Group assignment of microarray chips.

All microarray chips were assigned, depending on the model of lung injury, to either of two comparisons: One-hit vs. Two-hit models of VILI. Microarray chips included in the meta-analysis (see Table 1) were classified according to the treatment strategies used to induce lung injury. For each comparison we determined the chips that would serve as either control or treatment based on the research question of interest. Non-ventilated (NV), mechanical ventilation (MV), high tidal volume (HV), low tidal volume (LV), lipopolysaccharide (LPS), and acid aspiration (AA).