From the Guidelines
For ARDS, I recommend using a lung-protective ventilation strategy with low tidal volumes of 4-6 mL/kg of predicted body weight and plateau pressures maintained below 30 cmH2O, as supported by the most recent guidelines 1. This approach is crucial in minimizing ventilator-induced lung injury by preventing alveolar overdistention and cyclic atelectasis, which can worsen inflammation and damage.
Key Ventilator Settings:
- Tidal volume: 4-6 mL/kg of predicted body weight
- Plateau pressure: below 30 cmH2O
- PEEP: initially set between 10-15 cmH2O, adjusting based on oxygenation response and hemodynamic tolerance
- Target SpO2: 88-95% with FiO2 as low as possible to minimize oxygen toxicity
- Respiratory rate: adjusted to maintain pH >7.25 while being mindful of auto-PEEP
Additional Considerations:
- Prone positioning for 16+ hours daily if PaO2/FiO2 ratio remains <150 despite optimized ventilation
- Neuromuscular blockade with cisatracurium for up to 48 hours may be beneficial for severe, refractory hypoxemia
- Higher PEEP helps recruit collapsed alveoli while the permissive hypercapnia strategy avoids excessive ventilation pressures that could cause further injury, as suggested by recent guidelines 1. The use of corticosteroids, venovenous extracorporeal membrane oxygenation (VV-ECMO), and neuromuscular blockers may also be considered in specific cases, as outlined in the updated guidelines 1.
From the Research
Ventilator Settings for ARDS
The optimal ventilator settings for patients with Acute Respiratory Distress Syndrome (ARDS) are crucial to improve outcomes and reduce ventilator-induced lung injury (VILI).
- Tidal Volume: A low tidal volume strategy (≈3 ml/kg) combined with extracorporeal CO2 removal has been investigated as a potential approach to reduce VILI 2. However, the ARDS Network recommends a tidal volume of 6 ml/kg of predicted body weight 3.
- Positive End-Expiratory Pressure (PEEP): High PEEP levels set above the lower inflection point of the pressure-volume curve of the respiratory system (Pflex) have been shown to improve outcomes in patients with severe and persistent ARDS 4. The NIH ARDS Clinical Trials Network PEEP/FIO2 tables provide a guide to balancing PEEP and FIO2 settings in adults 3.
- Individualization of Ventilator Settings: Electrical impedance tomography (EIT) can be used to individualize PEEP and tidal volume settings in ARDS patients, allowing for optimization of ventilator settings without causing lung overdistension 5.
- Common Practice: Despite recommendations, ED physicians often initiate mechanical ventilation with high tidal volumes in patients at risk for ARDS, with an average of 1.5 mL/kg above the recommended tidal volume 6.
Key Considerations
- The use of very low tidal volumes combined with extracorporeal CO2 removal may have the potential to further reduce VILI compared with a 'normal' lung protective management 2.
- A mechanical ventilation strategy with a PEEP level set above Pflex and a low tidal volume can have a beneficial impact on outcome in patients with severe and persistent ARDS 4.
- Individualization of ventilator settings using EIT can lead to improved oxygenation and reduced alveolar cycling without promoting global overdistension 5.