How do I adjust Airway Pressure Release Ventilation (APRV) settings for a patient?

Adjusting APRV Settings

APRV (Airway Pressure Release Ventilation) should be adjusted using the Time-Controlled Adaptive Ventilation (TCAV) method, which personalizes the release time (T-Low) based on the expiratory flow curve, terminating at 75% of peak expiratory flow to prevent alveolar collapse while maintaining high CPAP (P-High) for extended periods to recruit and stabilize the lung. 1

Understanding APRV Fundamentals

APRV functions as continuous positive airway pressure (CPAP) with brief intermittent releases, allowing spontaneous breathing throughout the entire respiratory cycle 2, 3. The mode maintains patients near their functional residual capacity by using high airway pressures to recruit lung volume, with brief releases providing metabolic support for CO2 clearance 3.

The core principle is "open the lung and keep it open" - the prolonged high-pressure phase (P-High/T-High) recruits collapsed alveoli, while the minimal release duration (P-Low/T-Low) prevents re-collapse 2.

Initial APRV Settings

P-High (High CPAP Level)

• Start at 20-30 cmH2O, adjusting based on plateau pressures from prior conventional ventilation 1
• Target maintaining lung recruitment without overdistension 1
• This represents the primary pressure maintaining alveolar stability 3

T-High (Time at High Pressure)

• Set at 4-6 seconds initially to allow prolonged recruitment time 1
• This extended inspiratory time is critical for gradual lung recruitment over hours to days 1
• Represents 80-95% of the total breath cycle 2

P-Low (Release Pressure)

• Set at 0-5 cmH2O to allow adequate CO2 clearance 1
• Lower pressures facilitate better ventilation during the release phase 1

T-Low (Release Time) - THE CRITICAL ADJUSTMENT

• Set to terminate expiratory flow at 75% of peak expiratory flow (EFV75) 1
• This is the most important personalized parameter that adapts to individual patient lung mechanics 1
• Typically ranges from 0.2-0.8 seconds 1
• Acts as a "brake" preventing newly recruited alveoli from collapsing 1

Step-by-Step Adjustment Algorithm

1. Optimizing T-Low (Primary Adjustment)

• Monitor the expiratory flow curve on the ventilator display 1
• Measure peak expiratory flow rate at the start of the release 1
• Calculate 75% of peak flow and adjust T-Low so expiratory flow terminates at this point 1
• If flow reaches zero before the next P-High cycle, T-Low is too long (risk of alveolar collapse) 1
• If flow is still high when P-High resumes, T-Low is too short (inadequate CO2 clearance) 1

This adjustment is adaptive and personalized - as lung compliance improves with recruitment, elastance changes, requiring T-Low readjustment every 2-4 hours 1.

2. Adjusting P-High for Oxygenation

• Increase P-High by 2-3 cmH2O if SpO2 remains <90% despite adequate FiO2 1
• Maximum P-High typically 35 cmH2O to avoid overdistension 1
• Monitor for hemodynamic compromise as high intrathoracic pressure reduces venous return 4

3. Adjusting T-High for Recruitment

• Maintain T-High at 4-6 seconds for optimal recruitment 1
• Longer T-High (up to 10 seconds) may be used in severe ARDS with extensive collapse 1
• Avoid shortening T-High as this defeats the recruitment strategy 1

4. Managing Hypercarbia

• First, verify T-Low is optimized (terminating at EFV75) 1
• If PaCO2 remains elevated, slightly increase T-Low by 0.1-0.2 seconds to allow more complete exhalation 5
• Alternatively, increase release frequency by shortening T-High (though this compromises recruitment) 5
• In refractory cases, adding pressure support during spontaneous breaths can reduce CO2 5

5. Weaning APRV

• As lung recruitment improves and spontaneous breathing increases, patients manage their own ventilatory needs 3
• When release breaths are no longer needed for CO2 clearance, transition to CPAP by eliminating releases 3
• This indicates successful lung recruitment and readiness for liberation 3

Critical Monitoring Parameters

• Expiratory flow curve morphology - the primary guide for T-Low adjustment 1
• PaCO2 and pH - assess adequacy of release phase 5
• SpO2 and P/F ratio - assess recruitment efficacy 5
• Hemodynamic parameters - PCWP and CVP increase linearly with P-High 4
• Spontaneous breathing effort - should be preserved throughout 3

Common Pitfalls and How to Avoid Them

Fixed Settings (F-APRV) vs. Personalized Settings (P-APRV)

Avoid using fixed T-Low settings that don't adapt to changing lung mechanics 2. Studies show P-APRV (using EFV75 method) demonstrates superior lung protection compared to fixed-setting approaches 2. The 30-year literature review shows tremendous variation in APRV definitions, with P-APRV showing the most consistent benefit in reducing ARDS incidence 2.

Inadequate Release Time

Setting T-Low too short prevents adequate CO2 clearance, while too long allows alveolar collapse 1. Always use the expiratory flow curve, not arbitrary time values 1.

Premature Abandonment

APRV recruitment occurs gradually over hours to days, not minutes 1. Maintain settings for at least 24-48 hours before declaring failure 5, 1.

Hemodynamic Misinterpretation

Pulmonary capillary wedge pressure (PCWP) accurately reflects left atrial pressure during APRV, but may not accurately reflect volume status due to high intrathoracic pressure 4. Interpret filling pressures cautiously and consider dynamic assessments 4.

Use in COPD

While not traditionally recommended as primary ventilation in COPD, APRV can be effective in refractory hypercarbia when conventional modes fail 5. In COPD patients with severe hypercarbia (PaCO2 >170 mmHg), consider APRV with optimized T-Low for adequate exhalation time 5.

Contraindications and Cautions

• Severe hemodynamic instability - high mean airway pressure reduces cardiac output 4
• Uncontrolled intracranial hypertension - elevated intrathoracic pressure may worsen ICP 3
• Large bronchopleural fistula - prolonged high pressure increases air leak 3