EFFECT OF HIGH-FREQUENCY VENTILATION ON THE DEVELOPMENT OF ALVEOLAR EDEMA IN PREMATURE MONKEYS AT RISK FOR HYALINE-MEMBRANE DISEASE

High-frequency oscillatory ventilation (HFOV) permits adequate gas exchange but avoids the large phasic pressure-volume excursions of conventional mechanical ventilation (CMV); such avoidance may reduce the lung injury associated with hyaline membrane disease (HMD). We hypothesized that premature monkeys ventilated from birth with HFOV would have reduced lung injury compared to those assigned to CMV. Macaca nemestrina were delivered at 134 days (80% of term gestation) and ventilated from the first breath with either HFOV (n = 10) or CMV (n = 10). The mean airway pressure (PawBAR) was kept at 15 cm H2O pressure in HFOV animals; in CMV animals PawBAR was increased from 8 cm H2O at 2 h to 13 cm H2O at 6 h to prevent hypoxemia. At the conclusion of the 6-h experiment the HFOV animals had better oxygenation (p < 0.05) and less evidence of HMD by chest radiograph (p < 0.05). At 6 h of age a piece of the right middle lung lobe was removed, divided, and placed in fixatives for light and transmission electron microscopy. The lungs were subsequently inflated to 30 cm H2O pressure, and the right lower lobe was rapidly frozen in situ for morphometric studies. The proportion of peripheral lung tissue occupied by clear alveoli was greater in HFOV animals (66.3 +/- 14.8%) than in those assigned to CMV (44.2 +/- 16.9%, p < 0.01); less alveolar debris and fluid was present in the HFOV animals (12.7 +/- 9.9%) compared with CMV animals (27.1 +/- 12.5%, p < 0.02). However, qualitative assessment of lung cell damage by light and transmission electron microscopy was no different between the two groups. Compared to CMV, initiation of HFOV at birth in premature monkeys is associated with improved gas exchange and chest radiograph and less alveolar fluid and debris, but not reduced lung tissue injury at 6 h of age.