Tracheal mucosal damage after aspiration. A scanning electron Microscope study

Aspiration of gastric contents causes severe pneumonitis, but the effects of such aspiration on the large airways have not been well studied. To evaluate the effects of gastric contents on the tracheal mucosa, 63 healthy A/J mice were anesthetized and aspirated either sterile saline (pH, 5.9) (Group I), hydrochloric acid (pH, 1.5) (Group II), canine gastric juice (pH, 1.5) (Group III), or canine gastric juice (pH, 5.9) (Group IV). Tracer studies showed that the average amount aspirated was 15% of the administered dose. Animals from each group were killed by cervical dislocation at 1, 6, 24, 48, and 72 h and 7 days after aspiration. Examination of the tracheas by scanning electron microscopy revealed normal mucosa in all Group I animals. Tracheas from Group II animals killed between 6 and 48 h after aspiration showed desquamation of the superficial cell layer with complete loss of ciliated and nonciliated cells. Regeneration was noted at 3 days with complete recovery by 7 days. Tracheas from Group III animals had similar changes but regeneration was delayed, whereas those from Group IV had mild desquamation with delayed regeneration. The lungs of group I animals were normal, and those of animals in Group II through IV showed only small widely separated areas of inflammation. We conclude that (1) gastric contents cause marked damage to the tracheal mucosa even when the amount aspirated is too small to induce a clinically significant pneumonia, (2) damage is more severe when the pH of the gastric content is low, and (3) gastric juice may contain substances that delay healing.