What are the ideal mechanical ventilation settings, specifically peak systolic pressure (PS) in relation to positive end-expiratory pressure (PEEP), for an adult patient with acute respiratory distress syndrome (ARDS)?

Pressure Support Above PEEP in ARDS

In pressure support ventilation for ARDS patients, set the pressure support level to achieve a tidal volume of 6 mL/kg predicted body weight (range 4-8 mL/kg PBW), while ensuring the resulting plateau pressure remains ≤30 cm H₂O and driving pressure (plateau minus PEEP) stays ≤15 cm H₂O. 1, 2

Fundamental Ventilator Parameters

The pressure support level must be titrated to deliver lung-protective ventilation parameters:

• Target tidal volume of 6 mL/kg PBW as the primary goal when setting pressure support, with an acceptable range of 4-8 mL/kg PBW 1, 2
• Maintain plateau pressure ≤30 cm H₂O as an absolute ceiling to prevent overdistention and ventilator-induced lung injury 1, 2
• Target driving pressure (plateau - PEEP) ≤15 cm H₂O, as this parameter predicts outcomes better than other ventilatory variables 2, 3

PEEP Selection Based on ARDS Severity

The PEEP component must be set according to disease severity before determining the pressure support level above it:

• For moderate to severe ARDS (PaO₂/FiO₂ <200 mm Hg): Use higher PEEP levels of 10-15 cm H₂O, as individual patient data meta-analysis demonstrated mortality reduction with mean PEEP of 15.1 ± 3.6 cm H₂O versus 9.1 ± 2.7 cm H₂O (adjusted RR 0.90,95% CI 0.81-1.00) 1, 3

• For mild ARDS (PaO₂/FiO₂ 200-300 mm Hg): Use lower PEEP <10 cm H₂O, as higher PEEP showed no mortality benefit and potential harm in this subgroup (adjusted RR 1.29,95% CI 0.91-1.83) 1, 3

• Minimum PEEP of 5 cm H₂O should be applied universally to all mechanically ventilated patients to prevent alveolar collapse and atelectasis 3

Calculating the Pressure Support Level

Once PEEP is set appropriately, the pressure support level above PEEP is determined by:

1. Start with a pressure support level that achieves 6 mL/kg PBW tidal volume 1, 2
2. Measure the resulting plateau pressure (pressure support + PEEP = plateau pressure in a passively inflated lung) 1
3. Calculate driving pressure (plateau pressure minus PEEP) and ensure it remains ≤15 cm H₂O 2, 3
4. Adjust pressure support downward if plateau exceeds 30 cm H₂O, even if this results in lower tidal volumes, as the plateau pressure ceiling takes priority 1, 2

Mechanical Power Considerations

The total mechanical power delivered to the respiratory system should be monitored:

• Calculate mechanical power using the simplified formula: 0.098 × Respiratory Rate × Tidal Volume (L) × (PEEP + Driving Pressure) 2
• Target mechanical power <17 J/min, and definitely keep <22 J/min to minimize ventilator-induced lung injury 2
• This calculation integrates all ventilator parameters including your pressure support and PEEP settings 2

Critical Monitoring Parameters

When using pressure support ventilation in ARDS:

• Monitor plateau pressure continuously to ensure it stays ≤30 cm H₂O, as this is the strongest predictor of ventilator-induced lung injury 1
• Assess driving pressure at each ventilator adjustment, targeting ≤15 cm H₂O 2, 3
• Verify tidal volumes remain in the 4-8 mL/kg PBW range 1, 2
• Evaluate oxygenation response to PEEP changes, as higher PEEP improves PaO₂/FiO₂ ratio by approximately 50-60 mm Hg in moderate-severe ARDS 1

Common Pitfalls to Avoid

• Do not use zero PEEP (ZEEP) in any mechanically ventilated patient, as it leads to alveolar collapse 3
• Do not prioritize oxygenation alone when setting PEEP, as oxygenation-based PEEP titration is not congruent with the PEEP levels necessary to maintain lung stability 4, 5
• Do not apply high PEEP to mild ARDS, as this may increase mortality without benefit 1, 3
• Do not exceed plateau pressure of 30 cm H₂O even to achieve target tidal volumes, as overdistention causes harm 1, 2