Continuous exhaled breath condensate pH collection and assay system (ALFA monitor, Respiratory Research, Inc., Austin, Texas) consists of a condenser attached to the expiratory limb of the ventilator. Exhaled breath condensate is collected continuously from the expiratory port, condensed in a cooling chamber, CO2 removed, and collected in an inferior chamber where pH is continuously read. This yields a continuous, responsive measure from ventilated patients, which (1) takes samples from an exhaust port on the outside of the ventilator circuit, and (2) adds no measurable resistance to the ventilator circuit. The measurement of EBC in patients with lung injury may serve as an early marker of derecruitment.