From the Guidelines
The Apnea-Hypopnea Index (AHI) is used to classify the severity of sleep apnea based on the number of breathing disruptions per hour of sleep, with an AHI less than 5 considered normal, 5-15 indicating mild sleep apnea, 15-30 indicating moderate sleep apnea, and above 30 indicating severe sleep apnea, as stated in the most recent guideline 1. The AHI classification is crucial in determining the appropriate treatment approach for sleep apnea, with higher AHI values typically requiring more aggressive interventions.
- Mild sleep apnea (AHI 5-15) may be managed with lifestyle modifications such as weight loss or positional therapy.
- Moderate to severe sleep apnea (AHI 15-30 or above 30) often requires continuous positive airway pressure (CPAP) therapy, oral appliances, or in some cases, surgical interventions. The AHI should be interpreted in conjunction with other clinical factors, including symptoms such as daytime sleepiness, morning headaches, and concentration difficulties, as well as oxygen desaturation levels and comorbidities, to provide a comprehensive understanding of the condition's impact and guide treatment decisions, as supported by recent studies 1. It is essential to note that sleep apnea is associated with an increased risk of mortality, stroke, and other cardiovascular risk factors, emphasizing the importance of accurate diagnosis and effective treatment, as highlighted in recent guidelines 1.
From the Research
Interpretation of Apnea-Hypopnea Index (AHI) Percentage
The Apnea-Hypopnea Index (AHI) is a measure used to assess the severity of sleep apnea, with higher values indicating more severe sleep apnea. The interpretation of AHI percentage can be understood through the following points:
- AHI is calculated as the number of apnea and hypopnea events per hour of sleep, with values ranging from normal (less than 5) to severe (30 or more) 2, 3, 4, 5, 6.
- Treatment of sleep apnea is considered successful when the AHI is reduced to less than 5 or shows a substantial reduction of at least 50% from the baseline value to a value of less than 20 in a patient without sleep apnea symptoms while undergoing therapy 2.
- The AHI can be influenced by various factors, including the duration and severity of apnea and hypopnea events, with some studies suggesting that novel indices such as total duration of sleep apnea and hypopnea events (TAHD%) and a combined index including duration and severity of the events (TAHD% × average desaturation) may provide supplementary information to AHI when diagnosing the severity of sleep apnea 3.
- The effectiveness of continuous positive airway pressure (CPAP) therapy in reducing AHI depends on regular use, with studies showing that even in ideal patients, CPAP cannot eliminate respiratory events due to limited adherence 4.
- The correlation between AHI determined by manual scoring and by auto-CPAP devices has been evaluated, with strong correlations observed between the overall AHI and the AHI determined by auto-CPAP devices, although weaker correlations were found when analyzing the hypopnea component separately 5.
- The mean apnea-hypopnea duration (MAD) has been compared to AHI as indicators of clinical and demographic parameters, blood oxygenation, and sleep parameters in patients with sleep apnea, with results showing that MAD was significantly correlated with AHI, but showed no significant associations with patient age, body weight, and height 6.
AHI Classification
The AHI can be classified into different categories, including:
- Normal: less than 5 events per hour
- Mild: 5-14 events per hour
- Moderate: 15-29 events per hour
- Severe: 30 or more events per hour These categories are used to determine the severity of sleep apnea and guide treatment decisions 2, 3, 4, 5, 6.
Limitations of AHI
While AHI is a widely used measure of sleep apnea severity, it has some limitations, including:
- AHI may not capture the full range of sleep apnea symptoms and severity
- AHI can be influenced by various factors, including the duration and severity of apnea and hypopnea events
- AHI may not be directly comparable across different studies and populations These limitations highlight the need for additional measures and indices to provide a more comprehensive understanding of sleep apnea severity and treatment outcomes 3, 6.