The Science Journal of the American Association for Respiratory Care

2005 OPEN FORUM Abstracts

BENCH TEST EVALUATION OF A GAS CONSERVATION DEVICE VERSUS STANDARD FREE FLOW DELIVERY OF HELIOX

Michael Tracy BS, RRT-NPS, Timothy R. Myers BS, RRT-NPS. Department of Pediatrics Rainbow Babies & Children's Hospital, Case University, Cleveland, OH

BACKGROUND: Heliox, because of its lower gas density and potential to promote laminar gas flow, is frequently an adjunctive intervention for the treatment/support of obstructive airflow in a wide age range of patients. The purpose of this bench study was to evaluate the Aptaér heliox delivery system (GE Medical, Madison, WI) to conserve heliox compared to the traditional free-flow delivery of heliox via flow meter for non-intubated patients.

METHODS:
Eight H-cylinders of heliox from the same lot were obtained from AGA/ Linde Gas Co. (Cleveland, OH). Baseline data for the free-flow delivery of heliox from an H-cylinder was collected by measuring the heliox consumption (psig/minute and psig/hour) from a calibrated air flow meter from 2 separate h-cylinders with starting psig of 2100. A calibrated flow meter was set at 9.5 L/M (density correction factor=1.56) to deliver the equivalent of 15 L/M of flow. Gas consumption was measured serially every hour and averaged. To collect gas consumption data for the inspiratory-triggered Aptaér, a Dräger Evita 4 (Drager, Telford, PA) was connected to the inlet port of an IngMar PMG 3000 test lung (IngMar Medical, Pittsburg, PA). The right-side bellows was slaved to the left-side bellows to create a negative pressure to trigger the Aptaér. The IngMar compliance was set at 40 ml/cm H2O, resistance for each bellows was set at 10 cm H2O/L/s, and bellows and endotracheal tube leaks were set at zero. The Aptaér circuit patient wye was connected to the right side output port of the test lung. The Aptaér and Dräger Evita 4 were calibrated according to the manufacturer's guidelines before connection to the test lung. Aptaér was set at the following settings: Pressure support = 10 cmH2O, Inspiratory Trigger = -0.3 cmH2O, Inspiratory Rise = 5, End flow = 40% and nebulizer = off. The ventilator was sequentially set to deliver four different minute volumes (MV) (2.5, 5.0, 7.5 and 10 L (all ± 10%)) with SIMV. Other ventilator settings were O cmH2O PEEP, O cmH2O pressure support, Ramp = 1.0, Ti = 1.0 to 1.5 seconds and FIO2 =0.21. We selected clinically appropriate rates and tidal volumes for patients with airflow obstruction to achieve the four minute ventilations desired. Gas consumption (psig/minute and psig/hr) was serially recorded every hour at each of the four MV and averaged.

RESULTS:
All cylinders were equilibrated to 71 degrees Fahrenheit prior to use in the study. The average cost of heliox at our institution is $43.66 per cylinder and we average approximately 250 h-cylinders of heliox per year. Data on gas consumption and 24-hour cost of gas is listed by delivery method and minute ventilation (where applicable) and is summarized in the table below:

Delivery Device Minute Ventilation Psig /minute Psig /hour Cylinders / 24 hours 24-hour Cost of Gas
Free-flow delivery of heliox via calibrated air flowmeter N/A 5.4 321.8 3.7 $160.56
Aptaér Delivery System 2.5 2.0 121.6 1.4 $60.69
Aptaér Delivery System 5.0 2.7 163.0 1.9 $81.31
Aptaér Delivery System 7.5 2.6 158.3 1.8 $79.00
Aptaér Delivery System 10.0 3.9 236.3 2.7 $117.88

CONCLUSION: In this bench test based on clinically appropriate minute ventilation for airflow obstructed patients, the Aptaér device for the delivery of heliox decrease gas waste between 27-63% based on minute ventilation. The estimated financial impact at our institution is between $2,500 and $6,875 per year.

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