[Positive end-expiratory pressure and tidal volume titration after recruitment maneuver in a canine model of acute respiratory distress syndrome].

OBJECTIVE: To investigate the mechanisms of alveolar derecruitment and titration of positive end-expiratory pressure (PEEP) and tidal volume (V(T)) after recruitment maneuver (RM) in acute respiratory distress syndrome (ARDS). METHODS: Eighteen dogs with oleic acid induced ARDS were ventilated with volume controlled ventilation [VCV, PEEP 16 cm H2O, V(T) 10 ml/kg, respiratory rate (RR) 30 breaths/min] and the steady state in this mode was defined as baseline (0 min). All animals accepted RM by using pressure controlled ventilation [PEEP 35 cm H2O and peak inspiratory pressure (PIP) 50 cm H2O for 1 min] and then randomly assigned into three groups and ventilated by VCV for 4 h: low V(T) and moderate PEEP group (LVMP group, V(T) 10 ml/kg, PEEP 16 cm H2O, RR 30 breaths/min), low V(T) and low PEEP group (LVLP group, V(T) 10 ml/kg, PEEP 10 cm H2O, RR 30 breaths/min) and moderate V(T) and low PEEP group (MVLP group, V(T) 15 ml/kg, PEEP 10 cm H2O, RR 20 breaths/min). Oxygenation, lung mechanics, hemodynamics and lung injury score were measured. RESULTS: (1) The average lower inflection pressure (LIP) was identified as (16.0 +/- 2.1) cm H2O. (2) PaO(2) in the LVMP group [(371 +/- 64) mm Hg at 30 min and (365 +/- 51) mm Hg at 60 min] was higher than that in the LVLP and the MVLP group [(243 +/- 112), (242 +/- 97) mm Hg at 30 min and (240 +/- 108), (232 +/- 87) mm Hg at 60 min, respectively; all P < 0.05], but no significant differences were observed among three groups from the second hour after RM to the end of the experiment. Better ventilation profiles were observed in the MVLP group. (3) Compared with baseline, marked cardiac compromise with higher airway plateau pressure (Pplat) and lower static respiratory compliance (Cst) were found in the LVMP group, while improvement was observed in other two groups. Cst in the MVLP group was slightly higher than that in the LVLP group. (4) No significant differences of lung injury were found from bronchoalveolar lavage fluid (BALF) analysis. CONCLUSIONS: Higher PEEP close to LIP maybe useful in preventing alveolar recollapse and improving oxygenation, but harmful to hemodynamics and may increase the risk of lung jury. Lower PEEP combined with moderate tidal volume after RM may be a more reasonable approach than conventional lung protective ventilation.