What is Non-Invasive Ventilation (NIV)?

What is Non-Invasive Ventilation (NIV)?

Non-invasive ventilation (NIV) is a method of delivering positive pressure ventilatory support through a face or nasal mask without requiring endotracheal intubation, primarily used to treat acute hypercapnic respiratory failure and avoid the complications associated with invasive mechanical ventilation. 1

Definition and Mechanism

NIV refers specifically to non-invasive positive pressure ventilation delivered via interface masks rather than through an endotracheal tube. 1 The technique provides ventilatory assistance by:

• Delivering positive pressure during both inspiration (IPAP) and expiration (EPAP) through facial or nasal masks, which augments the patient's own respiratory efforts without requiring an artificial airway 2, 3
• Reducing the work of breathing and improving gas exchange by supporting ventilation while maintaining the patient's natural airway defenses 4

Important distinction: NIV is different from CPAP (continuous positive airway pressure), which delivers constant pressure throughout the respiratory cycle, whereas NIV provides variable pressure support with higher inspiratory and lower expiratory pressures. 1

Primary Clinical Indications

The British Thoracic Society establishes clear evidence-based indications where NIV demonstrates mortality benefit:

Strong Evidence (Grade A)

• COPD exacerbations with respiratory acidosis (pH 7.25-7.35) despite maximal medical therapy, where NIV reduces intubation rates, hospital-acquired pneumonia, ICU length of stay, and mortality 2, 1
• Hypercapnic respiratory failure from chest wall deformity (scoliosis, thoracoplasty) or neuromuscular diseases 1
• Cardiogenic pulmonary edema unresponsive to CPAP alone 1, 5
• Weaning from tracheal intubation, particularly in COPD patients 1, 3

Moderate Evidence

• Immunocompromised patients with respiratory failure 4, 3
• Chest wall trauma with persistent hypoxemia despite adequate analgesia (using CPAP preferentially) 2

Absolute Contraindications

NIV should not be used in the following situations, as these predict failure and delay necessary intubation:

• Impaired consciousness or inability to protect airway 1
• Severe hypoxemia unresponsive to initial therapy 1, 5
• Copious respiratory secretions that cannot be cleared 1

Critical caveat: NIV should never substitute for intubation when invasive ventilation is clearly more appropriate. 1, 2

Initial Setup and Settings

Equipment Requirements

• Full-face mask initially (switching to nasal mask after 24 hours as patient improves), with multiple sizes available 2
• Dedicated NIV ventilator with appropriate monitoring capabilities 1

Starting Parameters

• IPAP: 8-12 cmH₂O 2
• EPAP: 3-5 cmH₂O 2
• FiO₂: Start at 40%, titrating to maintain SpO₂ >92% (or 85-90% specifically in COPD to avoid CO₂ retention) 2

Monitoring for Success or Failure

Early Assessment (1-2 hours)

• Obtain arterial blood gases at 1-2 hours to assess PaO₂, PaCO₂, and pH improvement 2, 5
• Expect clinical improvement by 4-6 hours; lack of progress indicates likely NIV failure requiring intubation 2

Red Flags for Failure

• Deteriorating consciousness level requires immediate intubation consideration 2, 5
• Worsening acidosis or hypercapnia despite optimized NIV 2

Clinical Benefits

When appropriately applied, NIV provides:

• Fewer ICU referrals for intubation 1, 5
• Shorter ICU stays 1, 5
• Reduced mortality in acute respiratory failure 1, 5
• Elimination of endotracheal tube-related complications, including ventilator-associated pneumonia 4

Critical Pitfalls to Avoid

• Do not give excessive oxygen in COPD patients—target SpO₂ 85-90% to prevent worsening hypercapnia 2
• Do not delay intubation in patients failing NIV trial; this increases mortality 2, 3
• Do not use NIV outside appropriate monitoring settings (respiratory ward, HDU, or ICU with ICU backup available) 1