Airway obstruction in sheep with burn and smoke inhalation injuries.

The goals of this study were (i) to compare the degree and (ii) temporal changes in airway obstruction in sheep with pulmonary injury induced by smoke inhalation and/or burn; (iii) to qualitatively assess the cellular and mucous content of obstructive material; and (iv) to statistically assess a possible relationship between the degree of airway obstruction and pulmonary dysfunction. Using masked histologic slides, we estimated the degree of luminal obstruction in all cross-sectioned airways. The mean degree of bronchial, bronchiolar, and terminal bronchiolar obstruction was significantly greater in animals with smoke injury alone or combined smoke inhalation and burn (S+B) injury, compared with animals with burn injury alone or uninjured animals (P < 0.05). In S+B animals, the degree of bronchial obstruction was maximal at 24 h, with a progressive decrease over 72 h. In contrast, the degree of bronchiolar obstruction increased over time. Qualitatively, bronchial casts were largely composed of mucus at early times after injury, whereas neutrophils were the principal component of bronchiolar obstructive material. Localization of specific mucin subtypes in S+B tissues suggests that increasing bronchiolar obstruction is derived, in part, from upper airway material. Multiple linear regression analysis of airway obstruction scores compared with PaO2/FIO2 values showed a correlation coefficient of r = 0.76, with bronchial and bronchiolar scores predictive of PaO2/FIO2, (P < 0.05). These results suggest that strategies to remove or decrease formation of upper airway obstructive material may reduce its deposition into small airways and parenchyma and may improve respiratory function in victims of smoke inhalation injury.