The Science Journal of the American Association for Respiratory Care

2007 OPEN FORUM Abstracts

PREDICTION OF INSPIRED HELIUM CONCENTRATION IN LARGE VOLUME MEDICATION NEBULIZERS (LVMN).

M. McPeck1


Background: FIHe <60% has been identified by some investigators as too low to be clinically useful. Most LVMNs rely on the principle of an O2-driven jet nebulizer to produce aerosol. For HeO2 therapy, HeO2 is metered into the device adjacent to, or distal to, the nebulizer jet to render a therapeutic mixture. The Healthline Medicator® Möbius™ is a continuous aerosol drug delivery system using a tiny gas mixing chamber for mixing O2 + 80/20 HeO2 proximal to the nebulizer jet with a total combined flow of 8 L/min. An integral reservoir bag compensates for any loss of efficiency caused by powering the nebulizer with HeO2. STUDY QUESTIONS: (1) Do conventional jet-driven LVMNs attain a useful level of FIHe, and (2) how does the Möbius compare against conventional LVMNs?

Methods:
I conducted a spreadsheet analysis comparing Möbius with conventional LVMNs Airlife “Misty Finity” (MF) and DHD “Flo-Mist” (FM). Using manufacturer’s package inserts to provide recommended flowrates, the achievable FIHe for all devices was calculated from the following equations:
FIO2 = (O2 Flow x 1.0) + (HeO2 Flow x 0.2 or 0.3) / Total Flow and FIHe = 1.0 – FIO2.

Results:
Based on this standard equation, the Möbius is predicted to achieve an FIHE of 80, 70 or 60% with 80/20 HeO2 flowrates of 8, 7 or 6 L/min respectively. In contrast, the FM only achieves FIHe of 50% with 22 L/min of 80/20 or 32 L/min of 70/30 HeO2, and requires an impractical flowrate of 90 L/min of 80/20 to reach a FIHe of 70%. However, the FM can not achieve FIHe of 80% with 80/20 or FIHe of 70% with 70/30. Similarly, the MF can achieve FIHe of 80% with 18 L/min of 80/20 HeO2. However, it too requires an impractical flowrate of 80 L/min of 80/20 to achieve a FIHe of 70%. The MF can not reach FIHe of 80% with secondary flow of 80/20 or 70% with a secondary flow of 70/30.

Conclusion: Package inserts indicate typical LVMNs are designed to deliver FIHe ~50%; the gas mixing equation verifies that they can not achieve high (70-80%) FIHe with practical secondary gas flows. Mathematically, it is shown that impractically high flowrates of HeO2 ranging from 760-1,030 L/min are required for 70-80% FIHe delivery with the MF and FM. High consumption of HeO2 is wasteful, expensive and labor-inefficient due to frequent cylinder changes. Conversely, the Möbius, by virtue of gas mixing proximal to the nebulizer jet, is predicted to achieve a clinically useful range of FIHe from 60–80% using no more than 8 L/min of 80/20 HeO2.

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