Airway aspiration of hydrochloric acid in sheep

We have compared the effects of aspiration of 2.5 ml/kg of 0.1 N hydrochloric acid (HCl) on groups undergoing normal saline aspiration (2.5 ml/kg) and a sham control in unanesthetized sheep with chronic lung lymph fistula for up to 148 hr. Significant changes in pulmonary lymph flow and cardiopulmonary variables occurred in the airway acid group within the first 48 hr, as compared to saline and sham control. In the HCl group lymph flow increased from a baseline of 8.5 ± 1.5 to 21.8 ± 3.0 ml/hr (mean ± SEM) at 2 hr. Pulmonary vasoconstriction occurred at this time with significant elevations of lymph thromboxane B₂ from a baseline of 400 ± 11 to 2,090 ± 690 pg/ml. During the early acid aspiration phase products of lipid peroxidation were noted to increase from 0.29 ± 0.03 to 0.81 ± 0.17 absorbance units. Associated with elevated lymph flow was a significant drop in cardiac index in the airway-acid-aspirated group (6.59 ± 0.52 to 5.53 ± 0.36 L/min/m²) and a rise in bronchial blood flow from 9.8 ± 1.7 to 63.7 ± 8.9 ml/min. These data suggest that a moderate airway acid injury created by 2.5 ml/kg of HCl results in acute pulmonary damage with the release of several potential mediators which may be responsible for the observed effects. The long-term acid-injured animals survived for up to 1 week following the aspiration procedure with evidence of resolution of lung damage by wet-weight dry-weight evaluation of lung (normal lab control = 4.0 ± 0.2, and 148 hr after acid = 4.5 ± 0.3) and microscopic evidence of minimal persistent injury. These data document the pulmonary damage and repair resulting from airway acid instillation.