Strong Indications for Non-Invasive Ventilation (NIV)
The ATS/ERS 2017 guidelines provide strong recommendations for NIV in two primary clinical scenarios: COPD exacerbations with acute respiratory acidosis (pH ≤7.35), and as an alternative to immediate intubation in patients with severe acidosis who are not immediately deteriorating. 1
Primary Strong Indications
COPD Exacerbation with Acute Respiratory Acidosis
Bilevel NIV is strongly recommended for patients with acute respiratory failure leading to acute or acute-on-chronic respiratory acidosis (pH ≤7.35) due to COPD exacerbation. 1 This represents a strong recommendation with high certainty of evidence based on demonstrated mortality reduction (RR 0.63,95% CI 0.46–0.87) and decreased intubation rates (RR 0.41,95% CI 0.33–0.52). 1
The strongest evidence base exists for patients with pH 7.25–7.35, where NIV reduces:
- Dyspnea sensation 1
- Need for immediate intubation 1
- ICU and hospital length of stay 1
- Mortality 1
- Both respiratory and nonrespiratory infectious complications 1
Response to NIV is typically seen within the first 1–4 hours after initiation, with improvement in pH, respiratory rate, or both serving as good predictors of successful outcome. 1
NIV as Alternative to Immediate Intubation
A trial of bilevel NIV is strongly recommended in patients considered to require endotracheal intubation and mechanical ventilation, unless the patient is immediately deteriorating. 1 This represents a strong recommendation with moderate certainty of evidence. 1
This applies to patients with severe acidosis (mean pH 7.20 in supporting studies) who would otherwise require invasive ventilation. 1 Important exclusions include:
- Respiratory arrest 1
- Apneic episodes 1
- Psychomotor agitation requiring sedation 1
- Heart rate <60 beats/min 1
- Systolic arterial pressure <80 mmHg 1
When NIV is successful in this population, advantages include shorter ICU and hospital stays, fewer complications, reduced need for supplemental oxygen, and fewer hospital readmissions. 1
Additional Strong Indications from Guidelines
NIV is indicated in acute or acute-on-chronic hypercapnic respiratory failure due to chest wall deformity or neuromuscular disease. 1 This carries a Grade C recommendation. 1
CPAP (not NIV) has been shown effective in patients with cardiogenic pulmonary edema who remain hypoxic despite maximal medical treatment, with NIV reserved for patients in whom CPAP is unsuccessful. 1
Critical Implementation Points
Arterial Blood Gas Criteria
Arterial blood gas measurement is critical to NIV application, as the strongest indications are predicated on documented respiratory acidosis (pH <7.35). 1 Blood gases should be measured in most patients with acute breathlessness and repeated after initial medical treatment to determine if NIV remains indicated. 1
Monitoring for Success or Failure
Arterial blood gases should be reassessed after 1-2 hours of NIV to evaluate response. 2 Lack of improvement in pH, PCO2, and respiratory rate after 4-6 hours despite optimal settings indicates likely NIV failure and necessitates consideration of invasive mechanical ventilation. 2
Interface Selection
A full-face mask should be used initially in the acute setting, with transition to a nasal mask after 24 hours as the patient improves. 1
Important Contraindication
NIV should NOT be used routinely in patients with hypercapnia who are not acidotic (pH >7.35) in the setting of a COPD exacerbation. 1 This is a conditional recommendation against NIV based on lack of consistent benefit and potential for harm. 1 The main focus in hypercapnic COPD patients without acidosis should be medical therapy and controlled oxygen therapy targeted to saturation of 88–92%. 1
Common Pitfalls
Hypercapnic coma is not an absolute contraindication to NIV – large case series have shown no difference in outcome between patients with and without hypercapnic coma. 2
Do not delay NIV initiation in patients with acute respiratory acidosis, as early intervention improves outcomes. 2
Avoid excessive oxygen therapy in COPD patients, which can worsen hypercapnia; target oxygen saturation to 88-92%. 2
Do not miss the opportunity for early intubation if NIV is failing, as delayed intubation can worsen outcomes. 2