TRACHEAL MUCOSAL DAMAGE AFTER ASPIRATION - A SCANNING ELECTRON-MICROSCOPE STUDY

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Abstract
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 1), HCl (pH 1.5, Group 2), canine gastric juice (pH 1.5, group 3, or canine gastric juice (pH 5.9, group 4). 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 1 animals. Tracheas from group 2 animals killed between 6-48 h after aspiration showed desquamation of the superficial cell layer with complete loss of ciliate and nonciliated cells. Regeneration was noted at 3 days, with complete recovery by 7 days. Tracheas from group 3 animals had similar changes, but regeneration was delayed; those from group 4 had mild desquamation with delayed regeneration. The lungs of group 1 animals were normal, and those of animals in groups 2-4 showed only small, widely separated areas of inflammation. Gastric contents cause marked damage to the tracheal mucosa even when the amount aspirated is too small to induce a clinically significant pneumonia. Damage is more severe when the pH of the gastric content is low. Gastric juice may contain substances that delay healing.