Ventilation with high tidal volume induces inflammatory lung injury

Abstract Mechanical ventilation with high tidal volumes (V T ) has been shownto induce lung injury. We examined the hypothesis that this procedureinduces lung injury with inflammatory features. Anesthetized maleWistar rats were randomized into three groups: group 1 (N = 12): V T = 7 ml/kg, respiratory rate (RR) = 50 breaths/min; group 2 (N = 10): V T = 21 ml/kg, RR = 16 breaths/min; group 3 (N = 11): V T = 42 ml/kg, RR= 8 breaths/min. The animals were ventilated with fraction of inspiredoxygen of 1 and positive end-expiratory pressure of 2 cmH 2 O. After 4h of ventilation, group 3, compared to groups 1 and 2, had lower PaO 2 [280 (range 73-458) vs 517 (range 307-596), and 547 mmHg (range330-662), respectively, P<0.05], higher wet lung weight [3.62 ± 0.91vs 1.69 ± 0.48 and 1.44 ± 0.20 g, respectively, P<0.05], and higher wetlung weight/dry lung weight ratio [18.14 (range 11.55-26.31) vs 7.80(range 4.79-12.18), and 6.34 (range 5.92-7.04), respectively, P<0.05].Total cell and neutrophil counts were higher in group 3 compared togroups 1 and 2 (P<0.05), as were baseline TNF- α concentrations [134(range <10-386) vs 16 (range <10-24), and 17 pg/ml (range <10-23),respectively, P<0.05]. Serum TNF-α concentrations reached a higherlevel in group 3, but without statistical significance. These resultssuggest that mechanical ventilation with high V