The Science Journal of the American Association for Respiratory Care

1999 OPEN FORUM Abstracts

HELIUM DELIVERY BY BIPAP

Sunisa Chatmongkolchart, MD, Purris Williams, BA, RRT, Ray Ritz, BA, RRT, Robert M Kacmarek, PhD, RRT, FAARC, Dean Hess, PhD, RRT, FAARC. Departments of Anesthesia and Critical Care, and Respiratory Care, Massachusetts General Hospital; Harvard Medical School; Boston, MA.

Noninvasive positive pressure ventilation (NPPV) is used increasingly to avoid intubation during acute respiratory failure. Heliox is occasionally used for acute asthma. It has been speculated that NPPV with heliox may be useful in the management of acute asthma, and some clinicians have used this combination. We used a bench model to evaluate the delivery of heliox with BiPAPÒ. Method: A BiPAPÒ S/T-D30 ventilator (Respironics, Murrysville, PA) set to timed mode (30% inspiratory time) with plateau exhalation valve (Respironics, Murrysville, PA) was connected to a Michigan Instruments TTLÒ (Michigan Instruments, Inc. Grand Rapids, MI), compliance 0.05 L/cm H2O. Inspiratory/expiratory pressure settings (cm H2O) were 10/0, 10/5, 15/5, 20/5 and 20/10. Respiratory rates of 15/min and 30/min were used. A heliox mixture (80% helium/20% oxygen) was added either proximal (near the lung model) or distal (near the ventilator) at flows of 0, 5.4, 10.8, or 18 L/min using an oxygen flowmeter (Timeter Instrument Corp., St.Louis, MO) set at 0, 3, 6, or 10 L/min. Oxygen flows (Precision Medical, Inc. Northhampton, PA) of 0, 5, and 10 L/min were added in the proximal or distal position. After 10 minutes at each combination of settings, helium concentration in the lung model bellows was measured with a calibrated helium analyzer (PK Morgan LTD, Kent, England). Pressure in the lung model was measured with a calibrated pressure transducer (Validyne, Northridge, CA), digitized (Dataq Instruments, Inc. Akron, Ohio), and continuously recorded.

Results: Delivered helium concentration was not affected by respiratory rate (P=0.46), proximal or distal heliox infusion (P=0.64), or oxygen infusion (P=0.94). Helium concentration in the lung model was significantly affected by helium flow (P<0.001) and BiPAPÒ setting (P=0.01). See Table for helium concentrations at the combinations of BiPAPÒ settings and heliox flows. There was no combination of settings in which the delivered helium concentration exceeded 60%. There was no significant effect of heliox on inspiratory pressure (P>0.5) or expiratory pressure (P>0.3). Conclusion: The addition of heliox to the BiPAPÒ circuit did not affect the function of the ventilator as reflected in the inspiratory and expiratory pressure settings. However, very high heliox flows (18 L/min) only resulted in delivery of helium concentrations approaching 60%. This suggests that use of BiPAPÒ for heliox therapy may be marginally effective. These results should be confirmed clinically.

BiPAPÒ Heliox Flow (L/min)
setting 5.4 10.8 18
20/5 0.12±0.02 0.24±0.04 0.40±0.06
20/10 0.14±0.02 0.29±0.04 0.48±0.07
15/5 0.15±0.02 0.28±0.03 0.46±0.08
10/0 0.17±0.04 0.31±0.02 0.50±0.06
10/5 0.22±0.10 0.37±0.09 0.52±0.05

OF-99-081

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