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.