• François Bouvet, Didier Dreyfuss, Rachida Lebtahi, Geneviève Martet, Dominique Le Guludec, and Georges Saumon.
• IFR Claude Bernard, Faculté Xavier Bichat, Paris, France.
• Crit. Care Med. 2005 Jan 1;33(1):155-60; discussion 250-2.

ObjectiveTo evaluate whether hypercapnic acidosis attenuates acute alterations of pulmonary capillary permeability due to high lung stretch in rats using a simple, noninvasive, scintigraphic method.DesignProspective, randomized, controlled animal study.SettingUniversity research laboratory.SubjectsMale adult Wistar rats weighing 291 +/- 7.5 g.InterventionsThree groups of rats were studied: controls ventilated with a low (6 mL/kg body weight) tidal volume and rats ventilated with a high (38 mL/kg body weight) tidal volume under normocapnic (Paco(2) = 35.2 +/- 1.65 mm Hg) or hypercapnic (Paco(2) = 102.5 +/- 5.63 mm Hg) conditions.Measurements And Main ResultsPulmonary capillary permeability alterations were assessed by monitoring the rate of (111)In-transferrin accumulation in lung tissue. Respiratory system pressure-volume curves were registered and analyzed. High tidal volume ventilation increased In-transferrin plasma to lung flux in such a way that I(111)In-transferrin behaved like a marker of water. The rate of initial (first 30 mins of high tidal volume ventilation) lung transferrin accumulation measured by scintigraphy (standardized lung/heart ratio) was steady, correlated with the percent decrease in respiratory system compliance (a marker of edema progression), and did not differ between normocapnic and hypercapnic groups (18.9 +/- 3.97 vs. 14.2 +/- 2.89%/hr, not significant). However, lung In-tranferrin accumulation rate was highly scattered due to variable interindividual mechanical properties of the respiratory system. This rate was correlated with initial values of volume of the upper inflection point of the pressure-volume curve (r = -.53, p < .001) and end-inspiratory pressure (r = .54, p < .001). Mechanical properties were similar in normocapnic and hypercapnic rats. There was no difference between In-transferrin accumulation rates in these rats when a stringent selection was made based on end-inspiratory pressure (28-32 cm H(2)O) or body weight (330-360 g).ConclusionsHypercapnic acidosis does not influence in vivo the acute increase in pulmonary capillary permeability due to high-volume ventilation.

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