In the setting of acute lung injury, ventilatory strategies that adjust minute ventilation (VE) to achieve eucapnia often lead to alveolar rupture or damage. Tracheal gas insufflation (TGI) reduces the VE requirements of conventional mechanical ventilation by decreasing the effective dead-space fraction (VD/VT) of each breath. We studied the effect of catheter flow rate (Vcath) and position as well as catheter tip diameter and configuration on CO2 elimination during TGI-augmented pressure-controlled ventilation (PCV) in normal dogs. We studied three catheter positions (1, 5, and 10 cm above the carina) at Vcath of 2, 5, and 10 L/min (n = 6). When the catheter tip was positioned 1 cm above the carina, PaCO2 decreased significantly from a baseline (PCV alone) of 67 +/- 10 mm Hg to 52 +/- 11, 43 +/- 9, and 32 +/- 7 mm Hg (p < 0.05) at Vcath of 2, 5, and 10 L/min, respectively. For the same Vcath values, positioning the catheter tip 10 cm above the carina increased PaCO2 to 54 +/- 15, 46 +/- 12, and 40 +/- 11 mm Hg. Advancing the catheter tip 2 cm below the carina did not improve PaCO2 significantly (n = 3). At a catheter position of 1 cm above the carina and a Vcath of 10 L/min, changing the luminal inner diameter (1.5 versus 3.0 mm) or tip configuration (open tip versus occluded tip with two side holes) of the catheter did not change PaCO2.(ABSTRACT TRUNCATED AT 250 WORDS)