Tracheal Gas Insufflation

The injection of a secondary flow of gas at the level of the carina during conventional mechanical ventilation has been referred to as TGI [6]. This concept was first introduced by Stresemann and Sattler [7] in 1969 who proposed TGI as an adjunct to mechanical ventilation. Ideally, this secondary gas flow is independent of the actual tidal volume (Vt) delivered by the mechanical ventilator. The role of the TGI gas flow is to flush carbon dioxide (CO2) from the anatomic deadspace of the trachea and proximal mainstem bronchi as well as the endotracheal tube and mechanical deadspace of the ventilator circuit (Fig. 1) [6]. Since CO2 only accumulates in anatomic and mechanical deadspace at end expiration, TGI flow is only necessary at end exhalation. The secondary mechanism by which CO2 elimination is enhanced, is the turbulence generated at the tip of the TGI catheter by the high velocity gas flow. This causes CO2 movement from the airways distal to the catheter tip [8].

Tgi Catheter

Fig. 1. Principles oftrachealgas insufflation (TGI). With no TGI (left) the gas in the central airways is laden with CO2 (black dots) at end expiration. This gas is then rebreathed into the alveoli at the onset ofthe next inspiration. With TGI (right), the gas in the central airways is replaced with fresh gas during expiration, and less CO2 is rebreathed during the next inspiration, effectively lowering the deadspace. From [6] with permission.

Fig. 1. Principles oftrachealgas insufflation (TGI). With no TGI (left) the gas in the central airways is laden with CO2 (black dots) at end expiration. This gas is then rebreathed into the alveoli at the onset ofthe next inspiration. With TGI (right), the gas in the central airways is replaced with fresh gas during expiration, and less CO2 is rebreathed during the next inspiration, effectively lowering the deadspace. From [6] with permission.

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