Smoke inhalation injury promotes exfoliation of the upper airway columnar epithelium. Tracheal tissues from sheep 30 min after smoke exposure show intact epithelial areas, areas of epithelial disruption with loss of columnar cells and areas denuded of columnar cells. In intact areas detaching ciliated cells can be seen raised above the apical surface. This study aims to assess cell-specific toxicity by examining intact epithelium after inhalation injury. The junctional adhesion integrity between columnar and basal cells and the type of cells initially being displaced were also studied using light (LM) and transmission electron microscopy (TEM). TEM assessment of intact areas of sheep tracheal tissue (n=3) 30 min after exposure showed secretory cell toxicity including extrusion of cytoplasmic contents. In cells with severe secretory cell cytoplasmic disruption, loss of desmosomal junctions between the secretory and adjacent ciliated cells was evident. The number of desmosomes visible between columnar cells and basal cells was reduced (2.8 ± 1.8) in smoke-exposed animals compared to those in uninjured animals (5.0 ± 2.7), p=0.008. Serial sections of intact regions found 52 cells being displaced from the epithelium. All detaching cells were identified as ciliated cells. These studies show that the acute effects of inhalation injury include selective secretory cell toxicity which is associated with loss of junctional adhesion mechanisms and displacement of ciliated cells. Improved understanding of acute hypersecretory responses and epithelial integrity after exposure to toxic agents may improve understanding of epithelial fragility in airway disease.

This study measured airway obstruction and bacterial invasion in systematically sampled lung tissue of burn victims at autopsy. Lung tissue from victims of combined smoke inhalation and burn injury (n = 5) and burn injury alone (n = 9) was examined histologically and the degree of bronchial and bronchiolar obstruction was measured. The walls of both bronchi and bronchioles were examined for bacterial invasion. Correlation analysis was performed for the association of airway obstruction with TBSA burn, number of ventilatory days, maximum inspiratory pressure, and days after injury. There was no significant difference in the mean degree of airway obstruction in smoke inhalation and burn victims compared with victims of burn-only injury (P > .05). Increased bronchiolar obstruction scores were detected in victims with pneumonia (55.3 ± 24.2%) compared with victims without pneumonia (9.3 ± 0.2%; P = .03). Bacterial invasion of the bronchial wall was present in one case, and invasion into the walls of bronchioles was seen in five cases. Burned children who died had extensive bronchiolar obstruction whether or not they had smoke inhalation injury. There was bacterial invasion into the airway wall in six of 14 cases (43%). Improved understanding of the mechanisms of airway obstruction is important for improved care of burned children.

This study examines the structural integrity of the airway epithelium in autopsy tissues from pediatric burn subjects. Methods A semi-quantitative score for the degree of airway epithelial integrity was made for seventy- two pediatric burn autopsies. Multivariate ordinal logistic regression was performed to identify relationships between epithelial integrity and conditions related to tissue fixation, time of death after injury, age, total body surface area burn (TBSA), extent of 3rd degree burn injury, presence of inhalation injury, ventilator days and pneumonia. Results No significant difference in epithelial integrity scores was identified between burn only cases and those with inhalation injury. Significant correlations with bronchiolar epithelial integrity scores were identified for age, p = 0.02, and percent 3rd degree burn injury, p = 0.02. There was no significant relationship between epithelial integrity and time between death and autopsy, p > 0.44. Conclusions Airway epithelial loss seen in autopsy tissue is not simply an artifact of tissue fixation. The degree of compromise correlates most strongly with age and degree of burn injury. Further studies are needed to identify physiological or critical care factors following burn injury that contribute to compromise in the structural and functional properties of the airway epithelium.

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