Effect of decreased plasma colloid osmotic pressure on development of pulmonary edema in dogs.

The effect of decreased plasma colloid osmotic pressure on the development of pulmonary edema was studied in anesthetized dogs. Lung lymph flow was used aa a sensitive and reliable indicator of fluid filtration rate in the lung. When plasma colloid osmotic pressure alone was reduced by slow infusion of saline, and hydrostatic pressure in the pulmonary vascular bed was maintained at normal level by exsanguination, lung lymph flow increased almost linearly with the reduction in colloid osmotic pressure, but was not increased more than five fold of the control, despite a reduction of 80% in the plasma colloid osmotic pressure. Furthermore, there was no evidence of fluid in the tracheal aspiration and no gross evidence of pulmonary edema. In contrast, both decrease in colloid osmotic pressure and increase in pulmonary capillary hydrostatic pressure produced a marked increase in lung lymph flow. This flow varied linearly with the level of the pulmonary artery wedge-plasma colloid osmotic pressure difference and approached twelve fold of the control, when the plasma colloid osmotic pressure was reduced by 73% and the pulmonary artery wedge pressure was elevated by 20 mmHg from the baseline. Our data indicate that decreased colloid osmotic pressure is not associated with the development of pulmonary edema, when there is no increase in pulmonary vascular hydrostatic pressure.