The Science Journal of the American Association for Respiratory Care

2007 OPEN FORUM Abstracts

VOLUME ACCURACY WITH THE USE OF HELIOX IN MECHANICAL VENTILATION

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


Background: Using a mixture of helium and oxygen while mechanically ventilating patients to relieve lower airway obstruction is commonly practiced in intensive care units. The use of heliox with commercially available mechanical ventilators is usually accomplished by connecting the heliox mixture to the air inlet of the ventilator. Since most ventilators do not compensate for the difference in gas densities, particular attention to the delivered tidal volume (VT) is required. We utilized a commercially available mechanical ventilator with an internal blending system that is capable of delivering heliox instead of medical air. It identifies and compensates for the gas mixture, theoretically, enhancing stability in delivered and monitored parameters.

Methods: Intubated, sedated male domestic porcine (n=7) were ventilated with a mechanical ventilator equipped with an internal heliox blending system utilizing P A/C, PRVC, and PSV modes. Accuracy of volume delivery was assessed by comparing delivered tidal volumes measured at the patient wye using the variable orifice flow sensor (VOF) connected to the ventilator and a heated 0-35 L/min pneumotachograph that was calibrated for flow, pressure, and volume, with an .80/.20 heliox mix and .50 O2. A t-test was utilized with a p<0.05.

Results: Pigs mean weight 8.97 kg + 0.9. Mean VTE for all modes was 82 mL + 16. Mean VTE % difference + SD are shown in the table below. When comparing all modes for the .50 O2 to the heliox mix, we found that VTE % difference increased when using heliox (p<0.001).

Conclusions: This study confirms that clinicians should be vigilant in monitoring delivered tidal volumes using a commercially available ventilator equipped with an internal heliox blending system. Accuracy of delivered tidal volumes can vary greatly with the use of heliox in this system, as well as other configurations.

.50 FiO2Mean VTE % Difference +SD
PRVC 6.5 + 12.2
P A/C 5.9 + 7.7
PSV 9.2 + 11.7
.80/.20 Heliox 
PRVC 16.7 + 17.9
P A/C 20.3 + 21.1
PSV 14.3 + 12.3



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