TRACHEAL GAS INSUFFLATION COMBINED WITH HIGH-FREQUENCY OSCILLATORY VENTILATION

Objectives: To determine the efficacy of tracheal gas insufflation del ivered by two different catheter designs on CO2 elimination when used in conjunction with high-frequency oscillatory ventilation. Design: A nonrandomized before and after trial. Each animal served as his own co ntrol. Subjects: Ten mongrel dogs weighing 20.9 +/- 1.9 kg. Four anima ls were assigned to a normal lung group and six animals underwent lung injury by large volume saline lavage. Intervention: Permissive hyperc apnia was allowed to occur by selecting oscillator settings that would lead to alveolar hypoventilation. Proximal mean airway pressure was k ept constant. Tracheal gas was insufflated at 1 cm above the carina fo r 30-min periods at gas flows of 5 to 15 L/min. Measurements and Main Results: Carinal pressure, hemodynamic parameters (cardiac output, mea n arterial pressure, pulmonary arterial pressure, pulmonary artery occ lusion pressure), and gas exchange parameters (PacO(2), PaO2, PaO2/FIO 2, shunt fraction, DO2) were measured. For the normal dogs, at cathete r flow of 15 L/min, the forward thrust catheter increased carinal pres sure and PaO2/FIO2 by 30% (p < .003) and 105% (p < .005), respectively . The forward thrust catheter reduced PacO(2) by 40% (p < .04). The re verse thrust catheter increased PaO2/FIO2 by 102% (p < .001) and decre ased carinal pressure and PacO(2) by 44% (p < .001) and 34% (p < .003) , respectively. For the injured dogs, at catheter flow rate of 15 L/mi n, the forward thrust catheter increased carinal pressure, PaO2, and P aO2/FIO2 by 6% (p < .001), 23% (p < .001) and 24% (p < .02), respectiv ely. The forward thrust catheter reduced PacO(2) by 29% (p < .002). Th e reverse thrust catheter increased PaO2 and PaO2/FIO2 both by 11% (p < .02) and reduced carinal pressure and PacO(2) by 23% (p < .001) acid 18% (p < .002), respectively. Conclusions: Tracheal gas insufflation is capable of improving oxygenation and ventilation in acute lung inju ry when combined with high frequency oscillatory ventilation. The addi tion of this second gas flow at the level of the carina raises or lowe rs 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 dis tal airway pressure; lowering distal airway pressure may lead to atele ctasis, whereas raising distal airway pressure may lead to an auto-pos itive end-expiratory pressure (auto-PEEP) effect.