Non-Invasive Positive Pressure

Non-Invasive Positive Pressure

Non-invasive positive pressure ventilation (NPPV) is the application of mechanical breaths without airway invasion and is delivered by a nasal or face mask. BiPAP delivers continuous positive airway pressure with different levels of inspiratory and expiratory support. NPPV has been a major advance in the management of acute respiratory distress. There are numerous randomized trials that demonstrate that NPPV lowers intubation rate, mortality, and hospital stay.^17–24 Most recent studies suggest NPPV should be considered first-line therapy for patients with acute hypercapnic and hypoxemic insufficiency.^25–29 A randomized controlled trial performed by Brochard et al compared 85 COPD patients and found the endotracheal intubation rate was 74% for controls receiving standard medical treatment compared to only 26% in the NPPV group.¹⁸ Despite the demonstrated advantages of NPPV, there are scenarios where the inappropriate application of NPPV may be harmful,³⁰ and intubation is the only appropriate approach to managing the patient’s respiratory failure.

There are both good and poor candidates for NPPV (Table 1). Merlani et al published a retrospective study of 104 patients which found that NPPV failures had the following shared characteristics:³¹

• A Glasgow Coma Scale score < 13 at ED admission
• A pH ≤ 7.35 after 1 hour on NPPV
• A respiratory rate ≥ 20 bpm after 1 hour on NPPV

Confalonieri et al analyzed prospective data collected from 1033 patients with COPD exacerbation and found the following variables to predict the risk of failure > 70% on admission:³²

• A Glasgow Coma Score < 11
• A pH < 7.25
• A respiratory rate ≥ 30 bpm

The risk increased to > 90% failure rate if a pH < 7.25 persisted after 2 hours on NPPV.

Evidence from prospective studies of over 500 patients demonstrates that early failed response to NPPV is highly predictive for invasive airway management and mechanical intervention.^31–37

Ultimately, the decision to intubate is a clinical one. While data is important in directing decision making, clinical acumen or ‘gut instinct’ is probably the best guide in making this decision. There is no clinical study or evidence that suggests any single value for arterial pCO₂, pH, or PaO₂ by itself signifies an indication for mechanical ventilation. Clinical assessment of patient muscle fatigue, mental status, and stability relative to their entire emergent presentation should direct care.