Pure hypoxemic patients admitted to intensive care unit in a teaching hospital have been randomized to be treated by conventional ventilatory support or non-positive mechanical ventilation support. Those patients who did not benefit from the experimental non-positive ventilatory support, were intubated and conventionally mechanically ventilated and discarded for analysis. The primary outcome was mortality rate in both groups, and secondary outcomes were length of stay, improvement of oxygenation, and reduced complications rates.