Protective Effects of Hypercapnic Acidosis on Ventilator-induced Lung Injury

To investigate whether respiratory acidosis modulates ventilator-induced lung injury (VILI), we perfused (constant flow) 21 isolated sets of normal rabbit lungs, ventilated them for 20 min (pressure controlled ventilation [PCV] = 15 cm H2O) (Baseline) with an inspired CO2 fraction adjusted for the partial pressure of CO2 in the perfusate (Pco 2 ≅ 40 mm Hg), and then randomized them into three groups. Group A (control: n = 7) was ventilated with PCV = 15 cm H2O for three consecutive 20-min periods (T1, T2, T3). In Group B (high PCV / normocapnia; n = 7), PCV was given at 20 (T1), 25 (T2), and 30 (T3) cm H2O. The targeted Pco 2 was 40 mm Hg in Groups A and B. Group C (high PCV / hypercapnia; n = 7) was ventilated in the same way as Group B, but the targeted Pco 2 was ≅ 70 to 100 mm Hg. The changes (from Baseline to T3) in weight gain ( Δ WG: g) and in the ultrafiltration coefficient ( ΔK f = gr / min / cm H2O / 100g) and the protein and hemoglobin concentrations in bronchoalveolar lavage fluid (BALF) were u...