ObjectivesTo determine the efficacy of tracheal gas insufflation delivered by two different catheter designs on CO2elimination when used in conjunction with high-frequency oscillatory ventilation.DesignA nonrandomized before and after trial. Each animal served as his own control.SubjectsTen mongrel dogs weighing 20.9 plus minus 1.9 kg. Four animals were assigned to a normal lung group and six animals underwent lung injury by large volume saline lavage.InterventionPermissive hypercapnia was allowed to occur by selecting oscillator settings that would lead to alveolar hypoventilation. Proximal mean airway pressure was kept constant. Tracheal gas was insufflated at 1 cm above the carina for 30-min periods at gas flows of 5 to 15 L/minMeasurements and Main ResultsCarinal pressure, hemodynamic parameters (cardiac output, mean arterial pressure, pulmonary arterial pressure, pulmonary artery occlusion pressure), and gas exchange parameters (PaCO2, PaO2, PaO2/FIO2, shunt fraction, DO2) were measured.For the normal dogs, at catheter flow of 15 L/min, the forward thrust catheter increased carinal pressure and PaO sub 2/FIO sub 2 by 30% (p less than .003) and 105% (p less than .005), respectively. The forward thrust catheter reduced PaCO2by 40% (p less than .04). The reverse thrust catheter increased PaO2/FIO2by 102% (p less than .001) and decreased carinal pressure and PaCO2by 44% (p less than .001) and 34% (p less than .003), respectively. For the injured dogs, at catheter flow rate of 15 L/min, the forward thrust catheter increased carinal pressure, PaO2, and PaO2/FIO2by 6% (p less than .001), 23% (p less than .001) and 24% (p less than .02), respectively. The forward thrust catheter reduced PaCO2by 29% (p less than .002). The reverse thrust catheter increased PaO2and PaO2/FIO2both by 11% (p less than .02) and reduced carinal pressure and PaCO2by 23% (p less than .001) and 18% (p less than .002), respectively.ConclusionsTracheal gas insufflation is capable of improving oxygenation and ventilation in acute lung injury when combined with high-frequency oscillatory ventilation. The addition of this second gas flow at the level of the carina raises or lowers distal airway pressure, the magnitude of which is dependent on the direction and rate of gas flow. The beneficial effects of tracheal gas insufflation may be tempered by the long-term effects of altering distal airway pressure; lowering distal airway pressure may lead to atelectasis, whereas raising distal airway pressure may lead to an auto-positive end-expiratory pressure (auto-PEEP) effect.(Crit Care Med 1996; 24:458-465)