Effects of albumin and urea on hydrostatic edema in the perfused lung

Hydrostatic interstitial pulmonary edema was induced in isolated perfused canine lungs to evaluate the effects of treatment with osmotic agents. In 14 preparations after induced venous hypertension adding fluid weights of 20, 30, 40, or 60 g representing 33–100% of normal lobe weight, venous pressure was returned to levels of zero or below without additional treatment. Albumin (25 g) was added to 23 preparations and urea (10 g) added to 10 lungs prepared in a similar fashion. Reductions in pulmonary venous oxygen tension and effective compliance occurred at all levels of edema and persisted after release of venous constriction. Albumin improved venous PO₂ only after the minimal load but there was no significant effect on pulmonary compliance. No improvement in either parameter occurred after urea treatment. Significantly lower weights after albumin or urea treatment were noted after varied fluid loads but were not accompanied by proportional improvement in lung function. In the isolated lung preparation with no outlet for fluid excretion, the therapeutic effectiveness of osmotic agents alone is obviously limited, but the deleterious effects of hydrostatic interstitial edema are not readily reversed by addition of osmotic agents to the perfusate. The previously noted adverse effects of mannitol do not seem to be explained adequately on the basis of lower molecular weight alone since urea did not prove to be deleterious in this preparation.