The Science Journal of the American Association for Respiratory Care

1998 OPEN FORUM Abstracts

DEMAND OXYGEN DEVICES: TISSUE OXYGENATION IN THE CONTEXT OF CONSERVATION

George G. Burton, MD, Wright State University/Kettering Medical Center, Kettering, Ohio, Diannah Henderson, RN, Kettering Medical Center, Kettering, Ohio, Sallee Harrington, CRTT, Kettering Medical Center, Kettering, Ohio

Continuous flow oxygen administration (CFO_{2}) is the reference standard for evaluation of demand oxygen delivery devices. CFO_{2} is effective because it is available throughout the respiratory cycle. Current demand oxygen devices deliver burst doses of oxygen during inspiration only, and are marketed using terms such as "flow-equivalence" and "savings-ratio" when comparing themselves to CFO_{2}. We have observed that these devices may fail to oxygenate patients adequately, particularly during exercise, and we suspect that there may be an optimal "window" in the respiratory cycle in which burst oxygen will maintain alveolar PO_{2} and oxygen uptake. This "window" probably occurs during early inspiration, and enrichment of FIO_{2} then should result in improved oxygenation. We assessed peripheral oxygen saturation (SpO_{2}) during rest and exercise in stable oxygen-dependent COPD patients. We evaluated three commercially available oxygen conserving devices and a demand oxygen conservation device (DOCD) currently under development. Patients' ability to maintain a "safe" SpO_{2} (92% was determined and the results expressed as a surrogate for oxygen consumption using a "mileage" analog (ft-kg/L of supplemental O_{2} consumption). A custom data acquisition device was used to identify the triggering of each demand device in relation to events in the respiratory cycle. The amount of oxygen delivered per breath was determined by calculating the output flow and flow duration of each device. The study was unblinded; order of device testing was randomized. Four devices were tested: DeVilbiss Pulse-Dose; Nellcor Puritan-Bennett CR-50; Chad Therapeutic Oxymatic; and the DOCD prototype. Results: The devices studied required 40-68% of the oxygen flow requirements of the CFO_{2} "gold standard". Only the DOCD device permitted more "safe" work output than CFO_{2}. The other devices permitted 66-79% of the work output allowed by CFO_{2}. However, DOCD allowed a surprising 63% more work output than CFO_{2}. Conclusion: (1) Tissue oxygenation during exercise is more important than oxygen savings alone. This is true since O_{2} conservers are designed for ambulatory patients who need supplemental O_{2} to maintain an active lifestyle. (2) O_{2} conservers that deliver substantial O_{2} savings but which fail to increase the patient's exercise tolerance do not achieve the intended effect of increasing mobility while insuring patient safety. (3) Devices that trigger oxygen flow after the onset of inhalation may not meet the "window" for optimum tissue oxygenation.

The 44th International Respiratory Congress Abstracts-On-DiskĀ®, November 7 - 10, 1998, Atlanta, Georgia.

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