What are the guidelines for starting Non-Invasive Ventilation (NIV) in a patient with type 2 respiratory failure?

Starting NIV in Type 2 Respiratory Failure

NIV should be initiated when pH <7.35 and PaCO₂ ≥6.5 kPa persist after one hour of optimal medical therapy including controlled oxygen (targeting SpO₂ 88-92%), with respiratory rate >23 breaths/min. 1

Initial Assessment and Optimization Period

Before starting NIV, provide optimal medical therapy for at least 60 minutes, as approximately 20% of acute hypercapnic respiratory failure cases will resolve with medical management alone 1:

• Target oxygen saturation of 88-92% using controlled oxygen therapy to avoid worsening hypercapnia 1
• Administer bronchodilators, corticosteroids, and antibiotics as indicated for the underlying cause 1
• Obtain arterial blood gas (ABG) measurement to confirm respiratory acidosis and quantify severity 1
• Obtain chest X-ray unless severe acidosis (pH <7.25) is present, in which case NIV should not be delayed 1

Specific Thresholds for NIV Initiation

Primary Indication (Grade A Evidence)

For PaCO₂ ≥6.5 kPa: Start NIV when all three criteria persist after optimal medical therapy 1:

• pH <7.35
• PaCO₂ ≥6.5 kPa (49 mmHg)
• Respiratory rate >23 breaths/min

Secondary Consideration (Grade D Evidence)

For PaCO₂ 6.0-6.5 kPa: Consider NIV on a case-by-case basis, as this range is unlikely to contribute significantly to acidosis 1. The guideline development group recommends continued optimal medical care with repeat ABG measurement before committing to NIV in this intermediate range 1.

Severe Acidosis

For pH <7.25: NIV should still be attempted before intubation unless the patient requires immediate intubation 2, 3. Severe acidosis alone does not preclude a trial of NIV, but requires management in an area with immediate access to intubation capability 1.

Initial Ventilator Settings

Start with bi-level pressure support ventilation 4:

• IPAP: 10-15 cmH₂O 4
• EPAP: 4-5 cmH₂O 4
• Use a full-face mask initially in the acute setting 5
• Titrate supplemental oxygen to maintain SpO₂ 88-92% 1

Location of Care Based on Severity

The location should be determined by pH and clinical stability 1, 4:

• pH <7.25 or high risk of deterioration: ICU or HDU with immediate intubation capability 4
• pH 7.25-7.35 with stable presentation: Respiratory ward acceptable if appropriate nursing ratios and monitoring are available 4
• All locations must have staff experienced in NIV and structures for rapid escalation 1

Critical Monitoring Protocol

Immediate Assessment (1-2 hours)

Obtain repeat ABG at 1-2 hours after initiating NIV 1, 4:

• If pH and PaCO₂ are improving: Continue NIV with close monitoring
• If no improvement or deterioration: Reassess ventilator settings and patient tolerance

Secondary Assessment (4-6 hours)

If there has been no improvement in PaCO₂ and pH after 4-6 hours despite optimal ventilator settings, discontinue NIV and proceed to invasive mechanical ventilation 1. Continued use of NIV when the patient is deteriorating increases mortality 1.

Continuous Monitoring

• Oxygen saturation continuously for at least 24 hours 1
• Clinical assessment including respiratory rate, heart rate, accessory muscle use, and coordination with ventilator 1
• Patients showing benefit should receive NIV for as much time as possible during the first 24 hours 1

Contraindications to NIV

Absolute contraindications 1:

• Recent facial or upper airway surgery
• Fixed upper airway obstruction
• Active vomiting
• Inability to protect airway
• Respiratory arrest

Relative contraindications requiring contingency planning for intubation 1:

• Recent upper gastrointestinal surgery
• Copious respiratory secretions
• Severe confusion/agitation
• Life-threatening hypoxemia
• Pneumothorax (insert chest drain first in most cases) 1

Common Pitfalls

Delayed escalation to invasive ventilation is the main risk of NIV, which increases mortality 4. The expansion of ward-based NIV provision may lead to greater delay in expert review and escalation to invasive mechanical ventilation 1.

Using NIV in patients with predominantly metabolic acidosis should be avoided, as the updated guidelines specifically raised the PaCO₂ threshold to 6.5 kPa to limit inappropriate use in mixed acidosis 1.

Inadequate initial medical optimization leads to unnecessary NIV use, as 20% of patients will improve with controlled oxygen and bronchodilators alone 1.