What do the AVAPS (Average Volume Assured Pressure Support) settings of Mode AE (Auto‑EPAP), target tidal volume 600 mL, and pressure support range 12–15 cm H₂O mean?

AVAPS Settings Explanation

These settings configure a volume-targeted bilevel ventilator that automatically adjusts inspiratory pressure to deliver a target tidal volume of 600 mL, while the "AE" mode automatically titrates expiratory pressure to maintain upper airway patency.

Mode AE (Auto-EPAP)

Mode AE refers to Average Volume Assured Pressure Support with Automated Expiratory Positive Airway Pressure 1. This is a sophisticated ventilation mode that combines two automated features:

• Auto-EPAP component: The ventilator automatically adjusts the expiratory positive airway pressure (EPAP) to eliminate obstructive respiratory events like apneas, hypopneas, and snoring—similar to how an auto-CPAP machine works 2, 3
• Volume-assured component: The machine automatically varies inspiratory pressure support (IPAP) within preset limits to achieve the target tidal volume 1

This dual automation means the ventilator is making real-time adjustments on both the inspiratory and expiratory phases without requiring manual titration.

Tidal Volume 600 mL

This is the target tidal volume the ventilator aims to deliver with each breath 1. The machine will automatically increase or decrease the inspiratory pressure support (within the 12-15 cm H₂O range specified below) to maintain this volume.

Key points about this setting:

• 600 mL represents approximately 6-8 mL/kg for a patient weighing 75-100 kg, which aligns with guideline recommendations 1
• If the patient's respiratory mechanics change (worsening compliance, increased airway resistance, or weakening respiratory muscles), the ventilator will increase pressure support to maintain this volume 1
• Conversely, if conditions improve, the machine will reduce pressure support while still delivering 600 mL

Pressure Support 12 over 15

This notation is somewhat ambiguous but most likely means:

Interpretation: Minimum IPAP of 12 cm H₂O and Maximum IPAP of 15 cm H₂O (with EPAP being automatically adjusted by the AE algorithm)

However, there's an alternative interpretation that needs consideration:

Alternative interpretation: IPAP range from 12-15 cm H₂O above a baseline EPAP (though this would be unusually high)

Most Likely Configuration:

Based on guideline recommendations for AVAPS settings 1:

• IPAPmin = 12 cm H₂O: The minimum inspiratory pressure the ventilator will deliver
• IPAPmax = 15 cm H₂O: The maximum inspiratory pressure allowed
• EPAP = Auto-adjusting (typically starting around 4-8 cm H₂O and adjusting based on upper airway obstruction)
• Pressure Support range = 4-11 cm H₂O (the difference between IPAP and EPAP, which varies as both parameters auto-adjust)

How This Works in Practice

Breath-by-breath operation:

1. The ventilator monitors delivered tidal volume continuously
2. If tidal volume falls below 600 mL, IPAP increases (up to the 15 cm H₂O maximum)
3. If tidal volume exceeds 600 mL, IPAP decreases (down to the 12 cm H₂O minimum)
4. Simultaneously, the AE algorithm monitors for obstructive events and adjusts EPAP accordingly 2, 3
5. The actual pressure support (IPAP minus EPAP) varies automatically based on both algorithms

Clinical Implications

Advantages of these settings:

• Reduces need for manual pressure adjustments during sleep or changing conditions 2, 3, 4
• Maintains adequate ventilation even if respiratory muscle strength declines 1
• Addresses both hypoventilation and upper airway obstruction simultaneously 2

Potential limitations:

• The narrow IPAP range (12-15 cm H₂O, only 3 cm H₂O window) may be insufficient if the patient requires higher pressures to achieve 600 mL tidal volume 1
• If the machine consistently operates at the maximum IPAP of 15 cm H₂O without achieving target volume, settings need adjustment
• The auto-EPAP algorithm may increase EPAP in response to obstructive events, which could narrow the effective pressure support range further

Common Pitfalls

Watch for these issues:

• Inadequate pressure range: If the ventilator consistently runs at IPAPmax (15 cm H₂O) and still doesn't achieve 600 mL, the maximum needs to be increased 1
• Excessive leak: High leak rates can confuse the volume-targeting algorithm and prevent accurate tidal volume delivery 5
• Patient-ventilator asynchrony: Despite automation, some patients may not synchronize well with the device, particularly those with neuromuscular disease or severe COPD 5
• Auto-EPAP limitations: While auto-EPAP improves comfort and reduces setup time 2, 3, it may not be optimal for all patients, particularly those with severe obesity hypoventilation syndrome who may benefit from higher fixed EPAP

Monitoring requirements:

• Downloaded data should show actual delivered tidal volumes averaging near 600 mL
• IPAP should vary within the 12-15 range (not consistently at maximum or minimum)
• EPAP levels should be reviewed to ensure they're appropriate for the patient's needs
• Transcutaneous or arterial PCO₂ should be monitored to confirm adequate ventilation 1