Experimental meconium aspiration in guinea pigs.

The effects of aspirated heavy human meconium and clear human amniotic fluid on newborn guinea pig lungs were compared with the changes these solutions induced in lungs subjected to acute asphyxiation. No specific meconium-induced chemical pneumonitis was observed. Histologic changes in the form of necrosis and infiltration of the lungs were similar in pups that aspirated meconium and those that aspirated clear amniotic fluid; the only difference was in the distribution of these changes, which could be explained by the different consistencies of the two solutions. In the lungs of newborn pups that were exposed to 120 minutes of maternal asphyxia, had pH below 7.10, and aspirated the above fluids, additional dominant changes appeared in the form of diffuse intra-alveolar hemorrhage and alveolar wall destruction. These histologic studies indicate that deeply aspirated meconium does not cause the pulmonary vascular changes considered characteristic of meconium aspiration syndrome. However, aspirated meconium did affect the vascular system of the asphyxiated lungs to a significant degree.