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

Abstract

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 FiO2 randomly applied were: minute volume (VE), respiratory frequency (f) and the pressure develing during the first 100 ms of an occluded breath (P0.1). These variables were firstly measured at the level of FiO2 chosen by the treating physician. Severity of dyspnea was rated using the visual analogue scale 15′ after each FiO 2 variation. Results: Modulation of FiO2 was able to vary significantly the respiratory variables, since a FiO2 increase was associated with a decrease in dyspnea, P0.1, f, and VE. While valuable variations were detected at both lower and higher values of FiO2 than those established by the treating physician, a significant improvement in the respiratory variables was detected at FiO2 60%. The reduction in respiratory drive was statistically related to an amelioration of dyspnea (R2 = 0.89) even at values of FiO2 higher than 60%. Conclusions: During PSV the respiratory drive can be heavily modulated by varying the FiO2 since even at FiO2 greater than 0.6 dyspnea and respiratory variables continued to improve. © Springer-Verlag 2005.