How do you set the inspiratory pressure on Airway Pressure Release Ventilation (APRV) for an adult patient with severe respiratory failure, such as acute respiratory distress syndrome (ARDS), in an intensive care unit (ICU) setting?

Setting Inspiratory Pressure on APRV

Yes, you absolutely set the inspiratory pressure on APRV—it is called P-high (or P-high), and it represents the upper continuous positive airway pressure level that is maintained for the majority of the respiratory cycle. 1, 2, 3

Understanding APRV Pressure Settings

APRV operates using two pressure levels that you must set explicitly 2, 3:

• P-high (inspiratory pressure): The high continuous positive airway pressure maintained during T-high (the prolonged inspiratory phase)
• P-low (expiratory pressure): The lower pressure during T-release (the brief expiratory release phase)

The difference between P-high and P-low, combined with the timing settings, determines the ventilation strategy. 2, 3

Initial P-high Setting Strategy

Start P-high at 20-30 cmH₂O based on the severity of lung injury and the patient's plateau pressure requirements from prior conventional ventilation. 4, 3 The goal is to achieve adequate oxygenation while maintaining lung recruitment throughout the prolonged T-high phase.

• For moderate ARDS: Begin with P-high of 20-25 cmH₂O 3
• For severe ARDS: May require P-high of 25-30 cmH₂O 4, 3
• Critical caveat: P-high should not routinely exceed 30 cmH₂O, as this violates lung-protective ventilation principles established for ARDS 5, 6

Titrating P-high for Optimal Recruitment

Adjust P-high based on oxygenation response and driving pressure considerations 4, 3:

• Monitor SpO₂ and PaO₂/FiO₂ ratio—target SpO₂ 92-97% or PaO₂ 70-90 mmHg 6
• Calculate effective driving pressure: (P-high minus P-low) should ideally remain ≤15 cmH₂O 6, 7
• If oxygenation remains inadequate, increase P-high in 2-3 cmH₂O increments rather than increasing FiO₂ above 0.6 4

Critical Distinction: P-high vs. Plateau Pressure

A major pitfall is confusing P-high with plateau pressure—they are fundamentally different 2, 3:

• P-high is the set inspiratory pressure maintained continuously during T-high
• Plateau pressure in conventional ventilation reflects end-inspiratory alveolar pressure after a pause
• During APRV, if the patient takes spontaneous breaths on top of P-high, the actual transpulmonary pressure and tidal volume can exceed intended targets, potentially causing ventilator-induced lung injury 2

This is a critical safety concern: spontaneous inspiratory efforts during T-high can generate much larger tidal volumes than clinician-intended, with unknown consequences for alveolar stretch and injury. 2

P-low Setting (Expiratory Pressure)

Set P-low at 0-5 cmH₂O to allow adequate lung deflation during the brief release phase 3:

• P-low of 0 cmH₂O is commonly used 3
• Higher P-low (5 cmH₂O) may prevent excessive derecruitment in severe ARDS 4

Time Settings That Complement Pressure Settings

The T-high and T-low (or T-release) settings are equally critical and directly interact with your pressure settings 1, 4, 3:

• T-high: Set at 4-6 seconds to maintain recruitment 3
• T-low (T-release): This is where personalized APRV differs from fixed APRV 1, 4
  • Personalized APRV (P-APRV): Set T-release to terminate at 75% of peak expiratory flow on the flow-time curve—this prevents derecruitment while allowing adequate CO₂ clearance 1, 4
  • Fixed APRV (F-APRV): Uses arbitrary T-release of 0.4-0.8 seconds, which may not match individual lung mechanics 1, 3

Evidence Quality and Clinical Outcomes

There is no high-quality evidence that APRV improves mortality or other patient-centered outcomes compared to conventional lung-protective ventilation 8, 2, 3:

• No randomized controlled trials demonstrate superiority of APRV over volume-controlled ventilation with 6 mL/kg tidal volumes and plateau pressure <30 cmH₂O 8, 2
• Animal studies suggest potential benefits for alveolar recruitment and reduced lung injury, but human data are lacking 1, 4
• The tremendous variation in APRV settings across studies makes it impossible to assess efficacy of any single strategy 1

When APRV May Be Considered

APRV is primarily used as rescue therapy for refractory hypoxemia in severe ARDS when conventional lung-protective ventilation fails 3:

• Consider only after optimizing conventional ventilation (6 mL/kg tidal volume, plateau pressure <30 cmH₂O, higher PEEP strategies, prone positioning) 5, 6
• Requires institutional expertise and protocols to ensure safe implementation 8
• Major risk: Without precise settings and monitoring, APRV has greater potential to worsen outcomes than improve them 8

Monitoring Requirements After Setting Pressures

Vigilant monitoring is mandatory because APRV performance depends entirely on operator-selected settings and patient response 8, 2:

• Continuously monitor delivered tidal volumes—spontaneous breaths during T-high can generate excessive volumes (>8 mL/kg PBW) 2
• Assess driving pressure (P-high minus P-low) and keep ≤15 cmH₂O 6, 7
• Monitor for auto-PEEP by examining expiratory flow curves 4
• Watch for hemodynamic compromise from elevated mean airway pressure 2, 3

Bottom Line for Clinical Practice

Set P-high as your inspiratory pressure (typically 20-30 cmH₂O), but recognize that APRV lacks outcome data supporting its use over conventional lung-protective ventilation. 5, 8, 2 Unless you have institutional protocols, expertise, and a patient with refractory hypoxemia despite optimized conventional strategies, standard volume-controlled ventilation with 6 mL/kg tidal volumes and plateau pressure <30 cmH₂O remains the evidence-based approach. 5, 6