Acute exacerbation of COPD. Several randomized controlled trials (RCT) and meta-analyses have assessed the potential benefits of NPPV in patients with acute exacerbations of COPD. In COPD, NPPV improves gas exchange and facilitates respiratory muscle rest to decrease the work of breathing, which allows for respiratory recovery and time to effectiveness of standard therapies.5 Multiple trials have demonstrated that the addition of NPPV to usual care decreases intubation and mortality rates, as well as hospital lengths of stay (LOS).5-8
A Cochrane review of eight RCTs comparing NPPV with usual care noted a greater than 50% reduction in risk of intubation, and a number needed to treat (NNT) of eight patients to prevent one death.5 Quon and colleagues also compared NPPV to usual care in a meta-analysis of 14 trials.6 Eleven of these trials evaluated hospital mortality, which was decreased by 55% in patients receiving NPPV. Twelve trials assessed need for intubation, which decreased by 65%. In these trials, BiPAP was the most commonly used modality (see Table 3, for a comparison of NPPV modalities). Study patients had an average pH of 7.31 with an average PaCO2 of 68 mmHg. It was noted that the beneficial effects of NPPV increased as pH decreased. An earlier meta-analysis from Keenan and colleagues supported this notion, noting that the subgroup of patients with pH <7.3 benefited most in terms of decreased rates of intubation, hospital LOS, and hospital mortality.7 In this 2003 study, patients with relatively mild exacerbations of COPD did not benefit from the addition of NPPV to usual care. Based on the amount of positive evidence, NPPV is recommended in patients experiencing severe exacerbations of COPD as evidenced by a pH <7.35 and relative hypercarbia.1,2,4,7
click for large version
Table 3. Comparison of NPPV modalities
Cardiogenic pulmonary edema. In patients with acute cardiogenic pulmonary edema, NPPV has been found to be beneficial, decreasing mortality, rates of intubation, and hospital LOS. Physiologically, NPPV augments cardiac output, improves respiratory mechanics, and decreases afterload.10 Cardiogenic edema is variably defined and has a number of causes elucidated in an analysis of 11 RCTs conducted by Masip and colleagues. These causes included acute coronary syndrome (31%), hypertension (27%), congestive heart failure (14%), and a combination of respiratory infection, arrhythmia, volume overload, and treatment noncompliance (28%).9 In this analysis, CPAP and BiPAP demonstrated a combined 43% reduction in mortality and a 57% reduction in intubation. More recently, Peter and colleagues described a statistically significant reduction in hospital mortality and the need for intubation with CPAP, while BiPAP only demonstrated a statistically significant decrease in need for intubation.10 Thus, there appears to be some evidence that CPAP is the preferred NPPV mode in patients with acute cardiogenic pulmonary edema. Despite inclusion of a recent, large RCT showing no benefit of NPPV versus usual care in cardiogenic pulmonary edema, the overall positive effect of NPPV persisted, particularly when the cause of pulmonary edema was acute coronary syndrome.11
Weaning after intubation. NPPV has been evaluated as a method to facilitate early extubation, as a measure to prevent extubation failure, and as a treatment modality for respiratory failure following extubation, with mixed results.12,13 In 1998, a small trial compared the use of NPPV in COPD patients to facilitate early extubation with a standard weaning protocol. In this population, early NPPV resulted in better weaning rates with shorter times of mechanical ventilation (10 vs. 16 days), fewer days in the ICU, and improved 60-day survival rates (92% vs. 72%).3,14 In another RCT not limited to COPD patients, Grault and colleagues found that NPPV reduced the duration of intubation (4.5 vs. 7.6 days) but was not associated with benefits in ICU length of stay or survival previously described.3,15 Thus, though NPPV may be beneficial in facilitating early extubation in COPD patients, it is not recommended in other patient populations.4