring devices, though laboratory testing is considered more comprehensive 1.
• In addition to the AHI, doctors may consider oxygen desaturation levels, with significant drops below 90% suggesting more severe disease.
• Symptom severity is also taken into account, including the degree of daytime sleepiness, cognitive impairment, and presence of comorbidities like hypertension or heart disease.

Treatment Implications

• The distinction between moderate and severe OSA is important as it guides treatment decisions, with CPAP therapy being the primary treatment for moderate to severe cases, while mild cases might be managed with lifestyle modifications or oral appliances 1.
• CPAP therapy is indicated for moderate (AHI of 15–30) and severe (AHI > 30) OSAS, and usually improves BP control and helps to resolve resistant hypertension 1.

From the Research

Determining Moderate to Severe Obstructive Sleep Apnea

• Moderate to severe obstructive sleep apnea can be determined through various methods, including polysomnography and home sleep apnea testing 2, 3.
• The apnea-hypopnea index (AHI) is regularly used to define OSA severity, with higher values indicating more severe OSA 2, 3.
• However, recognition is increasing of the inability of AHI to risk-stratify patients, and other sleep study data such as arousal threshold, hypoxic burden, and pulse rate variability, as well as clinical characteristics, can help with risk stratification 2.
• Acoustic pharyngometry measurement of minimal cross-sectional airway area is also a significant independent predictor of moderate-to-severe obstructive sleep apnea 4.
• Polysomnography is the laboratory procedure to study sleep and its protean dysfunctions, and includes multiple physiologic parameters such as electroencephalogram (EEG), electrooculogram (EOG), electromyogram (EMG), electrocardiogram (ECG), respiratory effort, air flow, and oxygen saturation 5.

Diagnostic Tools

• Home sleep apnea testing has a sensitivity of approximately 80% and can be used to diagnose OSA in many patients 3.
• In-laboratory polysomnography is the most commonly used diagnostic tool in the identification and monitoring of OSA, but new methods for diagnosis and at-home monitoring of treatment response are being developed and validated 2.
• Split-night studies can also be used to diagnose OSA, and involve a combination of polysomnography and CPAP titration 5.

Severity Classification

• OSA can be classified as mild, moderate, or severe based on the AHI value, with mild OSA defined as an AHI of less than 15, moderate OSA defined as an AHI of 15-30, and severe OSA defined as an AHI of greater than 30 2, 3.
• The Epworth Sleepiness Scale (ESS) can also be used to assess the severity of OSA, with higher scores indicating greater daytime sleepiness 6, 4.