Recommended NIV Modality
For acute respiratory failure requiring non-invasive ventilation, use bi-level pressure support ventilators (BiPAP) as the first-line modality, with IPAP starting at 10-15 cmH₂O and EPAP at 4-8 cmH₂O. 1, 2
Primary Recommendation: Bi-Level Pressure Support
Bi-level pressure support ventilators are the preferred NIV modality because they are simpler to use, cheaper, more flexible than other ventilator types, and have been used in the majority of randomized controlled trials demonstrating efficacy in acute hypercapnic respiratory failure. 1
Initial Settings for Bi-Level Pressure Support:
- IPAP (Inspiratory Positive Airway Pressure): Start at 10-15 cmH₂O 2
- EPAP (Expiratory Positive Airway Pressure): Start at 4-8 cmH₂O 2
- Pressure differential: Maintain at least 5 cmH₂O between IPAP and EPAP 2
- Backup respiratory rate: Set at 10-14 breaths/min 2
- FiO₂: Titrate to maintain SpO₂ between 85-90% (especially in COPD) 1, 2
Why Bi-Level Pressure Support Works:
The bi-level system provides two distinct advantages: IPAP assists inspiration and reduces work of breathing, while EPAP eliminates exhaled air through the expiratory port (reducing rebreathing), encourages lung recruitment, stents open the upper airway, and in COPD patients specifically overcomes intrinsic PEEP. 1 This dual-pressure approach has been validated in most recent randomized controlled trials showing reduced intubation rates and mortality in acute hypercapnic respiratory failure. 1, 3
Alternative Modality: CPAP (Continuous Positive Airway Pressure)
Use CPAP instead of bi-level support only for cardiogenic pulmonary edema where the primary problem is hypoxemia rather than hypercapnia. 1, 3
CPAP Settings:
- Fixed pressure: 10 cmH₂O is the most commonly used level 1, 4
- Indication: Patients with cardiogenic pulmonary edema who remain hypoxic despite maximal medical treatment 1
CPAP is simpler and more readily available than bi-level support, but reserve NIV (bi-level) for patients in whom CPAP is unsuccessful or when respiratory acidosis develops. 1, 3
Volume-Controlled Ventilators: Reserve for Complex Cases
Volume-controlled ventilators should be available in units providing comprehensive acute NIV services but are not first-line. 1 Consider volume control only when:
- Patients fail pressure-timed support despite optimization 1
- Compliance or airway resistance changes significantly 1
- More difficult patients require guaranteed alveolar ventilation 1
The disadvantage is that volume ventilators require arbitrary increases in tidal volumes to compensate for inevitable air leaks, and they provide greater patient discomfort compared to pressure support. 1
Critical Implementation Points
Mode Selection (Spontaneous vs. Timed):
- Start with spontaneous/timed (S/T) mode rather than pure pressure support 1
- This provides mandatory breaths if the patient stops triggering, which is essential for patients with advanced respiratory failure who may cease respiratory effort, those dependent on hypoxic drive, or neuromuscular disease patients with insufficient effort to trigger breaths 1
Monitoring for Success or Failure:
- Recheck arterial blood gases after 1-2 hours of NIV initiation 2, 3
- Repeat ABG at 4-6 hours if initial improvement is minimal 1, 5, 3
- Early improvement in PaO₂, pH, and PaCO₂ (evident at 1 hour, certainly by 4-6 hours) indicates treatment success 1
- Lack of progress toward correction by 4-6 hours is associated with NIV failure and should prompt consideration of intubation 1, 3
Common Pitfalls to Avoid
Technical Issues Leading to Failure:
- Excessive leakage: Check mask fit; if using nasal mask with persistent leaks, switch to full-face mask or add chin strap 1
- Re-breathing: Ensure expiratory valve patency; consider increasing EPAP if using bi-level support 1
- Patient-ventilator asynchrony: Observe chest expansion, adjust inspiratory/expiratory triggers if available, and ensure adequate EPAP in COPD patients to offset intrinsic PEEP 1
- Inadequate ventilation: Increase target pressure (IPAP), increase inspiratory time, or increase respiratory rate to boost minute ventilation 1
Clinical Pitfalls:
- Excessive oxygen therapy in COPD: Maintain SpO₂ target of 88-92% to avoid worsening hypercapnia 1, 2
- Delayed escalation to invasive ventilation: If persistent or deteriorating acidosis occurs despite optimized NIV settings at 4-6 hours, proceed to intubation 2, 3
- Using NIV in inappropriate settings: Patients with severe acidosis or those who would be intubation candidates if NIV fails should only receive NIV in HDU or ICU settings 1, 3
Equipment Requirements
A single model of ventilator should be used in any clinical area for ease of training and staff familiarity. 1 Essential features for acute NIV include: