Non-Invasive Ventilation

Dr John Griffiths DICM MRCP FRCA MA
CriticalCareUK Editor

Focus on non-invasive positive pressure ventilation

Non-invasive positive pressure ventilation (NPPV) has been used increasingly over the past decade in an effort to both avoid endotracheal intubation and to accelerate weaning from mechanical ventilation. Data from randomised controlled trials support the use of NPPV in acute exacerbations of chronic obstructive pulmonary disease (COPD), respiratory failure in immunosuppressed patients and in patients with cardiogenic pulmonary oedema. However, the efficacy of NPPV in the management of respiratory failure from other causes (e.g. chest trauma) is less clear.

Focus on NPPV in exacerbations of COPD

The largest number of studies investigating NPPV has been conducted in patients with acute exacerbations of COPD. A systematic review and meta-analysis published in the British Medical Journal isolated seven randomised controlled trials (conducted between 1993 and 2002) that compared NPPV plus usual medical care with medical care alone in the management of respiratory failure associated with COPD. All patients enrolled in the trials had hypercapnic respiratory failure (PaCO2 >6 kPa). In the majority of patients, hypercapnic respiratory failure was associated with a pH <7.35. Patients with a primary diagnosis of pneumonia were excluded. All patients had received maximal medical therapy before NPPV was started. However, the medical treatment was not standardised and included inhaled and intravenous β₂ agonists, corticosteroids, aminophylline, doxapram and antibiotics. The trials included in the systematic review also differed widely in their design, including the type of NPPV used. All trials showed treatment benefits with NPPV, and some demonstrated improved survival. The meta-analysis concluded that NPPV significantly reduces mortality (relative risk 0.41, 95% confidence interval 0.26 to 0.64) and reduces the need for endotracheal intubation, the rate of treatment failure, complications and length of hospital stay.

Focus on NPPV in cardiogenic pulmonary oedema

In the treatment of cardiogenic pulmonary oedema, there are several randomised and non-randomised studies investigating continuous positive pressure ventilation (CPAP) or NPPV. Both ventilatory techniques have been shown to lower the rate of intubation and improve oxygenation when compared with standard medical therapy alone. Current evidence supports the use of CPAP over NPPV in the treatment of respiratory failure associated with cardiogenic pulmonary oedema. In one non-controlled study, an unusually high mortality rate was noted in patients with acute myocardial infarction who received NPPV. In the only one randomised controlled trial comparing CPAP and NPPV in the treatment of patients with acute pulmonary oedema, the trial was stopped prematurely because of a greater rate of myocardial infarction in the NPPV group. However, the trial suffered from bias at time of randomisation. Further research is therefore necessary to determine the true efficacy and safety of NPPV in the treatment of patients with acute pulmonary oedema, especially in patients with pulmonary oedema complicated or caused by acute myocardial infarction.

Focus on NPPV in immunosuppressed patients

There is accumulating evidence that early initiation of NPPV in immunosuppressed patients with acute respiratory failure (e.g. organ transplant recipients or patients with haematological malignancies) can reduce both the need for intubation and mortality when compared with medical therapy alone. These findings are especially important given the significant mortality rate (>80%) that is reported in patients with haematological malignancies requiring intubation and mechanical ventilation.
Focus on NPPV in weaning patients from mechanical ventilation
Studies assessing NPPV as a means to facilitate weaning from invasive mechanical ventilation have again concentrated on patients with COPD. In two randomised trials, patients who met criteria for the discontinuation of mechanical ventilation but who had failed trials of spontaneous breathing (e.g. breathing on a T-piece) were subjected to either a conventional weaning plan or elective extubation to NPPV. Patients in the elective extubation to NPPV group had shorter ventilation times and a reduced mortality.

However, a recent study suggests that in a heterogeneous group of patients who have been successfully weaned and extubated, NPPV does not prevent the need for reintubation. In fact, NPPV actually increased mortality, possibly because there was undue delay to reintubation, resulting in prolonged respiratory distress.

Key learning points

• NPPV has an important role in the management of acute respiratory failure. 
• Current evidence supports its use in acute exacerbations of COPD and in acute respiratory failure in immunosuppressed patients. 
• NPPV should not delay intubation and mechanical ventilation in patients where this is necessary. 
• Careful patient selection and early recognition of failure of NPPV is crucial for a positive outcome.

Key references

Lightowler JV, Wedzicha JA, Elliot MW, Ram FSF.
Non-invasive positive pressure ventilation to treat respiratory failure resulting from exacerbations of chronic obstructive pulmonary disease: Cochrane systematic review and meta-analysis.
BMJ 2003; 326: 185-187.

Liesching T, Kwok H, Hill NS.
Acute applications of noninvasive positive pressure ventilation.
Chest 2003; 124: 699-713. 

Rusterholtz T, Kempf J, Berton C et al. 
Noninvasive positive pressure ventilation with face mask in patients with acute cardiogenic pulmonary oedema.
Intensive Care Med 1999; 25: 21-28. 

Mehta S, Jay GD, Woolard RH et al.
Randomized, prospective trial of bilevel versus continuous positive pressure ventilation in acute pulmonary oedema.
Crit Care Med 1997; 25: 620-628. 

Beltrame F, Lucangelo U, Gregori D, Gregoretti C.
Noninvasive positive pressure ventilation in trauma patients with acute respiratory failure.
Monaldi Arch Chest Dis 1999; 54: 109-114. 

Ferrer M, Esquinas A, Arancibia F et al.
Noninvasive ventilation during persistent weaning failure: a randomized controlled trial.
Am J Resp Crit Care Med 2003; 168: 70-76. 

Nava S, Ambrosino N, Clini E et al.
Noninvasive mechanical ventilation in the weaning of patients with respiratory failure due to obstructive pulmonary disease: a randomized, controlled trial.
Ann Intern Med 1998; 128: 721-728. 

Esteban A, Frutos-Vivar F, Ferguson N et al.
Noninvasive positive pressure ventilation for respiratory failure after extubation.
N Engl J Med 2004; 350: 2452-2460.