Hypercapnic acidosis modulates inflammation, lung mechanics, and edema in the isolated perfused lung☆

Abstract 

Objective

Low tidal volume (V_T) ventilation strategies may be associated with permissive hypercapnia, which has been shown by ex vivo and in vivo studies to have protective effects. We hypothesized that hypercapnic acidosis may be synergistic with low V_T ventilation; therefore, we studied the effects of hypercapnia and V_T on unstimulated and lipopolysaccharide-stimulated isolated perfused lungs.

Materials and Methods

Isolated perfused rat lungs were ventilated for 2 hours with low (7 mL/kg) or moderately high (20 mL/kg) V_T and 5% or 20% CO₂, with lipopolysaccharide or saline added to the perfusate.

Results

Hypercapnia resulted in reduced pulmonary edema, lung stiffness, tumor necrosis factor α (TNF-α) and interleukin 6 (IL-6) in the lavage and perfusate. The moderately high V_T did not cause lung injury but increased lavage IL-6 and perfusate IL-6 as well as TNF-α. Pulmonary edema and respiratory mechanics improved, possibly as a result of a stretch-induced increase in surfactant turnover. Lipopolysaccharide did not induce significant lung injury.

Conclusions

We conclude that hypercapnia exerts a protective effect by modulating inflammation, lung mechanics, and edema. The moderately high V_T used in this study stimulated inflammation but paradoxically improved edema and lung mechanics with an associated increase in surfactant release.

Keywords: Hypercapnic acidosis, Isolated perfused lung, Surfactant