What is the recommended driving pressure target for adult ARDS patients and how should tidal volume, plateau pressure, and PEEP be set to achieve it?

Driving Pressure in ARDS: Target ≤15 cmH₂O

Maintain driving pressure (ΔP = plateau pressure - PEEP) at ≤15 cmH₂O in adult ARDS patients, as this parameter predicts mortality better than tidal volume or plateau pressure alone and represents the functional stress applied to the remaining aerated "baby lung." 1, 2

Why Driving Pressure Matters Most

• Driving pressure reflects the ratio of tidal volume to respiratory system compliance, indicating the actual functional lung size available for ventilation rather than predicted body weight 1
• In ARDS, the proportion of aerated lung is markedly decreased, making ΔP superior to other ventilatory parameters for predicting outcomes 1, 2
• Values exceeding 15 cmH₂O are associated with significantly increased mortality risk, with ΔP ≥18 cmH₂O specifically linked to right ventricular failure 3, 1
• A 1-SD increment in ΔP (approximately 7 cmH₂O) increases mortality with a relative risk of 1.41 (95% CI 1.31-1.51), even in patients receiving "protective" plateau pressures and tidal volumes 2

Algorithmic Approach to Achieve Target Driving Pressure

Step 1: Calculate Baseline Driving Pressure

• Measure plateau pressure during an inspiratory hold maneuver (requires adequate sedation/paralysis for accuracy) 1
• Calculate: ΔP = plateau pressure - PEEP 1
• If ΔP >15 cmH₂O, immediate adjustment is required 1

Step 2: Set Initial Ventilator Parameters

• Tidal volume: Start at 6 mL/kg predicted body weight (PBW) 4
• Plateau pressure ceiling: Maintain ≤30 cmH₂O as an absolute limit 4
• PEEP: For moderate-severe ARDS (PaO₂/FiO₂ ≤200 mmHg), use higher PEEP strategies (adjusted RR 0.90 for mortality reduction) 1, 4

Step 3: Adjust to Achieve ΔP ≤15 cmH₂O

If driving pressure exceeds 15 cmH₂O, follow this sequence:

1. Decrease tidal volume first: Reduce below 6 mL/kg PBW if necessary to achieve target ΔP 1
2. Increase PEEP: Recruit collapsed alveoli to improve respiratory system compliance and lower ΔP 1
3. Reassess: Recalculate ΔP after each adjustment 1

Step 4: Monitor Serial Changes

• Daily ΔP measurements are more informative than a single Day 1 value 5
• Patients maintaining ΔP <14 cmH₂O on Days 1-3 have significantly better 60-day survival compared to those with increasing ΔP 5
• An increment from Day 1 ΔP <14 to Day 3 ΔP ≥14 cmH₂O carries an adjusted hazard ratio of 1.96 (95% CI 1.11-3.44) for mortality 5

Critical Nuances and Caveats

When to Relax Strict Tidal Volume Targets

• Low driving pressure (≤15 cmH₂O) may allow relaxation of strict 6 mL/kg PBW targets in patients with conflicting clinical priorities, such as severe acidosis requiring higher minute ventilation 3, 1
• This flexibility is permissible only when ΔP remains within safe limits 3

The Plateau Pressure vs. Driving Pressure Debate

• While driving pressure is the strongest predictor in most analyses 2, one study found plateau pressure slightly superior when both were evaluated at standardized settings 24 hours after ARDS onset 6
• Practical resolution: Maintain both targets—plateau pressure ≤30 cmH₂O AND driving pressure ≤15 cmH₂O—as complementary safety limits 1, 4
• If plateau pressure exceeds 30 cmH₂O, further reduce tidal volume regardless of driving pressure 4

PEEP Optimization Controversy

• Individual changes in PEEP after randomization are not independently associated with survival unless they lead to reductions in ΔP (mediation effect P=0.001) 2
• Higher PEEP strategies reduce mortality specifically in moderate-severe ARDS (PaO₂/FiO₂ ≤200 mmHg) 1, 4
• Avoid: Increasing PEEP solely to lower ΔP without considering recruitability, as this may worsen outcomes if it increases dead space or hemodynamic compromise 7

Ventilation Mode Selection

• Use volume-controlled ventilation initially to facilitate precise measurement of plateau pressure and driving pressure 4
• Volume-controlled and pressure-controlled ventilation show no mortality difference when delivering the same tidal volume 3, 4
• Consider transitioning to pressure-controlled ventilation later during assisted breathing for improved patient comfort, but vigilantly monitor delivered tidal volumes to ensure they remain 4-8 mL/kg PBW 4

Rescue Strategies for Persistent Elevated Driving Pressure

If ΔP remains >15 cmH₂O despite optimizing tidal volume and PEEP:

• Prone positioning: >12 hours/day reduces mortality (RR 0.74) in severe ARDS 1
• Neuromuscular blockade: Consider for ≤48 hours when PaO₂/FiO₂ <150 mmHg 4
• ECMO: For refractory cases with persistent ΔP >15 cmH₂O despite all interventions 1

Common Pitfalls to Avoid

• Do not use actual body weight for tidal volume calculations; always use predicted body weight based on height, as lung size correlates with height, not weight 8
• Do not assume pressure-controlled ventilation guarantees fixed tidal volume; it requires vigilant monitoring as delivered volumes vary with changing compliance 4
• Do not routinely apply recruitment maneuvers without evidence of recruitability, as they do not reduce mortality and may cause harm 3
• Do not ignore the absolute plateau pressure ceiling of 30 cmH₂O even if driving pressure is acceptable 4