Conventional
ventilators are frequently used at high rates in the
intensive care nursery to achieve adequate oxygenation and ventilation with reduced peak inspiratory pressure. The efficacy and limitations of
high frequency positive-pressure ventilation (HFPPV) using a conventional
ventilator were studied by comparing the cardiopulmonary effects of HFPPV with those of
high frequency jet ventilation (HFJV) in an animal model of
respiratory failure. Sixteen saline-lavaged rabbits were ventilated with either HFPPV or HFJV for 2 h using rates of 200 breaths/min, inspiratory to expiratory ratio of 1:2, and FIO2 of 1.0. As controls an additional eight lavaged rabbits were ventilated at conventional rates (40 to 60 breaths/min). Proximal peak inspiratory pressure as indicated on the
ventilator manometer or drive pressure was adjusted to maintain acceptable blood
gases. Cardiac output (CO) was measured by thermodilution. Although there was a significant decrease in cardiac function over time, there were no significant differences between the groups in CO or stroke volume. Satisfactory oxygenation and ventilation were maintained in all groups. Static respiratory system compliance and mean airway pressure were similar among the groups. Histologic examination of the lungs revealed no differences between the three
ventilator groups. The results of this study indicate that both HFPPV and HFJV are effective in short-term maintenance of normal blood
gases in
respiratory failure without any discernable differences in their effects on cardiovascular function. At very high rates, however, increases in VT are not possible with HFPPV, which limits its usefulness and flexibility in
respiratory failure.