DISTRIBUTION OF A 2ND DOSE OF EXOGENOUS SURFACTANT IN RABBITS WITH SEVERE RESPIRATORY-FAILURE

Newborn infants with respiratory distress who fail to respond to surfa ctant treatment receive a second dose of surfactant. The effect of thi s strategy on the distribution of surfactant to the lung is unknown. W e therefore investigated the distribution of the first (100 mg/kg body weight) and second dose (50 mg/kg body weight) of surfactant (Alveofa ct) in lung-lavaged rabbits (n = 6). We used Ce-141- and Rn-103-labele d microspheres that were mixed with the first and second dose of surfa ctant, respectively. Arterial PO2 increased from 5.7 +/- 1.1 to 10.6 /- 2.0 kPa (p < 0.05) (mean +/- SD) after the first and from 20.1 +/- 3.8 to 30.1 +/- 2.5 kPa (p < 0.05) after the second dose. Thereafter t he rabbits were killed, and the lungs were cut into 200 pieces. The ra dioactivity of Ce and Rn microspheres was measured and distribution hi stograms were obtained. Histograms of the first, second, and the total dose of surfactant showed similar nonuniform distribution. Correlatio n coefficients of the Ce and Rn radioactivity in the different lung lo bes widely ranged per lung lobe per rabbit. In addition, the percentag e of the number of lung pieces that received an amount of surfactant t hat was less than the calculated endogenous surfactant pool decreased from 12.5 +/- 3.2% to 8.5 +/- 3.0% (p < 0.05) after the first and seco nd dose, respectively. This indicates that the second dose was directe d both to areas that initially received surfactant and to areas that w ere still surfactant-deficient. The surfactant-deficient areas were ae rated after this second dose, resulting in a further rise in PO2. We c onclude that a second dose of surfactant does not lead to homogeneous distribution of surfactant but does result in a significant rise in PO 2 that is probably due to increased aeration after the second dose of surfactant, which may be partially related to an additional recruitmen t of alveoli after the second dose of surfactant.