The Influence of Clinically Undetectable Pulmonary Edema on Small Airway Closure in the Dog

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Abstract
The relationship between elevated pulmonary extravascular water volume (PEWV) and small airway closure was examined. The slow accumulation of lung water was achieved by a combination of pulmonary venous hypertension and mild hemodilution. PEWV was measured using a double indicator method based on the differential right to left transit time for simultaneously injected Evans blue dye and tritiated water. Trapped gas volume (VTG) was measured by the helium equilibration technique. Clinically undetectable levels of pulmonary engorgement and edema were reproducibly associated with an increase in gas trapping. Positive end expiratory pressure reduced, but did not abolish, edema formation. Evaluation of airway closure, with consequent gas trapping and pulmonary shunting, is currently non-invasive, simple and safe. Determination of gas trapping or closing volume should be incorporated into the routine pre-operative evaluation of patients prior to major surgery.