Detection of changes in lung tissue composition by multiple indicator dilution (MID)

To examine the potential utility of MID for distinguishing between hydrostatic and permeability edema, saline with 4.5% albumin (to mimic permeability edema) or 4.5% dextran (hydrostatic edema) was instilled in the airways of isolated perfused rabbit lungs. Boluses containing FITC-dextran (F), 14C-diazepam (D), 3HOH (3H) or 14C-phenylethylamine (PEA) were injected into the pulmonary artery followed by sampling from the left atrium. F, D, 3H and PEA were used as vascular reference, extravascular plasma protein, extravascular water and endothelial surface indicators respectively. The figure shows that increased extravascular water was detected in both hydrostatic and permeability edema. Extravascular plasma protein was detected only in permeability edema and perfused sur-face area was virtually unaffected by edema.