Increase of the oxygenation and decrease of the intrapulmonary peak pressure at constant mean airway pressure using high-frequency jet ventilation in adult rabbits with lavage-induced severe respiratory distress syndrome compared to conventional mechanical ventilation.

Abstract

Reports are contradictory about the value of high-frequency jet ventilation (HFJV) in the treatment of respiratory distress syndrome (RDS) [10, 11, 18 - 1, 2, 22, 25]. In a preliminary study on rabbits with healthy as well as surfactant deficient lungs, caused by lung lavage, at a constant mean airway pressure (MAP) and 20% inspiration time, the influence of the jet ventilation frequencies of 1, 3, 5, 10, 15 and 20 Hz (cycles per second) on the pressure oscillations along the airways as well as on blood gas and cardiac parameters were investigated. It was presumed that the breathing level, e.g. functional residual capacity plus 50% of the tidal volume is the same at constant MAP. The results during HFJV are compared to those of conventional mechanical ventilation (CMV). With increasing frequency the peak airway pressure (PAP) clearly decreased on both groups, while the self controlled positive end-expiratory pressure (AUTO-PEEP) increased. That means, the amplitude of the pressure oscillations became smaller and smaller, indicating that the danger of mechanical lesions might be reduced by this mode of ventilation. The arterial oxygenation (PaO2) increased with frequency. A threefold higher PaO2 could be obtained at 10 Hz in the animals with RDS lungs. The arterial carbon dioxide tension (PaCO2) increased nearly linear with the frequency in both groups. The inverse course of the arterial pH showed that it is possible to obtain at lower frequencies a respiratory alkalosis and at higher frequencies an acidosis. Optimal gas exchange could be obtained at about 10 Hz. Decreasing cardiac output with increasing frequency showed a good correlation to the pH in both groups. The effect was more influenced by the heart frequency than by the stroke volume especially in the RDS-group.