SHORT-TERM DISTRIBUTION KINETICS OF INTRATRACHEALLY ADMINISTERED EXOGENOUS LUNG SURFACTANT

The short-term distribution kinetics of exogenous surfactant distribution after intratracheal instillation was investigated in surfactant-deficient neonatal piglets during assisted conventional mechanical ventilation and by high-frequency jet ventilation using exogenous calf lung surfactant extract (CLSE) labeled with Tc-99m. Surfactant deficiency was induced by repeated bronchoalveolar lavage in piglets (1.2 +/- 0.4 kg, 1.4 +/- 0.7 d of age), and the short-term distribution kinetics of instilled, labeled CLSE were followed by gamma radioscintigraphy. Animals ventilated by either conventional mechanical ventilation or high-frequency jet ventilation showed similar improvement in arterial/alveolar oxygen ratios after surfactant replacement therapy (0.47 +/- 0.03 prelavage, 0.09 +/- 0.01 postlavage, 0.36 +/- 0.06 postsurfactant). This correlated directly with dynamic radioscintigraphic results showing that instilled CLSE began to distribute to the lungs within 5 s, and was present in substantial amounts in standardized symmetrical lung fields (central, right, and left; upper and lower) within 20 s of tracheal instillation. Subsequent measurements over 30 min showed continued presence of radiolabeled CLSE in all five areas of the lung, with no significant difference between conventional mechanical ventilation and high-frequency jet ventilation animals. Static (5-min) analyses at the end of this period showed that surfactant had distributed relatively symmetrically with 30% of the CLSE located in central regions, 40% in the upper lobes, and 30% in the lower lobes. In contrast, piglets receiving Tc-99m in saline showed nonuniform distribution with multiple filling defects noted throughout the lungs. The rapid kinetics and ventilation independence of CLSE distribution suggest that surfactant spreading phenomena after tracheal instillation may facilitate the delivery of exogenous surfactant into aerated lungs in therapeutic applications.