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[The effects of auto-triggering on patient-ventilator interaction in noninvasive mechanical ventilation during air leak].

OBJECTIVE
To study the relationship between air leak and auto-triggering in noninvasive positive pressure ventilation (NIPPV), and the effects of auto-triggering on patient-ventilators interaction.


METHODS
Five different types of noninvasive ventilators, a lung simulator and 14 healthy volunteers were studied by using a quantificational air leak model and a spirometer which monitoring the pressure, flow and volume curve in the tube continuously. SPSS version 10.0 was used for statistical analysis. Data were presented as x +/- s, and means were compared with analysis of variance.


RESULTS
In the study of lung simulator, the percentage of times of auto triggering in total testing times was from 24% -90% in the BiPAP mode in various ventilators. Air leaking capacity was the most crucial factor related to auto triggering (beta = 0.709, OR = 2.032). With increased air leak level, 14 volunteers all presented with auto triggering. All the volunteers' respiratory rate increased and tidal volume decreased with the increasing level of air leak.


CONCLUSION
Auto-triggering occurred when air leak increased in NIPPV. The insufficient compensation of flow base line may be the cause for auto-triggering. Auto-triggering can impair patients ventilation.