Effects of short-term oxygenation changes on acute lung injury patients undergoing pressure support ventilation.

We investigated the effects of short-term oxygenation changes upon the neuromuscular respiratory drive (airway occlusion pressure [P0.1]), minute ventilation (VE), and respiratory rate (RR) in 12 acute lung injury patients undergoing pressure support ventilation. We ventilated the patients first at a high level (H1) of oxygenation, then at intermediate (I), at low, and again at the high (H2) level. The H1 and H2 periods showed no differences. In the H1, I, and L periods, PaO2 was 158 +/- 68, 75 +/- 12, and 55 +/- 6 mm Hg, respectively. Decreasing oxygenation caused very significant increases in VE, RR, and P0.1. Differences in RR, VE, and rapid shallow breathing index were significant at step H1 versus I. Changes in P0.1 appeared to be higher when the H1 value was higher than normal. An arterial oxygenation target higher than the generally accepted 60 mm Hg level may decrease both RR and VE.