To accomplish this task, fluid in the filter reservoir of the outgoing tubing of ventilators can be analyzed for sodium and chloride levels compared to controls without pulmonary edema and corrected for dilution/evaporation by calculating the ratio to a reference molecule like urea: if the chloride levels are increased, a predominant hyperactivation of CFTR is likely involved and if levels are found to be reduced, a reduction of CFTR function is likely. This evidence concerns the gene CFTR and pulmonary edema.