Determinants of tracheobronchial histologic alterations during conventional mechanical ventilation
Wiswell, T.E.; Turner, B.S.; Bley, J.A.; Fritz, D.L.; Hunt, R.E.
Pediatrics 84(2): 304-311
1989
ISSN/ISBN: 0031-4005 PMID: 2748259 Document Number: 331254
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 pressures 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 a "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 ventilations 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. High settings 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.