Confalonieri and colleagues raise the issue of appropriate selection guidelines for the use of noninvasive positive pressure ventilation in patients with acute respiratory failure. They correctly point out that "hemodynamic instability" was not precisely defined in our review, and they report their experience with a series of patients, including some with hypotension, most of whom were successfully treated with noninvasive positive pressure ventilation. Information on the appropriate use of noninvasive positive pressure ventilation in patients with acute respiratory failure is evolving, and it is not possible to delineate precise patient selection criteria because of the lack of well-designed scientific studies in the literature. The selection guidelines that we presented in our article were culled from currently available studies and our own experience, but it is important to emphasize that they are only guidelines and that clinical judgment must always be exercised when they are applied in individual patients.

Confalonieri and colleagues also failed to precisely define hemodynamic instability, and their definition of hypotension (systolic blood pressure <100 mm Hg) is fairly lenient. We agree that the patients described by Confalonieri and associates appear to have been appropriately selected as candidates for noninvasive positive pressure ventilation, and the success rate of approximately 66% compares favorably with those of other similar series. We maintain, however, that some patients with "hemodynamic instability" remain poor candidates for this treatment. These include patients with not only hypotension but also with evidence of inadequate organ perfusion not easily reversed by fluid resuscitation or pressor agents. In such patients, intubation and paralysis may be necessary to minimize the energy consumption by respiratory muscles, and application of noninvasive positive pressure ventilation could be deleterious by delaying the use of more definitive therapeutic measures.