Effect of PEEP on inspiratory resistance components in patients with acute respiratory distress syndrome ventilated at low tidal volume

OBJECTIVE: To describe the behavior of inspiratory resistance components when positive end-expiratory pressure (PEEP) increases in patients with acute respiratory distress syndrome under a protective ventilation strategy. METHODS: In volume-controlled mode, at 6mL/kg and constant flow, end-inspiratory occlusions were performed at 0, 5 10, 15 and 20cmH(2)O PEEP. Peak, initial and plateau pressure values were assessed, calculating the maximum, minimum and differential resistances. The results were compared by repeated measures analysis of variance (ANOVA) with post hoc Bonferroni correction, considering p < 0.05 significant. RESULTS: The highest maximum resistance was observed at the lowest PEEP levels. The values for 10 and 15cmH(2)O PEEP significantly differed from those for 5 and 0cmH(2)O PEEP, whereas that for 20cmH(2)O PEEP only significantly differed from that for 0cmH(2)O PEEP (p < 0.05). The minimum resistance behaved similarly to the maximum resistance; the values for PEEP levels from 10cmH(2)O to 20cmH(2)O significantly differed from those for 0 and 5cmH(2)O PEEP (p < 0.05). Differential resistance showed the opposite variation to the maximum and minimum resistances. The only PEEP level that showed significant differences from 0 and 5cmH(2)O PEEP was 20cmH(2)O PEEP. Significant differences were also found between 15 and 5cmH(2)O PEEP (p < 0.05). CONCLUSIONS: During protective ventilation in patients with acute respiratory distress syndrome, the maximum resistance of the respiratory system decreases with PEEP, reflecting the minimum resistance response, whereas differential resistance increases with PEEP.