The Science Journal of the American Association for Respiratory Care

2006 OPEN FORUM Abstracts

Extended System Test Performance on the Viasys Avea Ventilator with Heliox Initiation

Daria Donelly RRT, David Heitz RRT-NPS, Kevin Bullock RRT

Children's Hospital Boston and Harvard Medical School , Boston , MA

Background: The AveaTM ventilator (Viasys Healthcare, Palm Springs , CA ) is manufactured to incorporate safe heliox delivery utilizing a "smart" fitting technology.  There are two "smart" fittings, one for compressed air and the other for an 80/20 heliox mixture.  The fittings signal the ventilator which type of gas source is connected and therefore which gas controls to initiate.  Prior to patient connection an Extended System Test (EST) is recommended by the manufacturer to simultaneously determine patient circuit compliance and leak.  During the EST test the patient circuit is pressurized to 60 cmH2O for 10 seconds.  When the EST is successful, a circuit compliance factor is generated.  During volume targeted modes the volume of gas delivered is increased to include the set volume plus the volume loss as determined by the compressible volume factor.  Since the density of helium is less than that of air and oxygen we hypothesized that the compressible volume determined by an EST would be altered and should therefore be performed prior to heliox initiation.

We bench tested 3 Avea ventilators on different occasions utilizing the compressed air and heliox "smart" fitting technology.  For each of the 3 ventilators we performed an EST with the compressed air "smart" fitting and then repeated the testing with the heliox "smart" fitting connected to an H-size cylinder of an 80/20 heliox mixture.  Each EST was repeated with the FIO2 set at 1.0, 0.6 and 0.21. 

With the ventilator connected to the compressed air "smart" fitting we found no variation in each of the circuit compliance factors determined with the FIO2 set at 1.0, 0.6 and 0.21.  We did see a difference between the determined factors for each FIO2 setting with the ventilator connected to an 80/20 heliox mixture using the heliox "smart" fitting. When comparing the factors determined for each FIO2 setting between the two gas mixtures and fittings a 33% variance was seen with the FIO2 set at 1.0 and a 14% variance with an FIO2 of 0.6. There was no difference between the circuit compliances determined with the FIO2 set at 0.21(see table).

EST Circuit Compliance (mL/cmH2O)
FIO2 0.21 0.60 1.0
Heliox 2.1 2.4 2.8
Compressed Air 2.1 2.1 2.1

Conclusion: From our results an EST should not be done when transitioning from compressed air to heliox.  If it is necessary that an EST be performed during heliox utilization we recommend that it be done with the FIO2 set at 0.21.

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