Acute effects of hyperoxemia on dyspnoea and respiratory variables during pressure support ventilation

Objective:To evaluate the acute effect of hyperoxemia on the comfort and the respiratory variables in patients undergoing pressure support ventilation (PSV) for acute respiratory failure (ARF).Design and Setting:Prospective, observational study performed in the intensive care unit of a university hospital.Patients:Thirteen semirecumbent patients were ventilated in PSV mode, the setting of which was established by the treating physician who was blinded to the study. Measurements:The variables measured at different levels (21-80%) of FiO(2) randomly applied were: minute volume (V-E), respiratory frequency (f) and the pressure develing during the first 100 ms of an occluded breath (P-0.1). These variables were firstly measured at the level of FiO(2) chosen by the treating physician. Severity of dyspnea was rated using the visual analogue scale 15' after each FiO(2) variation.Results:Modulation of FiO(2) was able to vary significantly the respiratory variables, since a FiO(2) increase was associated with a decrease in dyspnea, P-0.1, f, and V (E). While valuable variations were detected at both lower and higher values of FiO(2) than those established by the treating physician, a significant improvement in the respiratory variables was detected at FiO(2) 60%. The reduction in respiratory drive was statistically related to an amelioration of dyspnea (R-2 = 0.89) even at values of FiO(2) higher than 60%.Conclusions:During PSV the respiratory drive can be heavily modulated by varying the FiO(2) since even at FiO(2) greater than 0.6 dyspnea and respiratory variables continued to improve.