Ventilator Settings for ARDS ("Leaky and Flooded Lung")
Use a tidal volume of 6 mL/kg predicted body weight (not actual weight), maintain plateau pressure ≤30 cmH₂O, and target driving pressure ≤15 cmH₂O as your primary ventilator goals in all ARDS patients. 1, 2, 3
Core Ventilator Parameters
Tidal Volume
- Set tidal volume at 6 mL/kg predicted body weight (PBW) as the foundation of lung-protective ventilation 1, 3
- Calculate PBW using height and sex, never actual body weight, even in obese patients 3
- This reduces mortality from 39.8% to 31.0% compared to traditional 12 mL/kg volumes 4
- You may need to reduce tidal volume below 6 mL/kg PBW if plateau pressure exceeds 30 cmH₂O 5
Plateau Pressure
- Maintain plateau pressure ≤30 cmH₂O as an absolute ceiling regardless of other parameters 1, 5
- Measure during inspiratory hold maneuver (requires adequate sedation/paralysis for accuracy) 2
- This limit prevents ventilator-induced lung injury from alveolar overdistension 5
Driving Pressure (The Most Important Parameter)
- Calculate driving pressure at bedside: ΔP = plateau pressure - PEEP 2
- Target driving pressure ≤15 cmH₂O as it predicts mortality better than tidal volume or plateau pressure alone 2, 5
- If ΔP >15 cmH₂O, immediately decrease tidal volume below 6 mL/kg PBW or increase PEEP 2
- Driving pressure ≥18 cmH₂O specifically increases right ventricular failure risk 2, 5
PEEP Strategy Based on ARDS Severity
Mild ARDS (PaO₂/FiO₂ 201-300)
- Use lower PEEP strategy (<10 cmH₂O) to optimize oxygenation while minimizing hemodynamic compromise 3
Moderate to Severe ARDS (PaO₂/FiO₂ ≤200)
- Use higher PEEP strategy (>10 cmH₂O) to recruit collapsed alveoli and improve compliance 1, 3, 5
- Higher PEEP reduces mortality (adjusted RR 0.90) in moderate-severe ARDS 2
- Titrate PEEP upward to achieve driving pressure ≤15 cmH₂O 2
- Monitor for hemodynamic compromise during PEEP titration 3
Adjunctive Strategies for Severe ARDS (PaO₂/FiO₂ <150)
Prone Positioning
- Implement prone positioning for >12 hours per day in severe ARDS 1, 3, 5
- This reduces mortality (RR 0.74) and is a strong recommendation 2, 3
- Use when driving pressure remains >15 cmH₂O despite optimization 2
Recruitment Maneuvers
- Consider recruitment maneuvers for refractory hypoxemia in moderate-severe ARDS 1, 5
- This is a conditional recommendation with low confidence in effect estimates 1
Neuromuscular Blockade
- Consider neuromuscular blocking agents for ≤48 hours when PaO₂/FiO₂ <150 mmHg 3, 5
- Improves ventilator synchrony and reduces work of breathing 3
Fluid Management
- Use conservative fluid strategy for established ARDS without tissue hypoperfusion 3, 5
- Avoid fluid overload as it worsens pulmonary edema and gas exchange 3
Permissive Hypercapnia
- Accept permissive hypercapnia when using lower tidal volumes to prevent alveolar overdistension 5
- This is necessary to maintain plateau pressure ≤30 cmH₂O 5
What to Avoid
- Never use high tidal volumes (>8 mL/kg PBW) as they increase ventilator-induced lung injury 3
- Do not routinely use high-frequency oscillatory ventilation in moderate or severe ARDS (strong recommendation against) 1, 3
- Avoid beta-2 agonists unless bronchospasm is present 3
Common Pitfalls
- Using actual body weight instead of predicted body weight leads to excessive tidal volumes in obese patients 3
- Focusing only on tidal volume while ignoring driving pressure misses the most important predictor of mortality 2
- Failing to measure plateau pressure prevents accurate assessment of lung stress 2
- Setting PEEP too low in moderate-severe ARDS wastes an opportunity to recruit lung and reduce driving pressure 2, 3