Meconium induces only localized inflammatory lung injury in piglets

Neonatal meconium aspiration often produces severe respiratory distress due to an inflammatory pulmonary injury, but the extension of this damaging reaction to the noncontaminated lung regions is still uncertain. To investigate the presence of generalized pulmonary inflammatory response, 31 anesthetized and ventilated neonatal piglets (1-3 d) were studied. Meconium (n = 16) or saline (n = 15) was instilled unilaterally into the right lung, and analysis of the lung tissue or bronchoalveolar lavage (BAL) fluid from both lungs was performed after 12 h. Meconium increased the wet/dry weight ratio, histologic tissue injury score and tissue myeloperoxidase activity as well as BAL fluid total cell count in the contaminated lung. Tumor necrosis factor-alfa concentrations in BAL fluid did not however differ significantly. Furthermore, in the meconium-instilled lungs the tissue and lavage fluid catalytic activity of phospholipase A2 (PLA2) and tissue PLA2 group-I and group-II concentrations were significantly elevated. Although BAL fluid catalytic activity of PLA2 was moderately increased also in the meconium noninstilled lung, significant inflammatory injury in this lung was absent. The results thus indicate that meconium aspiration induces severe local inflammation and lung injury, but significant generalized pulmonary inflammatory damage in the pathogenesis of meconium aspiration syndrome is unlikely.