When to switch from Average Volume-assured Pressure Support (AVAPS) to Bilevel Positive Airway Pressure (BiPAP)?

When to Switch from AVAPS to BiPAP

The primary indication to switch from Average Volume-assured Pressure Support (AVAPS) to Bilevel Positive Airway Pressure (BiPAP) is when the patient no longer requires guaranteed tidal volumes but still needs respiratory support with pressure differentials. This typically occurs when the patient's respiratory status has stabilized and they can maintain adequate ventilation with standard pressure support.

Indications for Switching from AVAPS to BiPAP

• Patient comfort and tolerance: If the patient is uncomfortable with the variable inspiratory pressures of AVAPS but still requires bilevel support, switching to standard BiPAP may improve comfort 1
• Stabilized respiratory status: When a patient's respiratory drive has improved and they no longer require guaranteed tidal volumes 1
• Resolution of hypercapnic encephalopathy: Once a patient with altered mental status due to hypercapnia has improved consciousness and stable CO2 levels 2
• Improved ventilation parameters: When arterial blood gases show normalized or significantly improved pH and pCO2 levels 3
• Decreased work of breathing: When respiratory rate and effort have normalized 4

Clinical Parameters to Monitor When Considering the Switch

• Blood gas measurements: Normalized or significantly improved pH and pCO2 levels 3
• Level of consciousness: Improved Glasgow Coma Scale in patients who had hypercapnic encephalopathy 2
• Respiratory rate and pattern: Stable respiratory rate without signs of increased work of breathing 4
• Oxygen saturation: Maintained adequate SpO2 levels without significant desaturations 4
• Transcutaneous CO2 monitoring: Stable or improved CO2 levels 5

Algorithm for Decision-Making

1. Initial Assessment: Evaluate if the patient still requires non-invasive ventilation support

   • If no longer requiring NIV → discontinue respiratory support 1
   • If still requiring support → proceed to step 2

2. Evaluate Respiratory Stability:

   • Stable blood gases (pH > 7.35, normalized or improving pCO2) → consider switch to BiPAP 3
   • Unstable blood gases → continue AVAPS 3

3. Assess Volume Requirements:

   • If patient can maintain adequate minute ventilation without guaranteed volumes → switch to BiPAP 1
   • If patient still requires guaranteed tidal volumes → continue AVAPS 5

4. Evaluate Patient Comfort:

   • If patient reports discomfort with variable pressures of AVAPS → trial BiPAP 6
   • If patient is comfortable with current settings → maintain current mode 6

Special Considerations

• High pressure requirements: For patients requiring inspiratory pressures >20 cm H2O, BiPAP may be more appropriate than CPAP but should be determined during titration 1
• Pneumothorax: BiPAP should be withheld from patients with pneumothorax until it has resolved 1
• Hemoptysis: For patients with massive hemoptysis using BiPAP as chronic therapy, discontinue BiPAP as long as there is bleeding 1
• Neuromuscular disease: These patients may benefit from remaining on AVAPS long-term rather than switching to standard BiPAP due to their variable respiratory muscle strength 4

Common Pitfalls to Avoid

• Premature switching: Switching too early before respiratory status has stabilized may lead to hypoventilation and respiratory deterioration 3
• Inadequate monitoring: Failure to monitor blood gases after switching modes can miss early signs of decompensation 2
• Ignoring patient comfort: Patient comfort and synchrony with the ventilator are important factors in successful non-invasive ventilation 6
• Not adjusting settings: When switching from AVAPS to BiPAP, settings should be adjusted based on the average pressures delivered during AVAPS mode 1

Remember that the decision to switch from AVAPS to BiPAP should be based on objective clinical parameters showing improved respiratory status and the patient's ability to maintain adequate ventilation without guaranteed tidal volumes.