PEDIATRICS Vol. 85 No. 1 January 1990, pp. 70-78
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Different High-Frequency Ventilator Strategies: Effect on the Propagation of Tracheobronchial Histopathologic Changes

Thomas E. Wiswell MC, USA1, John A. Bley VC, USA1, Barbara S. Turner NC, USA1, Robert E. Hunt VC, USA1, and David L. Fritz VC, USA1

1 From the Divisions of Medicine, Pathology, and Veterinary Medicine, Walter Reed Army Institute of Research; and the Nursing Research Service, Walter Reed Army Medical Center, Washington, DC

To assess the role of high-frequency ventilator strategy in the propagation of airway injury, we compared the tracheobronchial histologic alterations in 20 newborn piglets ventilated for 8 hours with high-frequency flow interruption (HFFI). Ten animals were assigned to HFFI with a strategy of continuous pulsations at a frequency of 10 Hz and a mean airway pressure of 16 cm H2O. Ten piglets were treated at identical settings except for 10 one-second baseline pauses per minute to a positive end-expiratory pressure of 5 cm H2O. A semiquantitative scoring system was used to grade light microscopic tissue alterations in the trachea, carina, and mainstem bronchi. Ultrastructural changes were evaluated with scanning electron microscopy. The HFFI-continuous-treated piglets had significantly more damage in all areas than the HFFI-baseline pause group (P < .001). The upper tracheas of animals in both groups were altered to a greater extent than the lower tracheas (P < .007). In addition, numerous "skip" areas of injury were noted throughout the tracheas. High-frequency ventilator strategy is a determinant of the severity of airway histologic changes. Factors that adversely affect tissue oxygenation or cause direct mechanical trauma may also influence the degree of injury. Optimal operating characteristics and limitations of different high-frequency devices must be assessed before their use in human neonates.

Key Words: high-frequency ventilation • airway injury • newborn piglet • mechanical ventilation

Submitted on September 20, 1988
Accepted on March 7, 1989