Pulmonary sup 99m Tc-human serum albumin clearance and effects of surfactant replacement after lung lavage in rabbits

Abstract

Objective Pulmonary clearance of technetium-labeled human serum albumin was measured in order to investigate whether the surfactant layer is a rate-limiting factor for the permeability of the alveolar-capillary membrane for^99m Tc-labeled albumin. Design Prospective, randomized, controlled trial. Setting Research laboratory. Subjects Nineteen white 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 animals were not lavaged and served as an untreated, healthy control group. All animals were ventilated with high pressures. Measurements and Main Results sup 99m Tc-labeled albumin was nebulized into the inspiratory line of the breathing circuit with an air jet nebulizer. The clearance measurements were then immediately started. Gamma camera images were obtained in 1-min frames for 120 mins and stored in a 64 times 64 image matrix in a computer. In group 1 animals, surfactant restored blood gases to near normal, and all animals except one had bi-exponential clearance 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. All group 2 animals also had bi-exponential clearance curves of the tracer (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 fast (p < .01) and slow (p < .01) components were significantly different between groups 1 and 2. Group 3 had a monoexponential half-life of 580 +/- 225 mins. Conclusions The use of^99m Tc-human serum albumin as a tracer molecule is possible and feasible. The clearance of this tracer is, in part, determined by the integrity of the pulmonary surfactant system, as it is with^99m Tc-diethylenetriamine pentaacetate. (Crit Care Med 1996; 24:1518-1523)