PEDIATRICS Vol. 84 No. 2 August 1989, pp. 304-311
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Determinants of Tracheobronchial Histologic Alterations During Conventional Mechanical Ventilation

Thomas E. Wiswell MC1, Barbara S. Turner AN1, John A. Bley VC1, David L. Fritz VC1, and Robert E. Hunt VC1

1 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

It was hypothesized that diverse mechanisms may influence upper airway injury during mechanical ventilation. To assess the roles of several factors in the propagation of such injury, the tracheobronchial histologic changes in 53 newborn piglets were compared following conventional positive pressure ventilation. Eight animals were assigned to each of four positive pressure ventilation groups at"low" settings (an FiO2 of 0.25, a frequency of 10 breaths per minute, a peak inspiratory pressure of 20 cm H2O, a positive end-expiratory pressure of 4 cm H2O, a flow rate of 10 L/min, and an inspiratory time to expiratory time ratio of 1:2): (1) positive pressure ventilation with no hypotension or hypoxemia; (2) positive pressure ventilation with hypotension; (3) positive pressure ventilation with hypoxemia; and (4) positive pressure ventilation with both hypotension and hypoxemia. In addition, eight piglets were assigned to each of two positive pressure ventilation groups at "high" settings (greater frequency [40 breaths per minute], higher peak inspiratory pressure [40 cm H2O], and greater flow rate [17 L/min]): (1) positive pressure ventilation with no hypotension or hypoxemia; and (2) positive pressure ventilation with both hypotension and hypoxemia. The changes were mild and similar among the first three positive pressure groups at low settings. However, the injury scores of the combined hypotension and hypoxemia group (group 4) were greater than those of the former three positive pressure ventilation groups (P < .004). The piglets receiving positive pressure ventilation at high settings with no hypotension or hypoxemia (group 5) had no more injury than those in the first three groups receiving positive pressure ventilation. with concurrent hypotension and hypoxemia were associated with more damage in the trachea than high settings alone (P = .0019). Factors that affect tissue oxygenation or cause direct trauma appear to influence the degree of histopathologic alterations during mechanical ventilation.

Key Words: airway injury • newborn piglets • asphyxia • hypotension • mechanical ventilation

Submitted on July 1, 1988
Accepted on August 11, 1988