2007 OPEN FORUM Abstracts
EFFECTS OF TIDAL VOLUME ON DELIVERED O2 CONCENTRATIONS WITH AN OXYGEN BLEED-IN WITH THE EMERSON COUGHASSIST MI-E DEVICE: A BENCH STUDY
J. C. Ray1, D. M. Aslin1, R. DiBlasi2, C. Hinkson1
Background: The Emerson Coughassist mechanical in-exsufflation (MI-E) device is used by patients with neuromuscular weakness and cervical spinal-cord injuries who have impaired peak cough flow. We utilize the MI-E when such patients need hyperinflation therapy and assistance with secretion removal. Many of these patients require supplemental oxygen and have artificial airways such as tracheostomy tubes. Oxygen delivery is accomplished by bleeding oxygen into the MI-E circuit during treatments. We tested the MI-E circuit with oxygen bled in to determine whether tidal volume (VT) affected the delivered oxygen fraction (FDO2)
Methods: The MI-E was connected to the Ingmar ASL 5000 test lung (IngMar Medical Ltd, Pittsburgh, PA) with an 8.0 ID tracheostomy tube and exhalation manifold. Oxygen was bled in at the device port at 15 L/min and was measured at the tracheostomy tube with a Paramagnetic O2 analyzer E-COVX gas exchange module (GE Healthcare, Chalfont St. Giles, United Kingdom). VT was varied by adjusting the peak insufflation pressure to 30, 40, and 50 cmH2O. Inspiratory time was set to 2 seconds with 2 seconds between breaths. Results are presented as mean ± standard deviation.
Results: With the test lung set to a compliance of 50 mL/cm H2O, measured VT was 1151.40 ± 0.83 mL, 1192.78 ± 1.15 mL, and 1231.40 ± 1.08 mL, respectively, for pressures of 30, 40, and 50 cmH2O. The corresponding delivered FDO2 values were 0.49 ± 0.0075, 0.46 ± 0.0022, and 0.43 ± 0.0031. With a compliance of 20 mL/cmH2O, measured VT was 625 ± 0.31mL, 830 ± 0.49 mL, and 1030 ± 0.46 mL respectively for 30, 40, and 50 cmH2O. The FDO2 was 0.92 ± 0.008, 0.55 ± 0.012, and 0.46 ± 0.005 respectively. Correlation for VT/ FDO2 relationship was r2 = 0.78, p = 0.0190. Conclusion and recommendations: Delivered oxygen concentration with MI-E varies with VT, which under the limited conditions of this study was highest with the lowest VT. Further study will be needed to understand the effects of respiratory rate, compliance, circuit design, and other variables on FDO2 during MI-E.