Effect of inspired oxygen fraction on alveolar derecruitment in acute respiratory distress syndrome
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High fractions of inspired oxygen (FIO2) used in acute lung injury (ALI) may promote resorption atelectasis. The impact of derecruitment related to high FIO2 in ALI is debated. We evaluated derecruitment with 100% vs. 60% FIO2 at two levels of positive end-expiratory pressure (PEEP).
Fourteen consecutive patients with ALI were studied.
Recruited volume at two PEEP levels was computed from two pressure-volume curves, recorded from PEEP and from zero end-expiratory pressure, using the sinusoidal flow modulation method. PEEP-induced recruitment was measured during prolonged expiration as the difference between the two curves at a given pressure. PaO2/FIO2 was also measured. PEEP was 5 ± 1 or 14 ± 3 cmH2O and FIO2 was 60% or 100%, yielding four combinations. We looked for differences between the beginning and end of a 30-min period with each combination.
Measurement and results
With low PEEP and 100% FIO2, recruited volume decreased significantly from 68 ± 53 to 39 ± 43 ml and PaO2/FIO2 from 196 ± 104 to 153 ± 83 mmHg. With the three other combinations (low PEEP and 60% FIO2 or high PEEP and 60% or 100% FIO2) none of the parameters decreased significantly.
In mechanically ventilated patients with ALI the breathing of pure oxygen leads to derecruitment, which is prevented by high PEEP.