Can NIV Be Used in Treatment of ARDS?
NIV can be cautiously considered only in selected patients with mild ARDS (PaO₂/FiO₂ 200-300 mmHg) who are hemodynamically stable, alert, and can be closely monitored in an ICU setting, but it should NOT be used routinely in moderate-to-severe ARDS due to high failure rates and risk of delayed intubation leading to increased mortality. 1, 2
Patient Selection Criteria for NIV in ARDS
NIV may be reasonable as an initial approach only when ALL of the following criteria are met:
- Mild ARDS only (PaO₂/FiO₂ 200-300 mmHg) 1, 3
- Hemodynamically stable without shock or vasopressor requirements 4, 3
- Alert and cooperative patient who can protect their airway 5
- SAPS II score < 34 2
- ARDS not caused by pneumonia (pneumonia-induced ARDS has particularly high NIV failure rates) 2, 6
- Younger patients with fewer comorbidities 2
- ICU setting with immediate intubation capability and highly skilled staff 4, 5
Absolute Contraindications to NIV in ARDS
NIV should NOT be used in the following situations:
- Moderate or severe ARDS (PaO₂/FiO₂ < 200 mmHg) - failure rates exceed 40-50% 3, 4
- Impaired consciousness or inability to protect airway 2
- Hemodynamic instability or shock requiring vasopressors 1, 3
- Copious respiratory secretions 2
- Multi-organ failure 1
- Recent facial/upper airway surgery 5
Critical Monitoring Requirements
When NIV is attempted in mild ARDS, the following intensive monitoring is mandatory:
- Arterial blood gas analysis at 1-2 hours and again at 4-6 hours if initial improvement is minimal 5
- Continuous assessment of respiratory rate and work of breathing 2
- Rapid Shallow Breathing Index (RSBI): if >105 breaths/min/L, intubation is likely needed 2
- Tidal volumes: if persistently >9.5 mL/kg predicted body weight, proceed to intubation 2
- Minute ventilation: if >11 L/min at 48 hours, this predicts NIV failure 6
- Clinical deterioration markers: worsening dyspnea, accessory muscle use, or altered mental status 2
Timing of Intubation
If there is no substantial improvement in gas exchange and respiratory rate within 4-6 hours despite optimal NIV settings, discontinue NIV immediately and proceed to invasive mechanical ventilation. 5, 2
Delayed intubation is associated with significantly increased mortality in patients with acute respiratory failure 2. The decision regarding intubation should be made and documented BEFORE starting NIV 5.
Evidence on NIV Failure Rates
The evidence demonstrates concerning failure rates:
- Overall NIV failure in ARDS: 43.75% in clinical practice 3
- Moderate ARDS: significantly higher failure and mortality rates 3
- Severe ARDS: NIV failure approaches 50-60% 4, 3
- Pneumonia-induced mild ARDS: NIV did not reduce intubation rates compared to standard oxygen (10.8% vs 9.2%) despite improved oxygenation 6
Special Consideration: Helmet NIV
One study showed that helmet NIV (rather than face mask) was associated with reduced intubation rates and 90-day mortality in ARDS patients 2. However, this was a single-center trial and requires confirmation before widespread adoption.
High-Flow Nasal Cannula as Alternative
High-flow nasal cannula (HFNC) may be superior to face-mask NIV in hypoxemic respiratory failure, with one trial showing significantly lower intubation rates with HFNC compared to NIV in patients with PaO₂/FiO₂ ≤200 mmHg 2, 1. HFNC should be started at 30-40 L/min with FiO₂ 50-60%, and escalation considered if FiO₂ >70% and flow >50 L/min for >1 hour 1.
Risk of Patient Self-Inflicted Lung Injury
A critical concern with NIV in ARDS is that spontaneous breathing with high respiratory drive may generate excessive transpulmonary pressure swings, potentially causing patient self-inflicted lung injury 2. This risk is particularly high in moderate-to-severe ARDS where respiratory drive is markedly elevated.
Standard of Care Recommendation
For moderate-to-severe ARDS (PaO₂/FiO₂ <200 mmHg), proceed directly to endotracheal intubation in a controlled setting and implement lung-protective ventilation with tidal volumes 4-8 mL/kg predicted body weight, plateau pressure ≤30 cmH₂O, and appropriate PEEP 1, 7. This approach avoids the risks of NIV failure and delayed intubation.