Hypercapnic acidosis is protective in an in vivo model of ventilator-induced lung injury

To investigate whether hypercapnic acidosis protects against ventilator-induced lung injury (VILI) in vivo, we subjected 12 anesthetized, paralyzed rabbits to high tidal volume ventilation (25 cc/kg) at 32 breaths per minute and zero positive end-expiratory pressure for 4 hours. Each rabbit was randomized to receive either an FICO2 to achieve eucapnia (Pa-CO2 similar to 40 mm Hg; n = 6) or hypercapnic acidosis (Pa-CO2 80-100 mm Hg; n = 6). Injury was assessed by measuring differences between the two groups' respiratory mechanics, gas exchange, wet:dry weight, bronchoalveolar lavage fluid protein concentration and cell count, and injury score. The eucapnic group showed significantly higher plateau pressures (27.0 +/- 2.5 versus 20.9 +/- 3.0; p = 0.016), change in Pa-O2 (165.2 +/- 19.4 versus 77.3 +/- 87.9 mm Hg; p = 0.02), wet:dry weight (9.7 +/- 2.3 versus 6.6 +/- 1.8; p = 0.04), bronchoalveolar lavage protein concentration (1,350 +/- 228 versus 656 +/- 511 mug/ml; p = 0.03), cell count (6.86 x 10(5) +/- 0.18 x 10(5) versus 2.84 x 10(5) +/- 0.28 x 10(5) nucleated cells/ml; p = 0.021), and injury score (7.0 +/- 3.3 versus 0.7 +/- 0.9; p < 0.0001). We conclude that hypercapnic acidosis is protective against VILI in this model.