Quantitative Assessment of Pulmonary Edema

Abstract

The present study has attempted to establish a reliable method for distinguishing quantitatively between pulmonary engorgement and engorgement plus edema. Pulmonary engorgement was produced in intact, anesthetized dogs by inflating a balloon in the left atrium followed by saline hemodilution. Hemodynamic events monitored included left atrial and pulmonary arterial pressures, and the colloid osmotic pressure. Clinical criteria, such as the rate and frequency of breathing, the chest roentgenogram, and the presence of audible rales, failed to distinguish reliably between engorgement and edema. The mechanics of breathing were more severely altered by engorgement and edema than by engorgement alone, but considerable overlap was present. Determination of the pulmonary blood volume and the extravascular water space of the lungs, by means of simultaneous T-1824 and tritiated water dilution curves, as described by Chinard and Enns, was a reliable method of detecting and quantifying pulmonary edema. The water space measured by this technique averaged 3.5 ml/kg body wt in normal, anesthetized dogs. It correlated well with the total lung water content determined at autopsy, measuring a constant fraction (approximately 50%) of the total lung water content, even in the presence of severe pulmonary edema. According to the results of the present study, pulmonary edema could be predicted reliably at autopsy when the extra-vascular water space was 6.0 ml/kg of body wt or greater.