The Science Journal of the American Association for Respiratory Care

2000 OPEN FORUM Abstracts

PARTIAL EXPIRATORY TRACHEAL GAS INSUFFLATION (TGI) REDUCES PaCO2 WHILE SPARING TGI-AIRWAY EXPOSURE

Attwood J, McCoy R, Virag R, Bliss P. Methodist Hospital Indianapolis, IN

Background: Tracheal Gas Insufflation (TGI) has been shown to reduce minute ventilation requirements by flushing CO2 from the anatomical deadspace. Recent research has shown that a low tidal volume strategy reduces mortality in ARDS. PaCO2 control via other methods, such as TGI, may be beneficial when using this strategy. In this study, we investigated the effect of introducing TGI flow only in the latter portion of the expiratory phase, when it may be the most beneficial and have the least adverse affects.

Methods: Five normal mongrel dogs were intubated, anesthetized and ventilated to produce normal blood gas measurements, using a tidal volume of approximately 10 mL/kg (Mallinckrodt model 840 ventilator - assist control mode). When blood gas measurements had stabilized, tidal volume was reduced by approximately 45%, to produce PaCO2 measurements in the range of 70-100 mmHg. TGI was introduced approx. 1 cm above the carina at 4-8 L/min during the latter portion of exhalation using a phasic controller (Valley Inspired Products). This controller monitors the patient flow at the inlet of the tracheal tube and gates TGI flow to start when a threshold expiratory flow level is sensed and end at the onset of inspiration.

Results: Introduction of TGI flow created an average decrease in PaCO2 of 30.5 mmHg (33.9%) when compared to the values with lowered tidal volume and no TGI (P<.01 by paired t-test). TGI was applied 67.5 (± 6) % of the total expiratory time. TGI flow rate was 6.0 (± 2.0) Ipm. Mean PaCO2 results expressed as a percent change from the baseline (high tidal volume, no TGI) values are shown in the following graph:
Conclusion: Partial expiratory TGI effectively normalized PaCO2 in a reduced tidal volume strategy while sparing airway exposure to TGI. The independent controller allowed application of TGI in this selective manner. Supported by Mallinckrodt, Inc. (See Original for Figure)

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