Oxygen tolerance in patients with acute respiratory failure

Objective: To search for a threshold of pulmonary oxygen toxicity in patients with acute respiratory failure. Design: Retrospective study over a 10-year period. Setting: Three intensive care units of two university hospitals. Patients and participants: Seventy-four patients with acute respiratory failure ventilated continuously with a FIO₂ L 0.9 for at least 48 h were selected. Interventions: Information regarding status, scoring, diagnosis and therapeutic interventions upon admission and ICU course were extracted from the patients' charts. Measurements and results: We found that total exposure [mean (standard error of the mean) ] to a FIO₂ of 0.9 (TE 90) or more was 5.6 (1.1) days in the 17 survivors (S) versus 5.9 (0.5) days in the 57 non-survivors (D) (NS). Total exposure time to a FIO₂ more than 0.5 (TE 50) was 16.5 (2.6) days in S and 11.2 (1) days in D (p < 0.05). The PaO₂/FIO₂ ratio became significantly higher in S only 5 days after beginning FIO₂ of 0.9 or more. Hypoxemia was not frequent at the time of death, whereas in 70 % of the non-survivors there were at least three organ failures in the last 48 h. In univariate analysis, the duration of exposure to FIO₂ of 0.9 or more was not different in survivors and non-survivors, and the average total duration of exposure to FIO₂ of more than 0.5 was even longer in survivors. In multivariate analysis, exposure shorter than 10 days to FIO₂ more than 0.5 and exposure longer than 4 days to a FIO₂ of 0.9 or more were significantly associated with death. However, despite a larger exposure to a FIO₂ of 0.9 or more during the last 5 years of the study, the trend moved towards a higher survival rate during this period compared with the first 5 years of the study. Conclusions: Thus, our data provide circumstantial evidence that the lungs of patients with acute respiratory failure might exhibit some relative resistance to prolonged oxygen exposure. Therefore, it might be worthwhile carrying out a prospective study of different FIO₂ strategies in such patients. Received: 14 February 1997 Accepted: 2 March 1998