AVAPS pMax Setting Strategy
For AVAPS (Average Volume-Assured Pressure Support) mode, set IPAPmax at 25-30 cm H₂O for adults ≥12 years and 20 cm H₂O for children <12 years, with IPAPmin at EPAP + 4 cm H₂O and EPAP starting at 4 cm H₂O. 1
Initial AVAPS Settings
The American Academy of Sleep Medicine consensus guidelines provide clear starting parameters for volume-targeted BPAP (AVAPS):
- EPAP: 4 cm H₂O (lowest available on most devices)
- IPAPmin: EPAP + 4 cm H₂O (typically 8 cm H₂O initially)
- IPAPmax: 25-30 cm H₂O for patients ≥12 years; 20 cm H₂O for patients <12 years
- Target tidal volume: ~8 mL/kg ideal body weight 1
Rationale for pMax Selection
The IPAPmax setting creates the upper boundary within which the device automatically adjusts pressure support to deliver the target tidal volume. Setting IPAPmax at 25-30 cm H₂O allows sufficient range for the device to compensate for declining respiratory muscle strength, increased airway resistance, or changing sleep stages while maintaining adequate ventilation. 1
The maximum IPAP of 30 cm H₂O represents the upper limit available on most NPPV devices and aligns with safety parameters established for adult patients. The lower 20 cm H₂O maximum for pediatric patients (<12 years) reflects reduced tolerance and different physiological requirements in this population. 1
Adjusting EPAP Within AVAPS
While IPAPmax defines the upper pressure limit, EPAP must be titrated independently to eliminate obstructive events (apneas, hypopneas, RERAs, snoring) following standard CPAP titration protocols. 1 The device then automatically varies IPAP between IPAPmin and IPAPmax to maintain target tidal volume.
Clinical Context and Mode Selection
AVAPS represents an acceptable alternative to fixed-level pressure support, particularly when:
- Respiratory muscle strength fluctuates during sleep
- Tidal volumes are inconsistent on fixed BiPAP
- Automatic adjustment is desired to maintain consistent minute ventilation 1
However, current evidence shows AVAPS achieves equivalent outcomes to properly titrated fixed-level pressure support in most conditions including obesity hypoventilation syndrome 2, acute hypercapnic respiratory failure 3, and COPD 4. The faster CO₂ correction seen with AVAPS in some acute settings 4 has not translated to improved survival or reduced intubation rates across most studies 3, 5.
Backup Rate and Inspiratory Time
When using AVAPS in spontaneous-timed (ST) or timed modes:
- Backup rate: Set at or slightly below spontaneous sleeping respiratory rate (minimum 10 bpm)
- Inspiratory time: 30-40% of cycle time (e.g., 1.2-1.6 seconds at 15 breaths/min)
- Adjust I:E ratio based on underlying pathology: lower for obstructive disease (longer expiration), higher for restrictive disease (longer inspiration) 1
Common Pitfalls
Avoid setting IPAPmax too low (<20 cm H₂O in adults), as this restricts the device's ability to deliver adequate pressure support when needed, essentially negating the advantage of volume-assured ventilation. Conversely, while 30 cm H₂O is the recommended maximum, patient comfort and tolerance should guide final settings—if patients consistently awaken complaining of excessive pressure, reduce to tolerable levels even if below optimal targets. 1
The target tidal volume of 8 mL/kg may need adjustment: slightly lower tidal volumes (6-7 mL/kg) with higher respiratory rates may improve tolerance in individual patients, particularly those with obstructive lung disease. 1