A topic update outlining practical implementation tips, contraindications and current evidence appears in CMAJ.
Key points of the evidence summary by indication:
COPD exacerbation with respiratory failure---established.
Status asthmaticus---controversial. Some promising early results. Large studies needed.
Acute cardiogenic pulmonary edema (CPAP or NPPV)---established (especially CPAP) in patients without acute myocardial infarction. (Contraindicated if myocardial infarction present).
Miscellaneous forms of respiratory failure including non-cardiogenic hypoxemic respiratory failure and post operative respiratory failure---results appear to vary with setting and etiology of respiratory failure. Promising for some indications.
Selected patients who fail spontaneous breathing trials while intubated (in which extubation followed by NPPV is used as an alternative to continued intubation)---shows great promise and may emerge as a popular strategy given present day concerns about ventilator associated pneumonia and length of ICU stay.
Use in extubated patients, to prevent recurrent respiratory failure and need for reintubation---effective in selected high risk patients.
Use in respiratory failure occurring after extubation---not effective.
Many caveats and precautions apply, which should be read in their entirety in the referenced article.