The Science Journal of the American Association for Respiratory Care

2011 OPEN FORUM Abstracts

EFFECT OF A HIGH FREQUENCY AMPLITUDE ATTENUATION DEVICE ON EXHALED FLOW VARIABILITY DURING HIGH FREQUENCY OSCILLATORY VENTILATION.

Craig D. Smallwood, John Thompson; Respiratory Care, Children's Hospital Boston, Boston, MA

BACKGROUND: Due to a sinusoidal flow pattern and high rate of breath delivery during high frequency oscillatory ventilation (HFOV), it is technically difficult to accurately assess the exhaled gas flow using conventional airway monitors. Accurate exhaled gas analysis is necessary for indirect calorimetry and volumetric capnography. The purpose of this study was to demonstrate the effects of the high frequency amplitude attenuation device (HAAD) on the measured exhaled gas flow variation during HFOV. METHODS: The HAAD forms a seal around the exhalation valve of the HFOV device and incorporates an anesthesia bag (A-bag), to which an airway monitor is tethered via a standard connector. The HAAD directs exhaled gas from the HFOV device through the A-bag which then vents to an airway monitor for analysis. A bench model was constructed to test the device. The Sensormedics 3100A was connected to a test lung. The HAAD was attached to the exhalation port of the ventilator circuit. A flow analyzer, the eVent PF300, was used to measure flow rates. Data was recorded using a laptop computer and Flowlab Flow-Analyzer software during ventilation using an unmodified control circuit (without the HAAD) and a modified circuit (with the HAAD). Furthermore, recordings were made with the additional attachment of 1 (HAAD+1) and 2 (HAAD+2) 1L A-bags in series to the HAAD. The data was imported into MS Excel and GraphPad Prism for analysis. Maximum, minimum, range and standard deviation (SD) of flow were calculated to compare the variation of measured flow with and without the HAAD. RESULTS: Figure 1 illustrates the variation in measured flow with and without the HAAD. Results from the experiment are found in Table 1. CONCLUSIONS: The application of the HAAD reduced the flow range and standard deviation considerably. Although the application of additional A-bags to the HAAD did continue to reduce the range and standard deviation of flow, the degree to which they did so was minimal. The integration of the HAAD with an airway monitor may enable enhanced gas analysis during HFOV such as volumetric capnography and indirect calorimetry.
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