Effects of Tracheal Gas Insufflation and Tracheal Gas Exsufflation on Intrinsic Positive End-Expiratory Pressure and Carbon Dioxide Elimination

Abstract

Background

Tracheal gas insufflation (TGI) reduces arterial carbon dioxide tension (Paco₂) when used in conjunction with mechanical ventilation, but antegrade TGI flow increases intrinsic positive end-expiratory pressure (auto-PEEP) or end-expiratory lung volume (EELV). Tracheal gas exsufflation (TGE) might reduce TGI-elevated EELV while retaining the CO2 elimination effects of TGI.

Methods

An apparatus was designed to control TGI and/or TGE during selected portions of expiration. The first phase of the study examined the general effects of expiratory TGI and TGE on EELV and CO2 elimination in a mechanical test lung. In the second phase, effects on normal physiology were tested in uninjured dogs. Changes in EELV were measured by respiratory induc-tance plethysmography, and Paco, was continuously monitored. TGI and TGE were applied sep-arately and in combination during all or half of the expiratory phase. TGI/TGE combinations found to be most effective at CO₂ elimination in the test lung model were applied in the animal tests.

Results

TGI raised EELV and TGE lowered EELV in both models, and exerted their greatest effects on EELV in the latter half of expiration. In the animal model, the TGI/TGE interventions tested reduced Paco, by 16-32% (p < 0.01) compared to baseline Paco, similar to or greater than reported clinical studies.

Conclusions

Combining TGI and TGE allowed precise control of EELV in both models. Second-half TGI provided the most effective CO₂ elimination. [Respir Care 1999;44(8):918-924] Key words: tracheal gas exsufflation, tracheal gas insufflation, auto-PEEP, CO, elimination, lung model.