In vitro and in vivo intrapulmonary distribution of fluorescently labeled surfactant.
OBJECTIVE
To determine the distribution of endotracheally administered surfactant at the alveolar level in an animal model of acute respiratory distress syndrome.


METHODS
Prospective, randomized animal study.


METHODS
Research laboratory of a university hospital.


METHODS
Seventy-one male Sprague-Dawley rats, weighing 330-370 g.


METHODS
To measure surfactant distribution in vitro, a glass trough mimicking dichotomic lung anatomy was used to determine the spreading properties of bovine lung surfactant extract supplemented with fluorescent Bodipy-labeled surfactant protein B. To measure surfactant distribution in vivo, rats were anesthetized, and lipopolysaccharide was aerosolized (12 mg/kg body weight) to induce lung injury resembling acute respiratory distress syndrome; in control rats, buffered saline was aerosolized. Twenty-four hours later rats were anesthetized, tracheotomized, and mechanically ventilated (peak airway pressure = 20 mbar; positive end-expiratory pressure = 6 mbar; inspiration time = expiration time = 0.6 sec; Fio2 = 50%). Surfactant (bovine lung surfactant extract, supplemented with fluorescent Bodipy-labeled surfactant protein B; 50 mg/kg body weight) was applied as a bolus; in control rats, saline was administered as a bolus. Rats were ventilated for 5, 15, 30, or 60 mins (n = 8 or 9 for each group). Then, lungs were excised and sliced. Lung slices, divided into aerated (open), underinflated (dystelectatic), or collapsed (atelectatic) alveolar areas, were examined by both light and fluorescence microscopy.


RESULTS
In vitro experiments revealed that surfactant spread independent of glass trough geometry and lowered the surface tension to equilibrium values (25 mN/m) within a few seconds. In vivo experiments showed that administered surfactant distributed preferentially into underinflated and aerated alveolar areas. Furthermore, surfactant distribution was not affected by length of mechanical ventilation.


CONCLUSIONS
When conventional mechanical ventilation was used in lipopolysaccharide-induced lung injury, surfactant preferentially distributed into underinflated and aerated alveolar areas. Because surfactant rarely reached collapsed alveolar areas, methods aiding in alveolar recruitment (e.g., open lung concept or body positioning) should precede surfactant administration.
Diemel
Robert V
RV
Department of Anesthesiology and Critical Care Medicine, The Leopold-Franzens-University of Innsbruck, Innsbruck, Austria.
Walch
Monika
M
Haagsman
Henk P
HP
Putz
Günther
G
D000818:Animals; D001896:Boron Compounds; D004195:Disease Models, Animal; D005456:Fluorescent Dyes; D006801:Humans; D007231:Infant, Newborn; D008297:Male; D008856:Microscopy, Fluorescence; D011650:Pulmonary Alveoli / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012121:Respiration, Artificial; D012127:Respiratory Distress Syndrome, Newborn / Q000378:metabolism; D013501:Surface-Active Agents / Q000008:administration & dosage / Q000378:metabolism*; D014018:Tissue Distribution
C095489:4,4-difluoro-4-bora-3a,4a-diaza-s-indacene; D001896:Boron Compounds; D005456:Fluorescent Dyes; D013501:Surface-Active Agents