PULMONARY TC-99M-HUMAN SERUM-ALBUMIN CLEARANCE AND EFFECTS OF SURFACTANT REPLACEMENT AFTER LUNG LAVAGE IN RABBITS

Objective: Pulmonary clearance of technetium-labeled human serum album in was measured in order to investigate whether the surfactant layer i s a rate-limiting factor for the permeability of the alveolar-capillar y membrane for Tc-99m labeled albumin, Design: Prospective, randomized , controlled trial, Setting: Research laboratory, Subjects: Nineteen w hite New Zealand adult rabbits, Interventions: Three groups of rabbits were studied: group 1 animals received natural surfactant after lung lavage; group 2 animals underwent lung lavage only; and group 3 animal s were not ravaged and served as an untreated, healthy control group, All animals were ventilated with high pressures, Measurements and Main Results: Tc-99m-labeled albumin was nebulized into the inspiratory li ne of the breathing circuit with an air jet nebulizer. The clearance m easurements were then immediately started, Gamma camera images were ob tained in 1-min frames for 120 mins and stored in a 64 x 64 image matr ix in a computer, In group 1 animals, surfactant restored blood gases to near normal, and all animals except one had bi-exponential clearanc e curves, The half-life of the fast compartment was 35.9 +/- 6.4 mins, and the half-life of the slow compartment was 847.5 +/- 143.5 mins. A ll group 2 animals also had bi-exponential clearance curves of the tra cer (the half lives of the fast and slow compartments were 14.6 +/- 6. 7 and 459.8 +/- 167 mins, respectively). The half-lives of both the fa st (p<.01) and slow (p<.01) components were significantly different be tween groups 1 and 2, Group 3 had a monoexponential half-life of 580 /- 225 mins,Conclusions: The use of Tc-99m-human serum albumin as a tr acer molecule is possible and feasible. The clearance of this tracer i s, in part, determined by the integrity of the pulmonary surfactant sy stem, as it is with Tc-99m-diethylenetriamine pentaacetate.