COMPARISON OF DIFFERENT MODES OF HIGH-FREQUENCY VENTILATION IN SURFACTANT-DEFICIENT RABBITS

Various modes of high-frequency ventilation (HFV) have been developed to avoid the disadvantages of conventional mechanical ventilation. In the present study, we examined the hypothesis that high-frequency osci llation (HFO) is superior to high-frequency positive pressure ventilat ion (HPPV) and combined high-frequency ventilation (CHFV) in surfactan t-deficient rabbits. The aim of the ventilator strategy was to adjust the mean airway pressure to 2 cm above critical opening pressure of th e inflation limb of the respiratory system pressure volume (P/V) curve , achieve a normal tidal volume (VT) (5 ml/kg body weight) and apply r epeated sustained inflations. We studied the effect of these HFV modes on oxygenation, lung mechanics and lung histology in 15 New Zealand W hite rabbits during a 6-hour experiment. Statistically, the HFO group demonstrated significantly better oxygenation (P < 0.05), lung mechani cs (lung stability index: P < 0.05), and better lung tissue histology compared to the HPPV and CHFV groups. In contrast to the HPPV and CHFV groups, the P/V curves of the HFO group showed significant recovery o ver the 6-hour period after lavage. The lungs of the HFO-treated group had a more uniform distribution of alveoli and less overdistention th an the HPPV group (P < 0.002), and less atelectasis than the CHFV grou p (P < 0.05). The HFO group had less lung injury than the CHFV groups (P < 0.01) and its lungs contained significantly less water than both other groups (P < 0.05). We conclude that the relationship between mea n and end-expiratory pressures impacts strongly on both oxygenation an d the progression of injury during HFV at the same mean airway pressur es. The HFO group showed less acute lung injury than the other ventila tory groups. (C) 1996 Wiley-Liss, Inc.