Effects of Pulmonary Edema on Lung Mechanics

Abstract

It is useful to distinguish between cardiogenic and noncardiogenic pulmonary edema when considering the effects of pulmonary edema on lung mechanics. Pulmonary edema can be caused by an increase in the hydrostatic and oncotic pressures favoring fluid transudation from the capillaries to the pulmonary interstitium and airspaces, or by increased permeability of the pulmonary capillary endothelium. In some patients, a combination of altered driving pressures and permeability may contribute to the development of pulmonary edema. Since left heart failure and increased left atrial pressure are by far the most common causes of increased driving pressures favoring fluid transudation, this type of pulmonary edema is often labelled cardiogenic. In the adult respiratory distress syndrome (ARDS), or noncardiogenic pulmonary edema, pulmonary edema develops in the setting of normal driving pressures. Considerable clinical and experimental evidence supports the concept that the development of pulmonary edema in ARDS is causally related to increased permeability of the pulmonary capillary endothelium.' Since the alterations in lung mechanics associated with cardiogenic pulmonary edema and ARDS differ, the two types of pulmonary edema will be considered separately. These differences may have clinical implications in the therapy of both cardiogenic pulmonary edema and ARDS.