Mechanical and chemical damage to lung tissue caused by meconium aspiration.

We investigated the effects of meconium on the lungs of an adult rabbit model to distinguish between mechanical obstruction of airways and chemical pneumonitis. After the rabbits were anesthetized and intubated, 20% human meconium in saline was instilled into the trachea. Arterial and mixed venous blood gases, functional residual capacity, cardiac output vascular pressures, calculated venous admixture, and pulmonary vascular resistance were measured. Sections of affected lung tissue were examined microscopically. The results were consistent with an early mechanical obstruction of airways with gradual development of chemical pneumonitis over 48 hours.