Tracheal Gas Insufflation during Pressure-control Ventilation: Effect of Catheter Position, Diameter, and Flow Rate

In the setting of acute lung injury, ventilatory strategies that adjust minute ventilation ( e) to achieve eucapnia often lead to alveolar rupture or damage. Tracheal gas insufflation (TGI) reduces the e 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 (cath) 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 cath 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 cath of 2, 5, and 10 L/min, respectively. For the same cath 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 cath 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. Mean airway opening pressure and airway opening pressure at the initiation of inspiratory flow increased slightly during TGI-augmented PCV, suggesting that TGI increased end-expiratory lung volume. Our data confirm that TGI can effectively augment alveolar ventilation during PCV. This effect depended strongly on cath; catheter tip position was not crucial, so long as it was placed within a few centimeters of the main carina.