Pressure-release tracheal gas insufflation reduces airway pressures in lung-injured sheep maintaining eucapnia

Although tracheal gas insufflation (TCI) has proved to be a useful adjunct to mechanical ventilation, end-inspiratory as well as end-expiratory pressu res may increase. We investigated the ability of continuous-flow TCI to mai ntain eucapnia while reducing airway pressure (Paw) and tidal volume (VT). Seven sheep (36 +/- 2 kg) were ventilated using the Drager Evita 4 in the p ressure control plus mode where flow is released via the expiratory valve t o maintain constant inspiratory pressure. To avoid TCI-generated positive e nd-expiratory pressure (PEEP), a prototype reverse flow TCI tube was used. Two TCI flows (5 and 10 L/min) were investigated pre- and postsaline lavage -induced lung injury. inspiratory pressures and VT were significantly reduc ed as TGI flow increased. At 10 L/min TCI flow the carinal pressures (Pcar) and VT were reduced pre- and postinjury by 15% and 20%, and by 28% and 34% , respectively. Tidal volume to dead space ratio (V-D/V-T) decreased preinj ury from 0.49 +/- 0.1 to 0.18 +/- 0.2 and postinjury from 0.62 +/- 0.1 to 0 .33 +/- 0.1 at a TGI flow of 10 L/min. The combination of the reverse flow TCI tube and a ventilator with an inspiratory pressure relief mechanism kep t set end-inspiratory and end-expiratory pressures constant. This TCI syste m effectively reduced set Paw and Vr while maintaining eucapnia.