Effect of hypoproteinemia on pulmonary and soft tissue edema formation

The effect of acute hypoproteinemia on the rate of fluid flux across the pulmonary and soft tissue microcirculation was studied in the unanesthetized sheep. Lymph flow was used to monitor fluid flux, a protein depletion of 30-50% of baseline value was produced by plasmapheresis. Vascular hydrostatic pressures and cardiac output were maintained constant with crystalloid infusion. The measured oncotic pressure in plasma, pi rho rapidly decreased as did the oncotic gradient between plasma and lymph. Lung and soft tissue lymph flow increased 2- to 3-fold immediately after protein depletion. Lung interstitial oncotic pressure, pi L, as measured in lymph, decreased to return the oncotic gradient and lymph flow to baseline by 24 h. Soft tissue oncotic gradient also returned to baseline by 24 h, but lymph flow remained significantly elevated for the next 48 h, indicating an increase in fluid flux unrelated to changes in oncotic pressure. Lymph flow rapidly returned to baseline when protein was returned. Protein depletion may alter the soft tissue interstitial matrix, allowing for edema formation. More effective mechanisms prevent this from occurring in the lung.