Does a patient with an Apnea-Hypopnea Index (AHI) of 6 and a Central Apnea Index (CAI) of 2.5 meet the criteria for Obstructive Sleep Apnea (OSA)?

Diagnosis of Obstructive Sleep Apnea with AHI 6 and CAI 2.5

Yes, a patient with an Apnea-Hypopnea Index (AHI) of 6 and a Central Apnea Index (CAI) of 2.5 meets the diagnostic criteria for mild Obstructive Sleep Apnea (OSA).

Diagnostic Criteria Analysis

The American Academy of Sleep Medicine (AASM) defines OSA based on the following criteria:

• An AHI ≥5 events per hour is considered diagnostic for OSA 1
• OSA severity is categorized as:
  • Mild: AHI 5-15 events/hour
  • Moderate: AHI 15-30 events/hour
  • Severe: AHI ≥30 events/hour 1

In this case:

• Total AHI = 6 (exceeds the diagnostic threshold of 5)
• Central Apnea Index (CAI) = 2.5
• By subtraction, the Obstructive Apnea Index would be 3.5

Interpretation of Mixed Sleep Apnea Components

When evaluating a patient with both central and obstructive components:

• The presence of central apneas doesn't negate an OSA diagnosis when the total AHI exceeds 5 2
• Central sleep apnea components are often found alongside obstructive events, particularly in patients with severe sleep apnea hypopnea syndrome 3
• The AASM acknowledges common pathogenic mechanisms between obstructive and central apnea syndromes, though they are typically discussed separately 4

Clinical Implications

This patient's presentation indicates:

1. Mild OSA classification: With an AHI of 6, this falls into the mild OSA category (5-15 events/hour)

2. Mixed apnea pattern: The presence of central apneas (CAI 2.5) alongside obstructive events is not uncommon and doesn't preclude an OSA diagnosis 3

3. Treatment considerations:

   • For mild OSA, treatment options include behavioral modifications and weight loss
   • Continuous positive airway pressure (CPAP) should be considered, especially if the patient has symptoms or comorbidities
   • Oral appliances can be considered as an alternative for mild OSA 5

Important Caveats

• The diagnosis should consider both the AHI and clinical symptoms. Patients should have excessive daytime sleepiness or at least two symptoms like choking/gasping during sleep, recurrent awakenings, unrefreshing sleep, daytime fatigue, or impaired concentration 4

• The definition of hypopnea used in the sleep study can significantly impact the AHI value. The AASM acknowledges two valid definitions:

  • Recommended definition: ≥30% reduction in airflow with ≥3% oxygen desaturation
  • Alternative definition: ≥30% reduction in airflow with EITHER ≥3% oxygen desaturation OR an arousal 1, 2

• Relying solely on AHI for diagnosis and severity classification has limitations, as it may not fully capture the clinical impact of sleep-disordered breathing 6

In conclusion, this patient meets the diagnostic threshold for mild OSA based on the AHI of 6, despite having a central component (CAI 2.5). Treatment decisions should consider both the severity of OSA and the presence of symptoms or comorbidities.