LJ Hernan, S Penfil, BP Fuhrman, MS Dowhy, MC Papo, CL Leach

Perfluorocarbon-associated gas exchange or partial liquid ventilation (gas ventilation of the liquid-filled lung) supports gas exchange in patients with lung disease. Perflubron, a perfluorocarbon suitable for the gas exchange process, can carry 50 ml O₂ per 100 ml while an equal volume of gas has twice that capacity. Owing to this limited solubility, uptake of O₂ by blood reduces alveolar pO₂ more during gas exchange than during gas ventilation. The alveolar gas equation overestimates alveolar pO₂ and calculations using this variable during perfluorocarbon-associated gas exchange. Functional FiO₂ is the theoretical FiO₂ predicted by the alveolar gas equation to yield the pO₂ measured in tracheal perflubron during this gas exchange. We hypothesize there exists a consistent relationship between the FiO₂ during gas exchange and the functional FiO₂. Ten piglets had perflubron (30 ml/kg) instilled into the trachea. FiO₂ was randomly varied between 0.45 and 1.0. At each FiO₂, alveolar pO₂ was estimated using the alveolar gas equation and by directly measuring the pO₂ of perflubron. An equation was derived to describe the relationship between FiO₂ during gas exchange and functional FiO₂. Functional FiO₂= 0.72* (FiO₂ during perfluorocarbon-associated gas exchange) + 0.059. At a full liquid functional residual capacity, functional FiO₂ predicts the pO₂ of perflubron and will be a more accurate measurement of alveolar PO₂.