The applications of non-invasive ventilation (NIV) include: acute exacerbation of chronic obstructive pulmonary disease (COPD) and cardiogenic pulmonary oedema, for immunocompromised patient, during failure to wean from ventilation. It is essential before NIV is initiated that arterial blood gas measurements be available. The patient should be established upon appropriate oxygen therapy and interpretation must be made in the context of the FiO2. Correct patient selection is essential for the success of NIV: it is a complementary not alternative therapy to IPPV. The successful instigation of NIV is very dependent upon establishing a good rapport with the patient and inspiring confidence in what will feel like a very unusual treatment. The complications of NIV include mild gastric distension, pressure effects of the mask and straps causing facial tissue damage, eye irritation, sinus pain or nasal congestion, and significant haemodynamic effects resulting from NIV that are unusual although hypotension may occur.