The Science Journal of the American Association for Respiratory Care

2007 OPEN FORUM Abstracts

EVALUATION OF ACCURACY OF DISPLAYED TIDAL VOLUME WITH THREE AIRWAY SENSORS IN AN ANIMAL MODEL

M. J. Heulitt1, 2, S. J. Holt2, T. L. Thurman2, A. E. Gibbs2

Background: Optimal mechanical ventilation in infants and pediatrics depends on reliability of flow sensors to correctly measure flow and integrate it into accurately displayed delivered tidal volumes. However, reliability of these devices has not been established. We hypothesize that reliability would be affected by both the type of flow sensors and ventilator controllers utilized.

Methods: Intubated, sedated Sprague Dawley rats (n=14) were ventilated with both control and support ventilator modes utilizing two different ventilators, one ventilator using a fixed orifice flow sensor (FOF), and the other ventilator utilizing a hot wire flow sensor (HWF), and a variable orifice flow sensor (VOF), independently. Accuracy of delivered tidal volume was obtained by comparing the displayed volume of the different sensors from each ventilator to breath waveforms acquired using a heated 0-5 L/min pneumotachograph calibrated for flow, pressure, and volume. Analysis was performed utilizing ANOVA with p<0.05.

Results: Rats mean weight was 472g + 46. For all modes, mean VTE % difference + SD are shown in the table below. For VCV and PCV (TCPL A/C), there was a difference between all three sensors. For PSV there was a difference with the HWF only. R-square values for the FOF 0.80, HWF 0.54, and VOF 0.16.

Conclusions: Our conclusions are that the accuracy of delivered VTE is affected by both the flow sensor and ventilator controller to deliver the breath. We speculate that the flow sensor and the ventilator controller are associated with varying degrees of flow accuracy and control. We would expect volume accuracy for all modes to be equal if the flow accuracy were related to the inaccuracy of the flow sensors only.

Mean VTE % Difference + SD
Mode FOF Mode HWF VOF
VCV *18.8 + 12.7 V A/C *-0.8 + 8.9 *37.9 + 35.6
PCV †6.1 + 10.2 TCPL A/C †-3.2 + 9.3 †41.8 + 34.7
PSV 11.8 + 11.1 PSV ‡-7.1 + 8.2 11.3 + 32.0

* p<0.001
† p<0.001
‡ p<0.001

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