The Science Journal of the American Association for Respiratory Care

2005 OPEN FORUM Abstracts

TRIGGER RELIABILITY IN PORTABLE VENTILATORS

Richard Branson MSc RRT FAARC, Jay Johannigman MD. University of Cincinnati, Cincinnati, OH 45255

INTRODUCTION: Ventilators are often evaluated using work of breathing. These values allow comparisons, but the values in joules/L are difficult to translate into clinical differences. We propose the testing of trigger reliability. Trigger reliability is the appropriate response to an effort without auto-triggering (triggering in the absence of effort) or missed triggers (failure to trigger in face of an effort).

METHODS: We used a lung simulator (ASL 5000, Ingmar medical) to test seven portable ventilators (Drager Savina, Hamilton Raphael, Newport HT-50, Pulmonetic Systems LTV-1000 and LTV 800, Versamed iVent, Viasys Vela). A scheme of 26 breaths with 4 breath periods of no effort was created. The first breath was the greatest in magnitude followed by 7 progressively smaller breaths, then two breath periods with no effort followed by a group of 18 breaths from weakest to strongest and back again. This period was followed by 2 breath periods with no effort. The efforts resulted in a negative pressure of 0.2 cm H2O up to negative 2.0 cm H20 with inspired volumes of 10 to 110 mL. We evaluated each ventilator at the lowest trigger setting and then at a setting where auto-triggering was > /= 2 per time period. For each simulated breath confirmation of ventilator triggering was made by changes in volume and flow signals. Each ventilator was tested at 0 and 5 cm H2O PEEP.

RESULTS: Ventilators demonstrated important differences in the ability to trigger at small efforts and in preventing auto-triggering. Table 1 displays the number of missed and auto-triggers at the lowest flow or pressure trigger sensitivity setting. Total number of triggers was 26 with 4 breath periods of no effort.

  Missed Triggers Auto-Triggers Lowest effort detected (cm H2O)
Savina 4 0 - 0.6
Raphael 3 0 -0.6
HT-50 4 5 -0.8
LTV-1000 2 1 -0.4
LTV-800 5 0 -0.8
iVent 3 6 -0.6
Vela 3 4 -0.8

After adjusting sensitivity to reduce auto-triggers to < /=2 per trial , missed triggers increased and the lowest effort detected was increased significantly. Table 2 depicts this data.

  Missed Triggers Auto-Triggers Lowest effort detected (cm H2O)
Savina 4 0 - 0.6
Raphael 3 0 -0.6
HT-50 7 1 -1.3*
LTV-1000 2 1 -0.4
LTV-800 4 0 -1.1*
iVent 6 2 -1.3*
Vela 5 2 -1.1*

* p< 0.05 compared to same ventilator at lowest sensitivity setting.

PEEP did not affect trigger reliability.

DISCUSSION: Trigger reliability is a unique method of evaluating ventilator performance which can detect differences in the ability of the ventilator to trigger appropriately and avoid auto-triggering. At the most sensitive settings, many ventilators auto-trigger in order to be able to sense small trigger efforts.

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