Obstructive sleep apnea (OSA) is a chronic condition affecting nearly one billion people globally. It is characterized by repeated partial or complete upper airway collapses during sleep, leading to sleep disturbances, intermittent hypoxemia, and significant reductions in quality of life.

The apnea-hypopnea index (AHI) and oxygen desaturation index (ODI) are commonly used metrics for diagnosing and assessing OSA severity.These metrics have significant limitations, including weak correlations with symptoms, quality of life, and nocturnal oxygen desaturation—the primary contributor to OSA’s systemic complications.

There are limitations of the apnea-hypopnea index (AHI) and the oxygen desaturation index (ODI) as measures for diagnosing and quantifying the severity of obstructive sleep apnea (OSA).Main limitations are-

  1. Inadequate Measurement of Duration and Depth:
    • Both AHI and ODI fail to account for the duration and depth of respiratory events and their resulting oxygen desaturations.
  2. Equal Weight to Different Event Types:
    • AHI treats apneas (complete pauses in breathing) and hypopneas (partial reductions in airflow) as equivalent, which might oversimplify the severity of events. Patients with apnea-predominant OSA had more severe disease than those with hypopnea-predominant OSA. In addition, multilevel upper airway surgery may induce the transition from apnea to hypopnea in patients with apnea-predominant OSA. (https://doi.org/10.1111/coa.13998)
  3. Arbitrary Thresholds:
    • The definitions of hypopnea and the thresholds for desaturation (3% or 4%) are inconsistent across sleep labs and research studies.
    • Events shorter than 10 seconds, which can still cause significant desaturation, are excluded.
  4. Influence of Non-OSA Factors:
    • ODI and AHI may include oxygen desaturations caused by conditions unrelated to OSA, such as other cardiopulmonary diseases or obesity-related nocturnal hypoxemia.
  5. Incomplete Recovery:
    • Desaturation severity is underestimated when oxygen saturation does not fully return to baseline after an event.

These limitations highlight the need for new metrics, such as hypoxic burden (HB) and other novel metrics, to provide a more comprehensive and clinically relevant assessment of OSA.

Several new metrics have been proposed to better predict cardiovascular/metabolic and mortality outcomes in OSA. Some of them are summarised below. (https://doi.org/10.5664/jcsm.10298)

These types of metrics may thus provide the opportunity to risk-stratify patients for more aggressive therapy for OSA and other risk factors, contributing to a precision care approach. These metrics may help to select individuals who would be at increased risk of adverse outcomes (eg, cardiovascular [CV] events) who might then be preferentially recruited into randomized controlled trials.