Physiologic bases for the treatment of pulmonary edema

Influence of Airway Pressures on Edema in the Isolated Dog's Lung

The left lower lobe of anesthetized, heparinized dogs was excised, weighed, and cannulated. Another lobe of the same dog was excised for control purposes. The cannulated lobe was perfused by a system of adjustable reservoirs which was fed with fresh blood from a donor dog. The perfused lobe was mounted on an electronic balance so that weight changes could be recorded together with the pressures in the inflow and outflow conduits and in the bronchus. When the per fusion pressures were varied within normal limits, the weight of the lobes reached stable plateaus. Abnormally high perfusion pressures caused a continuous, steady increase in lobe weight, which was evident from the slope of the weight registration. Blood holdup in the lobe was measured by comparing the hemoglobin content of the control lobe with that of the experimental specimen taken at the end of an experiment. Blood holdup accounted for only about 10 per cent of the weight increase of edematous lobes. Initial observations were made in collapsed lobes; in the course of some experiments these lobes were inflated and the static airway pressures were then kept at varying levels.

Irrespective of the perfusion pressures, transudate did not issue from the airway as long as the lobe was collapsed. Abnormal perfusion pressures caused the accumulation of fluid, which continued as long as the perfusion pressures were constant. The rate of transudation was determined by the perfusion pressures and was not influenced by inflation of the collapsed lobe nor by variations of the static airway pressure. When a collapsed lobe had become edematous anti was then inflated, transudate issued from the airway. Increases of the static airway pressure did not decrease the rate of fluid accumulation, but only confined the transudate to the lung and prevented its discharge from the airway.

Therapy of Experimental Pulmonary Edema in the Dog

The results of analysis of edema fluid and excised lungs show that there is leakage of protein-rich fluid into the lung tissue and ultimately into the respiratory passages. This leakage cannot be explained by the reduction in oxygen uptake as observed in lung tissue slices. The ultimate cause of pulmonary edema is not known. The survival time of anesthetized dogs suffering from thermal edema, can be prolonged by inhalation of oxygen and by administration of antihistaminic drugs and pulmonary vasodilators.