Distribution of a second dose of exogenous surfactant in rabbits with severe respiratory failure

Newborn infants with respiratory distress who fail to respond to surfactant treatment receive a second dose of surfactant. The effect of this strategy on the distribution of surfactant to the lung is unknown. We therefore investigated the distribution of the first (100 mg/kg body weight) and second dose (50 mg/kg body weight) of surfactant (Alveofact) in lung-lavaged rabbits (n = 6). We used 141Ce- and 103Rn-labeled microspheres that were mixed with the first and second dose of surfactant, 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 the rabbits were killed, and the lungs were cut into 200 pieces. The radioactivity of Ce and Rn microspheres was measured and distribution histograms were obtained. Histograms of the first, second, and the total dose of surfactant showed similar nonuniform distribution. Correlation coefficients of the Ce and Rn radioactivity in the different lung lobes widely ranged per lung lobe per rabbit. In addition, the percentage of the number of lung pieces that received an amount of surfactant that 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 second dose, respectively. This indicates that the second dose was directed both to areas that initially received surfactant and to areas that were still surfactant-deficient. The surfactant-deficient areas were aerated after this second dose, resulting in a further rise in PO2.(ABSTRACT TRUNCATED AT 250 WORDS)