Under normal health conditions, there is a continuous flow of fluid content from the interstitial epithelial cells of the pulmonary capillaries into the surrounding alveolar interstitial. Moreover the interstitial has a number of lymph vessels available in the pulmonary tissue that remove the excess fluids. But when there is a pulmonary congestion they will be excess amount of fluid in the lungs and this can cause various life threatening complications.
There are various causes of pulmonary congestion that include an increase in hydrostatic pressure and increased capillary permeability. In other cases there may be increased hydration and reduced osmotic pressure that leads to the collection of extra vascular fluid around the lungs. If there is a transfusion reaction it could also lead to pulmonary congestion. A reduction in the production of plasma proteins leads to water in lungs.
When there is excess of fluid it the lungs it could also be a sign of ARDS or adult respiratory distress syndrome. The pulmonary congestion may be symmetrically or asymmetrically distributed. Asymmetrical congestion in the lungs can be identified by gravitational characteristics like lying comfortably on one side and unilateral emphysema. There may be a bronchial occlusion with unilateral venus occlusion and lymphatic obstruction. This condition is also observed in cases where there is removal of pleurothroax leading to pleural efflusion.