Efficacy of tracheal gas insufflation in acute respiratory distress syndrome with permissive hypercapnia

This study was conducted to assess the CO2-elimination efficiency of tracheal gas insufflation (TGI) in 20 patients with acute respiratory distress syndrome and to compare its efficacy during volume-controlled (VCV) and pressure-controlled ventilation (PCV). TGI was initially applied as an adjunct to VCV, with continuous flows (Vcath) of 4 and 6 L/min delivered through a catheter positioned 2 cm above the carina. Total effective tidal volume (VTeff) was held constant. The percent reductions in Pa-CO2 (%Delta Pa-CO2) were 13.3 +/- 2.1 and 16.7 +/- 2.7% at Vcath 4 and 6 L/min, respectively, which correlated well with the percent reduction in the end-tidal PCO2 from baseline (%Delta PET(CO2)) (r = 0.75, p < 0.001). An inverse relationship (r = -0.65, p < 0.001 and r = -0.59, p < 0.01 at Vcath 4 and 6 L/min, respectively) was found between the %Delta Pa-CO2 and the baseline ratio of artery to PET(CO2) difference to Pa-CO2, which was determined as the fraction of alveolar dead space (VDalv) relative to total alveolar ventilation. Twelve patients were subsequently switched to PCV combined with Vcath 6 L/min, which provided a %Delta Pa-CO2 of 16.1 +/- 3.0% (p = NS versus 17.1 +/- 2.6% during VCV). These data suggest that in patients with ARDS the change in PET(CO2) may be helpful in predicting the decrement in Pa-CO2 during TGI, and the existence of a high VDalv tends to limit its effectiveness. Further, the efficacy of TGI with VCV is equivalent to that with PCV.