What is AVAPS (Average Volume-Assured Pressure Support)?

What is AVAPS (Average Volume-Assured Pressure Support)?

AVAPS is a specialized mode of non-invasive ventilation that automatically adjusts inspiratory pressure within set limits (IPAP min to IPAP max) to deliver a targeted tidal volume, providing consistent ventilation despite changes in patient respiratory mechanics. 1

Definition and Mechanism

AVAPS combines features of both pressure-targeted and volume-targeted ventilation:

• It functions as a form of Volume-Targeted Bilevel Positive Airway Pressure (VT-BPAP)
• The ventilator automatically adjusts the inspiratory pressure support (IPAP) between preset minimum and maximum limits
• The goal is to maintain a consistent target tidal volume (typically set at approximately 8 mL/kg ideal body weight)
• Can be used in spontaneous, spontaneous-timed (S/T), or timed modes 1

Key Technical Parameters

When setting up AVAPS, the following parameters must be configured:

• EPAP (Expiratory Positive Airway Pressure): Typically starting at 4 cm H₂O
• IPAP min: Usually set at EPAP + 4 cm H₂O
• IPAP max: Typically set between 25-30 cm H₂O
• Target tidal volume: Approximately 8 mL/kg ideal body weight 1

If using AVAPS in ST or timed modes, additional parameters include:

• Backup respiratory rate
• Inspiratory time or %IPAP time (percentage of respiratory cycle spent in inspiration)

Clinical Applications

AVAPS is particularly beneficial in conditions characterized by:

1. Variable respiratory mechanics: The system can compensate for changes in respiratory muscle strength or compliance
2. Chronic hypoventilation syndromes: Including obesity hypoventilation syndrome, neuromuscular disorders, and COPD
3. Nocturnal hypoventilation: Especially in pediatric patients with various underlying conditions 2

Clinical Evidence and Benefits

AVAPS has demonstrated several advantages in clinical studies:

• Improved CO₂ clearance: In patients with COPD and hypercapnic encephalopathy, AVAPS showed more efficient reduction in pCO₂ compared to conventional BiPAP S/T 3
• Faster recovery of consciousness: In hypercapnic encephalopathy, AVAPS facilitated more rapid improvement in Glasgow Coma Scale scores 3
• Better ventilation stability: AVAPS delivers more consistent tidal volumes despite changes in patient condition 4
• Reduced hospital stay: In acute exacerbation of COPD with type 2 respiratory failure, AVAPS resulted in shorter hospital stays compared to conventional BiPAP 5

Practical Considerations

When implementing AVAPS, clinicians should consider:

• Patient selection: Most beneficial in patients with variable respiratory mechanics or those who fail conventional NIV
• Monitoring requirements: Regular assessment of arterial blood gases, ventilator parameters, and patient comfort
• Titration approach: The EPAP should be adjusted to eliminate obstructive events, while the target volume ensures adequate ventilation 1

Limitations and Pitfalls

• AVAPS may lead to higher peak pressures to maintain the target volume, potentially causing discomfort
• Patient-ventilator asynchrony can occur if settings are not optimized
• Limited long-term data on outcomes compared to conventional NIV modes
• May not be available on all ventilator platforms (historically was only available on Philips-Respironics devices) 1

AVAPS represents an important advancement in non-invasive ventilation technology by providing the stability of volume-targeted ventilation with the comfort and leak compensation of pressure-targeted systems, making it particularly valuable for patients with chronic respiratory failure requiring long-term ventilatory support.