The Science Journal of the American Association for Respiratory Care

2007 OPEN FORUM Abstracts

EFFECT OF TUBE COMPENSATION ON ALVEOLAR PRESSURE IN DIFFERENT INSPIRATORY FLOW IN A LUNG MODEL STUDY

K. Hayashi1, Y. Kawano1, K. Horiuchi1


Background: Tube compensation (TC) reduces work of breathing imposed by high PEEP. As support pressure of TC is calculated with the measured flow, alveolar pressure might elevate in case the calculated pressure overcompensates when patient’s inspiratory effort is greater. Although TC level (%) is adjustable, the rationale has not been fully investigated. The purpose of this study is to assess whether lung compliance or resistance is associated with overcompensation.

Methods: In the test lung model (TTL, Michigan Instruments, MI), lung compliance and resistance were set to 20 or 50 ml/cmH2O, and 5 or 20 cmH2O/L/sec, respectively. Puritan Bennett 840 ventilator was connected to TTL via an artificial trachea intubated with an 8.0mm cuffed endotracheal tube, and set to 25cmH2O of CPAP with TC of 100%. Circuit and bellows pressure in inspiratory flow of 20, 40, 60, and 80L/min were measured by PTS2000 (Nellcor Puritan Bennett).

Results: Circuit pressure rose as inspiratory flow increased in all condition. At higher resistance bellows pressure was maintained around CPAP level, whereas it rose in proportion to flow increase at lower resistance. Decreasing TC level ameliorated the elevation of bellows pressure. Changes in compliance had little effect on bellows pressure in the current study setting.

Conclusions: The findings of the current study suggested that the level of compensation should be appropriately adjusted to avoid unexpected increase in alveolar pressure in patients with lower resistance and increased inspiratory effort.

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