AVAPS Settings for a 66-inch Tall Male
For a 66-inch (5'6") tall male, start with EPAP = 4 cm H₂O, IPAP min = 8 cm H₂O (EPAP + 4), IPAP max = 25-30 cm H₂O, and target tidal volume = 440 mL (8 mL/kg ideal body weight). 1
Calculating Ideal Body Weight and Target Tidal Volume
For a 66-inch tall male:
- Ideal body weight (IBW) ≈ 55 kg (using standard IBW formulas for males at this height)
- Target tidal volume = 8 mL/kg × 55 kg = 440 mL
This calculation is based on the AASM consensus guideline recommendation of approximately 8 mL/kg ideal body weight for volume-targeted pressure support 1.
Initial AVAPS Settings Algorithm
Pressure Settings:
- EPAP: 4 cm H₂O (minimum available on most devices)
- IPAP min: 8 cm H₂O (EPAP + 4 cm H₂O minimum pressure support)
- IPAP max: 25-30 cm H₂O (allows device to auto-adjust as needed)
- Target Tidal Volume: 440 mL (8 mL/kg IBW)
If Using Spontaneous-Timed (ST) Mode:
- Backup rate: Set 2-4 breaths below patient's spontaneous rate (typically 12-15 breaths/min for adults)
- Inspiratory time: 1.2-1.6 seconds (corresponding to 30-40% IPAP time at respiratory rate of 15)
- I:E ratio: Minimum 1:2 (longer expiratory time if obstructive lung disease present) 1
Rationale and Evidence Strength
The AASM NPPV Titration Task Force guidelines 1 provide Level A consensus recommendations specifically for AVAPS (the only volume-targeted BPAP device available in the United States at the time of guideline publication). These settings ensure adequate pressure support while allowing the device's servo-mechanism to automatically adjust IPAP between the minimum and maximum limits to deliver the targeted tidal volume 1, 2.
The 8 mL/kg target is based on physiologic principles: during normal ventilation, tidal volumes of 6-8 mL/kg maintain adequate oxygenation and CO₂ elimination 1. The AVAPS mode's advantage is that it automatically increases pressure support if tidal volume drops (e.g., due to declining respiratory muscle strength or increased leak) and decreases it during hyperventilation 1, 2.
Titration Goals and Adjustments
Primary goals during AVAPS titration:
- Eliminate obstructive events: Adjust EPAP upward (following OSA titration guidelines) if apneas, hypopneas, RERAs, or snoring persist 1
- Achieve adequate ventilation: Confirm device delivers target tidal volume with acceptable pressure support
- Normalize gas exchange: Target SpO₂ ≥90% and PCO₂ ≤ awake baseline 1
Adjust target tidal volume if:
- Patient has restrictive lung disease: May tolerate slightly lower volumes (6-7 mL/kg) with higher respiratory rates
- Patient has significant dead space: May need higher minute ventilation
- Excessive leak present: Address mask fit before increasing pressures 1
Common Pitfalls to Avoid
Critical considerations:
- Verify IBW calculation: Using actual body weight instead of ideal body weight will result in excessive tidal volumes, particularly in obese patients
- Monitor for leak: High mask leak degrades flow signal accuracy, making device-estimated tidal volumes unreliable 1. If pressure support increases fail to raise tidal volume, suspect excessive leak
- Don't use BPAP without backup rate: Standard BPAP (without backup rate) can worsen central apneas and should be avoided 3. AVAPS inherently includes volume assurance but may still benefit from ST mode if central apneas are present
- Pressure support range matters: The 4 cm H₂O minimum pressure support allows adaptation, while the 20 cm H₂O maximum pressure support limit prevents over-ventilation 1
Mode Selection
Use spontaneous mode if patient has consistent spontaneous respiratory effort. Switch to ST mode if frequent central apneas develop during titration or if baseline central apneas are present 1.
The evidence comparing AVAPS to standard BPAP shows comparable efficacy in most populations 4, 5, 6, 7, with AVAPS potentially offering faster CO₂ clearance in acute hypercapnic respiratory failure 4, 5. However, this hasn't translated to improved mortality or reduced hospitalizations 6. The key advantage of AVAPS is automated pressure adjustment to maintain consistent tidal volume delivery, which may be particularly useful in patients with variable respiratory drive or changing respiratory mechanics 2.