Catheters for tracheal gas insufflation

As an adjunct to mechanical ventilation, tracheal gas insufflation (TGI) injects gas flow into the trachea to flush carbon dioxide (CO2) from the anatomical and mechanical dead space, but the addition of TGI flow from a catheter may cause problems related to increased flow velocity at the catheter tip. Forward momentum and turbulence beyond the tip oppose expiratory flow and may cause or increase intrinsic positive end-expiratory pressure. If the catheter is placed within the endotracheal tube (ETT), the catheter itself acts as a resistive element to exhalation. Effects of the catheter presence (contact on or whipping against the airway) or local rapid gas flow effects on the tracheal mucosa are possible. Thus far, TGI has been delivered through a range of catheter sizes and styles. Two general design modifications have been incorporated in TGI systems to address the possible problems: embedding the catheter flow channel within the ETT, and directing the TGI flow cephalad. The LaBrune-Boussignac tube was designed with 6 or 8 channels embedded within the ETT, from which TGI flow exits laterally within the ETT at 1.5 cm from its tip. This avoids the use of a catheter and thus avoids local traumatic effects. A reverse-thrust catheter has been designed to direct flow within a sheath around the catheter tip; flow exits cephalad from a gap between the sheath and the catheter shaft. As part of a proposed ventilatory mode (intratracheal pulmonary ventilation) the reverse-thrust catheter delivers the tidal breath and, additionally, flushes CO2 and accelerates secretion removal during exhalation. A reverse-flow design ETT has been developed with two channels, one for tidal volume delivery and the other for TGI flow. The TGI channel is relatively large and flow is directed cephalad by a nozzle at the catheter tip. A recently developed bidirectional catheter allows the option of delivering TGI flow cephalad, towards the lungs or in both directions. Unfortunately, to be convenient, the use of specially designed catheters or ETTs requires the anticipation of TGI use. A complete system for the safe and convenient use of TGI in ventilated patients is not as yet available, but concerns about the safety and convenience of TGI delivery have been addressed with recent advances in catheter/tube design.