Neutrophil elastase and acute pulmonary damage in neonates with severe respiratory distress syndrome

This study evaluated possible acute effects of neutrophil elastase on neonatal pulmonary morbidity. The activity of free elastase and α₁- proteinase inhibitor as well as concentrations of elastase-α₁-proteinase inhibitor in tracheal aspirate fluid of neonates with severe respiratory distress syndrome (fraction of inspired oxygen > 0.6, mechanical ventilation) were analyzed between 6 and 36 hours after surfactant replacement therapy. One hundred forty neonates were included in this prospective study. Characteristics, disease severity, and ventilatory requirements were nearly identical in both groups. All patients were treated with natural porcine surfactant (Curosurf) at an age of 2 to 15 hours. In 42 neonates (30%) considerable activities of free elastase were detected (805 μg/L; 100 to 1850 [median, 25th to 75th percentile]); in 98 neonates (70%) who had protective levels of α₁-proteinase inhibitor, no elastase activity was detected. The average concentrations of elastase-α₁-proteinase inhibitor were significantly increased in patients with free elastase activity when compared with those of the nonelastase group. In logistic regression analyses, 28-day outcome data showed a pronounced increase in risk of pulmonary interstitial emphysema for patients with free elastase activity in tracheal aspirate fluid. The incidence of other pulmonary and nonpulmonary complications was very similar in both groups. It is concluded that elastolytic damage and barotrauma may both contribute to acute pulmonary injury in the early stages of respiratory distress syndrome.