Scoring a patient’s Apnea Hypopnea Index (AHI) has been calculated using various methods over time. Currently, as many as three hypopneas definitions are used:
Explore this issue:February 2013
- AHI Recommended: Abnormal respiratory event lasting >10 seconds, with >30 percent reduction in chest movements, plus oxygen desaturation of >4 percent.
- AHI Alternative: A reduction of nasal airflow of >50 percent, plus oxygen desaturation of >3 percent or an arousal.
- AHI Chicago: >50 percent decrease in airflow, or <50 percent decrease in airflow accompanied by oxygen desaturation >3 percent or an arousal.
Incomplete scoring definitions have a particularly negative impact for a complicated disorder when diagnosis or treatment success is based on one number: AHI. Different sleep labs use different diagnostic criteria, so scores vary from one setting to another. The Chicago version, which was used prior to 2007, tends to increase the number of hypopneas, while the recommended scale, implemented by the American Academy of Sleep Medicine (AASM) in 2007, decreases them.
The current recommended definition focuses only on desaturations, with no importance given to arousals from sleep. Pell Ann Wardrop, MD, medical director of the St. Joseph Sleep Wellness Center in Lexington, Ky., explained that this omission causes problems for women and some younger men during the initial diagnosis process. These patients often experience more arousals, with fewer instances of oxygen desaturation. When arousals re not scored, these individuals are found not to have sleep apnea and receive no therapy—and no relief.