Thoracoscopic Findings and Pharmacokinetics of Inhaled Fluorescein in a Pig Model

Background: Fluorescein-enhanced autofluorescence thoracoscopy (FEAT) reveals regions of abnormal fluorescence in patients with primary spontaneous pneumothorax and in normal subjects. Some of these lesions are undetectable by white light thoracoscopy and it has been hypothesized that they represent underlying pleural and/or parenchymal abnormalities. Objectives: In order to standardize and evaluate this novel technique, we developed an animal model. Methods: Six pigs underwent thoracoscopy after the inhalation of nebulized sodium fluorescein by either volume-controlled mechanical ventilation or spontaneous ventilation. Pleural cavity and lung surface were inspected by white light thoracoscopy and FEAT during a period of 90 min. Fluorescence intensities were quantified in pleura and in blood. Regions of interest were examined postmortem for a histological assessment of the lesions. Results:FEAT lesions were observed in all animals, with a maximum intensity of the lesions 20–30 min after the onset of fluorescein administration. The plasma concentrations of sodium fluorescein reached a maximum after approximately 20 min. The microscopic findings suggest that fluorescein accumulates in the subpleural space of better ventilated lung areas. Conclusions:This is the first animal model using FEAT. Valuable information has been gathered but further investigations are required to explain the phenomena observed in humans and pigs.