TRACHEAL GAS INSUFFLATION REDUCES THE TIDAL VOLUME WHILE PACO2 IS MAINTAINED CONSTANT

Objective: The aims of the present study were two-fold: first, to conf irm the effect of tracheal gas insufflation (TGI) throughout the respi ratory cycle on alveolar ventilation at various catheter flows and con stant total inspired VT as an adjunct to conventional volume cycled me chanical ventilation in patients with acute lung injury; second, to te st the efficacy of TGI in the reduction of toal V(T), peak and mean ai rway pressure while maintaining PaCO2 in its baseline value. The hemod ynamic effect and the consequences on oxygenation as result of the red uction of V(T), were also estimated. Design: Prospective study of pati ents with acute lung injury requiring mechanical ventilation. Setting: 12 bedded, adult polyvalent intensive care unit in a teaching hospita l. Patients: 7 paralyzed and sedated patients with acute respiratory f ailure were studied. All patients were clinically and hemodynamically stable without fluctuation of the body temperature. All patients were orally intubated with cuffed endotracheal tubes, and mechanically vent ilated with a standard circuit of known compliance. Interventions: Con tinuous flows (4 and 61/min) were delivered through a catheter positio ned 1 cm above carina while tidal volume or PaCO2 were maintained cons tant at their baseline value. Results: In this study a modest level of TGI significantly enhanced CO2 elimination in patients with acute res piratory failure. Improved ventilatory efficiency resulted from the fu nctional reduction of dead space during TGI allowing the same PaCO2 to be maintained at the same frequency with lower tidal volume and lower airway pressure requirement. Tidal volume, peak and mean airway press ure decreased linearly with catheter flow, without significant changes in oxygenation, while PaCO2 remained stable. Conclusion: The results of this study suggest that TGI may be an useful adjunct mode of mechan ical ventilation that limits alveolar pressure and minute ventilation requirements.