[Ventilation by high frequency oscillations in adults. An experimental study of conditions and methods]

A hydraulic pump with an adjustable stroke delivering up to 145 ml at 1 to 45 Hz has been used to ventilate adult pigs of a weight between 60 and 140 kg. After tracheotomy the curarized animals were connected to the pump by a metallic tube through which a bias flow was directed. This flow (FiO2 0.35) was humidified by a special ceramic device and aspirated at the distal end of the tube. It was demonstrated that under these conditions gaz exchange was well maintained with oscillations between 15 and 35 Hz. Higher frequencies were needed for the heavier animals. Blood gas measurements of samples from segmental pulmonary veins demonstrated regional differences in gas exchange. These could be modified by adjusting the oscillation frequency. Reinhalation of gas could be prevented by an increase of the bias flow. Alveolar recruitment by initial pulmonary inflation by a pressure of 18 +/- 2 cm H2O is required for adequate oxygenation. Maintenance of adequate elimination of CO2 required a bias flow of 35 +/- 5 l/min. Mean pressure in the airways was maintained at 12 +/- 1 cm H2O. This pressure determines the value of PaO2. Ordinary endotracheal tubes tend to collapse during the sucking phase of the pressure cycle. Rigid or armed tubes are required. They must allow for aspiration of the bias flow from the distal end of the tube.