Assessment of the inflammatory effect of low-dose oxygen in mechanically ventilated patients

Purpose Although low doses of oxygen ($ FiO_{2} $ <0.50) are considered nontoxic, recent studies have shown that even lower doses increase pulmonary inflammatory mediators. We aimed to evaluate the acute effects of reducing $ FiO_{2} $ on pulmonary inflammation in mechanically ventilated patients...
Ausführliche Beschreibung

Purpose Although low doses of oxygen ($ FiO_{2} $ <0.50) are considered nontoxic, recent studies have shown that even lower doses increase pulmonary inflammatory mediators. We aimed to evaluate the acute effects of reducing $ FiO_{2} $ on pulmonary inflammation in mechanically ventilated patients without respiratory failure. Methods This study was a prospective, single-center crossover study in a medical/surgical intensive care unit at a university hospital. Hemodynamically stable patients under mechanical ventilation for >24 h without severe respiratory failure ($ PaO_{2} $/$ FiO_{2} $ >250). A basal $ FiO_{2} $ of 0.40 was reduced to 0.21 provided $ SpO_{2} $ remained higher than 90 %. Patients who could not tolerate the reduction in $ FiO_{2} $ to 0.21 were excluded. Results We screened 40 patients, but only 28 (70 %) tolerated $ FiO_{2} $ 0.21. We measured common clinical variables and inflammatory mediators in plasma and in exhaled breath condensate (EBC) at the end of three 4-h periods: (1) basal ($ FiO_{2} $ 0.40), (2) after $ FiO_{2} $ reduction to 0.21, and (3) after returning $ FiO_{2} $ 0.40. We used one-way ANOVA for repeated measurements with $ FiO_{2} $ as the grouping variable. Median values of inflammatory mediators in EBC showed nonsignificant changes among the three periods: $ NO_{2} $ + $ NO_{3} $ 17.1, 14.1 and 11.0 μmol/L (p = 0.2), and 8-isoprostane 4.4, 8.2 and 5.3 pg/ml (p = 0.6) for the three periods, respectively. Plasma levels also showed nonsignificant changes during the period of the study: $ NO_{2} $ + $ NO_{3} $ 12.6, 16.3 and 15.0 μmol/L (p = 0.9), TNFα 13.5, 18.0 and 14.5 pg/ml (p = 0.8), IL-4 12.9, 18.7 and 23.9 pg/ml (p = 0.1), IL-6 50.9, 35.1 and 28.3 pg/ml (p = 0.6), and IL-10 15.2, 22.2 and 22.2 pg/ml (p = 0.7) for the three periods, respectively. Conclusion $ FiO_{2} $ 0.40 in mechanically ventilated patients without severe respiratory failure did not increase systemic or pulmonary inflammation. Ausführliche Beschreibung