Is a bilevel mode setting of 30 cmH2O over 0 cmH2O on a Puritan Bennett (mechanical ventilator) considered Airway Pressure Release Ventilation (APRV)?

Is Bilevel 30/0 Considered APRV?

No, a bilevel mode setting of 30 cmH₂O over 0 cmH₂O on a Puritan Bennett ventilator is not technically APRV, though it shares some mechanical similarities—the critical distinguishing features of APRV are the timing parameters (prolonged high pressure time with brief release phases) and the specific physiologic intent, not just the pressure levels alone. 1, 2

Understanding the Distinction

What Defines APRV

APRV is fundamentally characterized by its timing strategy, not its pressure differential. 2, 3 The mode operates with:

• Prolonged time at high pressure (T_High): Typically several seconds to maintain continuous alveolar recruitment 2
• Brief release phase (T_Low): Usually 0.2-0.8 seconds, just long enough to allow CO₂ elimination without permitting alveolar collapse 2, 3
• Inverse ratio ventilation: Inspiratory time exceeds expiratory time, distinguishing it from conventional modes 1
• Unrestricted spontaneous breathing: Allowed throughout the entire respiratory cycle at both pressure levels 2, 4

The American Thoracic Society emphasizes that APRV utilizes this inverse ratio ventilation strategy specifically to increase alveolar recruitment and improve oxygenation in ARDS patients. 1

What You're Actually Seeing

Your bilevel 30/0 setting is more accurately described as bi-level pressure support or BiPAP in invasive mode. 5, 6 This configuration:

• Uses inspiratory positive airway pressure (IPAP) of 30 cmH₂O 6
• Uses expiratory positive airway pressure (EPAP) of 0 cmH₂O 5
• Likely has conventional I:E ratios (not inverse ratio) 1
• Functions as patient-triggered pressure support 6

The British Thoracic Society notes that bi-level pressure support combines IPAP for ventilation with EPAP to recruit underventilated lung and offset intrinsic PEEP. 1

Critical Technical Differences

Timing Parameters Matter Most

The defining feature separating APRV from bilevel modes is the T_Low setting. 2, 7 In true APRV:

• T_Low is personalized based on the slope of the expiratory flow curve (P-APRV approach) 2
• The release phase is intentionally brief (typically <1 second) to prevent alveolar de-recruitment 2, 3
• T_High is prolonged (often 4-6 seconds or longer) to maintain continuous positive pressure 3

Without knowing your T_High and T_Low settings, you cannot definitively call this APRV. 7 A 2024 meta-regression analysis demonstrated tremendous variation in what clinicians label as "APRV," with no standardized method to set the four individual parameters (P_High, P_Low, T_High, T_Low). 7

The Zero EPAP Concern

Your EPAP of 0 cmH₂O is atypical for both modern APRV and bilevel strategies. 1, 3

• APRV typically uses P_Low of 0-5 cmH₂O, but rarely zero in practice 3
• The European Respiratory Society recommends EPAP of 3-5 cmH₂O in bi-level support to offset intrinsic PEEP and recruit underventilated lung 5, 6
• Zero EPAP provides no expiratory pressure to maintain alveolar patency between release phases 1

Common Pitfalls to Avoid

Nomenclature Confusion

The terms BiPAP, bilevel, and APRV are often used interchangeably but represent distinct ventilation strategies. 4 A 1996 study noted that BiPAP and APRV are "technically closely related" but serve different clinical purposes—BiPAP facilitates spontaneous breathing and weaning, while APRV specifically targets alveolar recruitment in acute lung injury. 4

Setting Verification Needed

To determine if this is truly APRV, you must verify: 2, 7

• What is the T_High setting? (Should be prolonged, typically >4 seconds)
• What is the T_Low setting? (Should be brief, typically 0.2-0.8 seconds)
• Is the I:E ratio inverted? (Inspiratory time should exceed expiratory time)
• Is spontaneous breathing unrestricted throughout the cycle? 4

Clinical Context Matters

APRV is specifically indicated for ARDS patients with refractory hypoxemia or ventilator asynchrony. 1 The Society of Critical Care Medicine suggests considering APRV for ARDS patients when conventional lung-protective ventilation fails. 1

If your patient doesn't have ARDS or severe hypoxemia requiring aggressive recruitment strategies, this setting is almost certainly intended as bilevel pressure support, not APRV. 1, 8

Practical Recommendation

Check your ventilator's timing parameters immediately. 7 If T_High is prolonged (>4 seconds) and T_Low is very brief (<1 second), this may be an attempt at APRV. If the timing follows conventional ratios, you're looking at high-pressure bilevel support with zero PEEP—a setting that warrants clinical review given the lack of expiratory pressure support. 5, 6

The 30 cmH₂O pressure is concerning regardless of mode. 5 Ensure this high pressure is clinically justified and that plateau pressures remain <30 cmH₂O to minimize ventilator-induced lung injury risk. 1