Tracheobronchial and pulmonary histopathology following conventional and high-frequency jet ventilation

The advent of high-frequency jet ventilation (HFJV) as an alternative method of respiratory support for newborns has been implicated as a causative agent of necrotizing tracheobronchitis (NTB). We conducted a controlled trial of prolonged HFJV and conventional mechanical ventilation (CMV) in adult cats to determine effects on airway injury related to mode of ventilation and placement of the jet injector (proximal vs distal trachea). Fifteen cats were randomly assigned to either high-frequency positive pressure ventilation, proximal injection jet ventilation, or distal injection jet ventilation. The animals were ventilated for more than 33 hours. Post mortem, the trachea and respiratory tree were removed en bloc and fixed in formalin. A pathologist, unaware of the mode of ventilation, examined tracheobronchial histology and assigned scores using a technique previously described. Lung parenchymal tissue was also assessed using a similar grading system. Statistical analysis (Kruskal-Wallis analysis of variance) demonstrated no significant differences between tracheobronchial or lung parenchymal histopathology regardless of the mode of ventilation. We conclude that (1) the adult cat serves as a useful model for evaluating histopathologic effects of prolonged ventilation, (2) the etiology and pathogenesis of airway injury appears to be multifactorial, and the mode of ventilation is only one of many contributing variables, and (3) previously demonstrated differences between CMV and HFJV may be related to a much shorter duration of ventilation.