The value of edema fluid protein measurement in patients with pulmonary edema

Alveolar fluid and plasma proteins were analyzed in 24 patients with florid pulmonary edema, in 21 of whom pulmonary capillary wedge pressure (Pcw) was also measured. In all patients with Pcw less than 20 mm Hg, the edema fluid to plasma protein ratio exceeded 0.6; the mean edema fluid to plasma protein ratio in the four patients with cardiogenic edema (increased Pcw) was 0.46. In the 21 patients in whom full data were available, the net intravascular filtration force (Pcw - plasma colloid osmotic pressure) was less than -4 mm Hg, the value at which (according to others) pulmonary edema should occur, in only 10. When the interstitial colloid osmotic pressure, approximated by the osmotic pressure of edema fluid protein, was added, the net filtration force became positive in 17 of 21 patients. Comparison of the protein concentrations of edema fluid and plasma aids in the diagnostic separation of increased permeability from high hydrostatic pressure edema and adds to our understanding of the relative osmotic and hydrostatic forces that contribute to pulmonary edema when the alveolar-capillary membrane is damaged.