What is the acceptable upper limit of air leak via a Continuous Positive Airway Pressure (CPAP) mask for adult patients with sleep apnea, including those with overlap syndrome and Chronic Obstructive Pulmonary Disease (COPD)?

Acceptable Upper Limit of Air Leak via CPAP Mask

The acceptable upper limit of unintentional air leak varies by manufacturer but generally should not exceed 24 L/min for nasal interfaces and 36 L/min for full-face interfaces, based on the 95th percentile thresholds established by major CPAP manufacturers. 1

Manufacturer-Specific Leak Thresholds

The American Thoracic Society guidelines provide specific large leak thresholds that differ by manufacturer:

• ResMed devices: Define excessive unintentional leak as >24 L/min with nasal interface and >36 L/min with full-face interface (95th percentile leak) 1
• Fisher & Paykel: Set the threshold for total leak (including mask and exhaust flow) at >60 L/min 1
• DeVilbiss Healthcare IntelliPAP: Record high leak flow time when leak exceeds 95 L/min 1
• Philips Respironics: Use a preset "flow vs. pressure" curve rather than a fixed threshold, as leak varies with pressure level 1

Clinical Significance of Leak

Impact on Therapy Efficacy

Excessive leak compromises CPAP effectiveness and should prompt immediate mask adjustment. 1 The clinical consequences include:

• Central apnea development: Higher maximum leak (75.0 L/min vs. 59.5 L/min) is significantly associated with emergence of central apneas during CPAP titration (p=0.003) 2
• Pressure underestimation: Air leaks cause auto-PAP devices to underestimate required pressure and overestimate delivered pressure at the upper airway 3
• Device performance degradation: Some auto-PAP devices decrease pressure response by 56% when leak increases from baseline to 30 L/min 3

Practical Leak Management Algorithm

When any significant unintentional leak is observed during titration, mask refit or readjustment should be performed immediately. 1 Follow this approach:

1. Identify leak type: Distinguish between intentional leak (controlled port on mask), mouth leak (with nasal mask), and mask leak (between mask and face) 1

2. Immediate interventions:

   • Refit or readjust mask for mask leak 1
   • Add chinstrap or switch to full-face/oronasal mask for mouth leak 1
   • Verify leak is not substantially higher than manufacturer's intentional leak vs. pressure curve 1

3. Monitor for sudden changes: A sudden increase in leak without pressure change indicates new mask or mouth leak requiring intervention 1

Evidence-Based Leak Thresholds

Research Supporting Lower Thresholds

For nasal masks specifically, average leak should ideally remain below 50 L/min to minimize risk of central apnea. In patients titrated with nasal masks, those who developed central apnea (CAI ≥5/hour) had median average leak of 50.0 L/min compared to 42.0 L/min in those without central apnea (p=0.001) 2

Device-Specific Performance Limits

Auto-PAP devices maintain appropriate function when leak remains within 20-50 L/min depending on the device. 3 Specifically:

• GoodKnight 418P performs appropriately when leak is within 20 L/min 3
• Autoset-T maintains function up to 50 L/min of leak 3

Common Pitfalls to Avoid

Do not rely on fixed leak values alone—clinical judgment based on sudden leak changes and manufacturer specifications is essential. 1 Key considerations:

• Intentional leak increases with pressure, making absolute leak values pressure-dependent 1
• Leak type varies by interface (nasal vs. full-face), requiring different thresholds 1
• Excessive leak can worsen oxygenation, increase arousal index, and decrease REM sleep 1
• Average nightly leak of 27.5-28.0 L/min appears tolerable in clinical practice without affecting compliance 4

Special Populations

For patients with overlap syndrome (OSA + COPD) or those requiring BiPAP, the same leak thresholds apply, but vigilance is heightened as leak can compromise ventilation. 5, 6, 7 In hypercapnic patients, excessive leak should be checked before further pressure adjustments if tidal volume fails to increase with pressure support 5