What are the ventilation modalities used for Acute Respiratory Distress Syndrome (ARDS)?

What is ARDS and Ventilation Modalities

Definition of ARDS

Acute Respiratory Distress Syndrome (ARDS) is a life-threatening form of respiratory failure characterized by inflammatory pulmonary edema resulting in severe hypoxemia. 1 The severity is classified by the PaO₂/FiO₂ ratio into three mutually exclusive categories: mild (201-300 mmHg), moderate (101-200 mmHg), and severe (<100 mmHg). 1

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Core Ventilation Strategy: Lung-Protective Ventilation (Universal for All ARDS)

All patients with ARDS must receive lung-protective mechanical ventilation with tidal volumes of 4-8 mL/kg predicted body weight and plateau pressures strictly below 30 cmH₂O. 1 This is a strong recommendation with moderate confidence in effect estimates. 1

Specific Parameters:

• Tidal volume: Target 6 mL/kg PBW (acceptable range 4-8 mL/kg PBW) 2
• Plateau pressure: Maintain <30 cmH₂O at all times 1, 2
• Predicted body weight calculation: Males = 50 + 0.91 × [height (cm) - 152.4] kg; Females = 45.5 + 0.91 × [height (cm) - 152.4] kg 2
• Permissive hypercapnia: Accept elevated CO₂ as a consequence of lung protection, maintaining pH >7.20 2

Critical pitfall: Do not prioritize normocapnia over lung-protective ventilation—accept permissive hypercapnia as necessary. 2 Do not use tidal volumes >8 mL/kg PBW even if plateau pressures appear acceptable—both parameters must be optimized simultaneously. 2

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PEEP Strategy: Titrate to ARDS Severity

For moderate-to-severe ARDS (PaO₂/FiO₂ <200 mmHg), use higher PEEP levels (typically >10 cmH₂O); for mild ARDS (PaO₂/FiO₂ 200-300 mmHg), lower PEEP may be appropriate. 2 This is a conditional recommendation with moderate confidence. 1

Implementation:

• Moderate/severe ARDS: Higher PEEP strategy is suggested 1, 2
• Mild ARDS: Lower PEEP (<10 cmH₂O) may be used, particularly in patients with cirrhosis or hemodynamic instability to avoid impairing venous return 2
• Monitoring: Watch for barotrauma when using PEEP >10 cmH₂O 2

The evidence shows no mortality difference between higher versus lower PEEP strategies in general ARDS populations 3, but subgroup analyses suggest benefit in more severe disease. 1, 4

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Prone Positioning: Mandatory for Severe ARDS

For severe ARDS with PaO₂/FiO₂ <150 mmHg, implement prone positioning for at least 12-16 hours daily. 1, 2 This is a strong recommendation with moderate-high confidence. 1

Evidence and Implementation:

• Mortality benefit: Prone positioning reduces mortality (RR 0.74) in severe ARDS when used >12 hours/day 1, 2
• Duration matters: Trials with >12 hours/day proning showed mortality benefit; shorter durations did not 1, 2
• Mechanism: Improves ventilation-perfusion matching, increases end-expiratory lung volume, and decreases ventilator-induced lung injury through more uniform tidal volume distribution 1
• Risks: Higher rates of endotracheal tube obstruction (RR 1.76) and pressure sores (RR 1.22) 1

Critical pitfall: Do not delay prone positioning in severe ARDS—early implementation improves outcomes. 2

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Neuromuscular Blockade: Early Use in Severe ARDS

For early severe ARDS with PaO₂/FiO₂ <150 mmHg, use neuromuscular blocking agents for up to 48 hours. 2

Implementation:

• Preferred method: Administer as intermittent boluses rather than continuous infusion when possible 2
• Continuous infusion indications: Persistent ventilator dyssynchrony, need for deep sedation, prone positioning, or persistently high plateau pressures 2

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Recruitment Maneuvers: Conditional Use

Recruitment maneuvers may be considered in patients with moderate or severe ARDS, but this is a conditional recommendation with low confidence in effect estimates. 1

Critical pitfall: Do not use recruitment maneuvers routinely or for prolonged periods—these are associated with harm. 2

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Interventions Strongly Recommended AGAINST

Do not use high-frequency oscillatory ventilation (HFOV) in patients with moderate or severe ARDS. 1, 2 This is a strong recommendation against routine use with high confidence in effect estimates. 1 While HFOV may be considered as rescue therapy in refractory cases 4, early use shows no benefit and potential harm. 1

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Adjunctive Therapies

Corticosteroids:

Administer systemic corticosteroids to mechanically ventilated patients with ARDS. 2 This is a conditional recommendation with moderate certainty of evidence. 2

Fluid Management:

Use a conservative fluid strategy in established ARDS without tissue hypoperfusion. 2, 5 Conservative fluid management improves ventilator-free days without increasing non-pulmonary organ failures. 2

Oxygenation Targets:

Target SpO₂ of 88-95% to avoid hyperoxia while maintaining adequate oxygenation. 2 Start supplemental oxygen if SpO₂ <92%, and maintain SpO₂ no higher than 96%. 2

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Rescue Therapy: ECMO

For severe refractory ARDS despite optimized ventilation, proning, and rescue therapies, consider venovenous ECMO in carefully selected patients at experienced centers. 2, 5 This should only be considered in carefully selected patients due to its resource-intensive nature. 2

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Summary Algorithm by ARDS Severity

All ARDS (Mild, Moderate, Severe):

• Lung-protective ventilation: 4-8 mL/kg PBW, plateau pressure <30 cmH₂O 1, 2
• Conservative fluid strategy 2
• Target SpO₂ 88-95% 2

Moderate ARDS (PaO₂/FiO₂ 101-200):

• Add higher PEEP (>10 cmH₂O) 1, 2
• Consider recruitment maneuvers 1

Severe ARDS (PaO₂/FiO₂ <100-150):

• Add prone positioning ≥12-16 hours/day 1, 2
• Add neuromuscular blockade for 48 hours 2
• Higher PEEP strategy 1, 2
• If refractory: Consider ECMO at experienced centers 2, 5