Chest
Laboratory and Animal InvestigationsEffects of Gas Leak on Triggering Function, Humidification, and Inspiratory Oxygen Fraction During Noninvasive Positive Airway Pressure Ventilation
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Lung Model and Ventilators
We used a custom-made bellows-in-a-box model lung12 to simulate spontaneous breathing (Fig 1). The lung consisted of two lung compartments within a rigid box. The space around the compartments simulated the pleural space. The diaphragm compartment bellows was connected to a T-tube through which gas flow was injected to create a Venturi-establishing negative pleural pressure resulting in inspiration of the lung bellows. The source gas was connected to a custom-made pressure regulator and a
Triggering Evaluation
Table 1shows DT and PI for each leak level on all ventilators. The Puritan-Bennett 7200ae and Puritan-Bennett 840 showed uncontrollable self-triggering when the gas leak was > 18 L/min at end-expiration. The BiPAP Vision and BiPAP S/T-D adequately compensated for all leaks, and PI and DT were not affected by any air leak (Fig 3,top,A, andbottom,B;Table 1), nor by either airway resistance (only data for 5 cm H2O/L/s are presented inTable 1).
Fio2Evaluation
Figure 4shows representative waveforms for Fio2and
DISCUSSION
Major findings of this study are that bilevel pressure ventilators could adequately compensate for all levels of leak evaluated, while ICU ventilators were not able to cope with large leaks. As the leak increased, the bilevel ventilation inspiratory triggering response was not affected. The Fio2delivered by the BiPAP S/T-D was affected in ways not predicted by the formula when the gas leak was large. The MR290 was able to maintain temperature and humidity under all leak conditions.
NPPV is
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