• non-invasive ventilation

Editor,—We read with interest the review by Cross of the use of non-invasive ventilation (NIV) in the emergency department.¹ We have appraised the evidence concerning the effectiveness of NIV in acute respiratory failure and found further evidence that both supports its use and highlights current controversies.

Although Cross comments on individual studies he does not mention the meta-analysis of trials using NIV in patients with acute respiratory failure.² By combining the data in these trials the results achieve significance. Patients with chronic obstructive pulmonary disease (COPD) treated with NIV had reduced intubation rates with a number needed to treat (NNT) of three and reduced mortality with an NNT of five.

Further to this, the three trials of continuous positive airway pressure (CPAP) for the treatment of left ventricular failure (LVF), quoted by Cross, have been the subject of a systematic review.³ This combined the data and found a significant reduction in intubation rates for those receiving CPAP (NNT=4) and a non-significant trend towards decreased mortality.

There are however issues that have not yet been resolved. The one trial comparing CPAP with bi-level positive airway pressure (BiPAP) in patients with LVF⁴ was terminated early because of a high rate of myocardial infarction in the BiPAP group. The BiPAP group contained more patients with chest pain and known coronary artery disease. They also had higher mean creatinine kinase, and lower mean pH and Pao₂ at enrolment. As Cross reports, these differences between the two groups did not achieve statistical significance, but there was a trend towards worse baseline variables in the BiPAP group. With only 27 patients in this study the possibility of a type 2 error also exists. Further trials are needed to determine the role of BiPAP in the treatment of LVF.

Two of the three studies of CPAP in LVF excluded hypotensive patients. CPAP may increase cardiac output in patients with cardiac failure,⁵ and further study is needed to confirm its safety in these patients.

In our department we treat patients with respiratory distress using CPAP for LVF and BiPAP for exacerbations of COPD. Patients who are unable to cooperate or require immediate intubation are excluded. With the use of fully portable equipment NIV is a simple technique, which has the potential to benefit many emergency department patients, and we welcome the attention drawn to this by the review article.