The radiographic detection of acute pulmonary oedema. A comparison of radiographic appearances, densitometry and lung water in dogs

Abstract

We have induced acute pulmonary oedema in upright anaesthetized dogs by increasing pulmonary microvascular permeability or by extracellular fluid volume overload in order to determine the sensitivity and specificity of the radiograph to the presence of abnormal lung water. Radiographs were taken before and after development of oedema. At the end of the experiment we removed the inflated lungs and froze them in liquid nitrogen and subsequently examined them macroscopically in the frozen state. The extravascular water/dry lung weight ratio was measured gravimetrically on seven portions of each lung. Finally without the base-line films for comparison. We directly measured the change in opacity of the films with a radiographic densitometer. When a dog's mean extravascular water/g dry lung was increased by more than 35% it was invariably recognized, in one or more zones, as definite oedema. Control dogs were reliably recognized as normal when base-line films were used but the distinction between normal and minor degrees of oedema could not be made without the base-line films. There was a positive correlation between radiological grade and lung water, but a great deal of overlap between grades. Densitometry was not a sensitive or reliable method for diagnosing or quantifying oedema. Oedema was usually associated with a decrease in volume of the lower lung zones.