The Science Journal of the American Association for Respiratory Care

2003 OPEN FORUM Abstracts

Accuracy of Volumes Delivered and Monitored by the Viasys Avea® Ventilator during Heliox Administration

Mark Rogers, BS, RCP, RRT1 and Charles B. Spearman, MSEd, RRT, FAARC2

1Loma Linda University Medical Center - Department of Respiratory Care. Loma Linda, CA

2Loma Linda University, School of Allied Health Professions, Department of Cardiopulmonary Sciences. Loma Linda, CA

Background: Helium-oxygen mixtures (heliox) have been advocated for the management of increased airways resistance in spontaneously breathing and mechanically ventilated patients. Past studies have demonstrated that mechanical ventilation with heliox may cause errors in delivered and displayed volumes. We sought to evaluate the volume delivery and monitoring accuracy of the Avea (Viasys Healthcare, Yorba Linda, CA), a new ventilator designed to accept heliox as an optional gas source.

Methods: Our study was designed to simulate increased airways resistance in the adult and pediatric patient. We used an Active Servo Lung (ASL5000® - IngMar Medical, Pittsburgh, PA), a digitally controlled breathing simulator and test lung. The Avea and test lung were set as follows:


Patient

Rate

Vt

PEEP

Flow

I:E Ratio

Resistance

Adult

10

1.0 L

5 cmH2O

60 LPM

1:5

20 cmH2O/L/sec

Pediatric

15

250 mL

5 cmH2O

30 LPM

1:7

50 cmH2O/L/sec


Using the supplied gas-identifying connector system, we connected 50 psig of 80/20 heliox to the compressed air inlet. For each age range, we set the ventilator to deliver an oxygen concentration of 21% (balance helium) and 40% (balance helium). For each gas mixture, a compliance of 50 and 100 mL/cmH2O for the adult settings and 20 and 40 mL/cm H2O for the pediatric settings were set to simulate the low expiratory flows commonly seen in patients with airway obstruction. We compared data collected from the exhaled tidal volume display of the Avea with data from a Collins 120 L Tissot® spirometer to determine if monitored volumes were within the error range specified by the manufacturer. We collected samples of 20 breaths for each condition. The Tissot spirometer data was corrected to BTPS.

Results: For both pediatric and adult settings, delivered tidal volumes were within the manufacturer's specification of ± (10% + 0.2 mL) of actual setting. Percent difference between Avea volume display and Tissot spirometer for each condition tested is shown in the table.

  21% O2, Balance He 40% O2, Balance He
Adult Settings 50 mL/cmH2O 100 mL/cmH2O 50 mL/cmH2O 100 mL/cmH2O
% Difference 9.3 11.8* 6.0 10.2
Peds Settings 20 mL/cmH2O 40 mL/cmH2O 20 mL/cmH2O 40 mL/cmH2O
% Difference 4.9 -0.5 8.2 -2.1


* = Outside manufacturer's specified accuracy for displayed exhaled volume: ± (10% + 20mL) of reading.

Conclusions:
Overall, during this limited study with the Viasys Avea, delivered and measured volumes were reasonably accurate although only one sample fell slightly outside (by 1%) of manufacturer's specified accuracy.

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