Protective Effects of Hypercapnic Acidosis on Ventilator-induced Lung Injury

TLDR

The study investigates whether respiratory acidosis modulates ventilator‑induced lung injury in isolated rabbit lungs. Twenty‑one isolated rabbit lungs were ventilated at baseline and then assigned to control, high‑pressure normocapnic, or high‑pressure hypercapnic groups, with injury assessed by weight gain, ultrafiltration coefficient, and bronchoalveolar lavage protein and hemoglobin. High‑pressure ventilation without hypercapnia caused significantly greater weight gain, ultrafiltration, and BALF protein/hemoglobin than either control or hypercapnic ventilation, indicating that hypercapnia mitigates VILI. The authors conclude that respiratory acidosis decreases VILI severity in this rabbit model.

Abstract

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 used to assess injury. Group B experienced a significantly greater Δ WG (14.85 ± 5.49 [mean ± SEM] g) and ΔK f (1.40 ± 0.49 g / min / cm H2O / 100 g) than did either Group A ( Δ WG = 0.70 ± 0.43; ΔK f = 0.01 ± 0.03) or Group C ( Δ WG = 5.27 ± 2.03 g; ΔK f = 0.25 ± 0.12 g / min / cm H2O / 100 g). BALF protein and hemoglobin concentrations (g / L) were higher in Group B (11.98 ± 3.78 g / L and 1.82 ± 0.40 g / L, respectively) than in Group A (2.92 ± 0.75 g / L and 0.38 ± 0.15 g / L) or Group C (5.71 ± 1.88 g / L and 1.19 ± 0.32 g / L). We conclude that respiratory acidosis decreases the severity of VILI in this model.Keywords: respiratory acidosis; hypercapnia; mechanical ventilation; acute lung injury; rabbits