Effect of albumin infusion on pulmonary microvascular fluid and protein transport

Abstract

The effect of human albumin infusion on the dynamics of fluid and protein transport across the pulmonary microcirculation was studied. Lung lymph flow ( Q ̇ L ) from a chronic lung lymph fistula in unanesthetized sheep was used as a reliable indicator of transvascular fluid filtration rate ( Q ̇ L ). Lymph protein content was considered equal to interstitial protein content. Pulmonary vascular pressures, Q ̇ L , lymph and plasma proteins were continuously monitored. After a 4-hr baseline period, 50g of human, salt-poor albumin (400 cc) was infused over 0.5-hr. A hypersensitivity reaction occurred, in four studies, reflected in a large increase in pulmonary artery pressure and Q ̇ L . Mean data for the remaining six studies are summarized for baseline, after albumin infusion and 2 and 4 hr postinfusion. Microvascular pressure ( P mr, mm Hg) for the four periods was 8, 12, 8, and 8, while plasma colloid osmotic pressure ( π mv, mm Hg) was 21, 27, 24, and 24, respectively. Interstitial colloid osmotic pressure ( π mv) was 11, 11, 13, and 14 mm Hg. Q ̇ L was unchanged over the entire study period. We found that albumin infusion produced an immediate increase in plasma oncotic pressure and a transient increase in P mv. However, the colloid osmotic gradient between the interstitium and plasma returned to baseline by 4 hr despite a continued increase in plasma proteins as interstitial protein content increased in an equal manner. These data suggest a very transient, if any, decrease in lung extravascular fluid after albumin infusion.