What is the definition of Positional (POS) Obstructive Sleep Apnea (OSA)?

Definition of Positional Obstructive Sleep Apnea (POSA)

Positional Obstructive Sleep Apnea (POSA) is defined as a condition where the apnea-hypopnea index (AHI) in the supine position is at least twice as high as the AHI in the non-supine position, with no relevant non-supine AHI (<15 events/hour). 1, 2

Key Diagnostic Criteria

• Supine AHI at least twice as high as non-supine AHI 1, 2
• Non-supine AHI should be less than 15 events/hour to be considered clinically significant positional OSA 1
• Minimum time spent in both supine and non-supine positions during sleep study (typically 30 minutes to 1 hour of sleep in each position) 1

Subtypes of Positional OSA

Two main subtypes have been identified:

1. Supine-predominant OSA (spOSA):

   • Meets the basic POSA criteria (supine AHI > 2× non-supine AHI)
   • Still has clinically significant non-supine AHI (≥5 events/hour) 3

2. Supine-isolated OSA (siOSA):

   • Meets the basic POSA criteria
   • Non-supine AHI is negligible (<5 events/hour) 3
   • Represents approximately 27% of POSA cases 3

Epidemiology and Clinical Significance

• Approximately 50% of all OSA patients have positional OSA 2, 4
• POSA patients tend to have:
  • Lower overall AHI compared to non-positional OSA patients 2
  • Lower BMI than non-positional OSA patients 2
  • Younger age than non-positional OSA patients 2

Clinical Implications

• Positional therapy can be considered for mild to moderate positional OSA 1, 2
• The European Respiratory Society suggests either vibratory positional therapy or CPAP for patients with mild or moderate position-dependent OSA 1
• For accurate diagnosis, sleep position should be properly documented during polysomnography 2, 5
• About one-third of positional OSA patients may change to non-positional OSA over time, particularly those with a higher apnea index in the lateral position 6

Treatment Considerations

• Vibratory positional devices show better adherence than traditional methods like tennis ball technique 1, 2
• CPAP remains more effective at reducing AHI but has lower compliance compared to positional therapy 1, 2
• Positional therapy has fewer side effects compared to CPAP 1
• Follow-up sleep studies are recommended to confirm the effectiveness of positional therapy 2

Understanding this definition and its clinical implications is crucial for appropriate diagnosis and management of patients with this specific subtype of obstructive sleep apnea.