The Science Journal of the American Association for Respiratory Care

2004 OPEN FORUM Abstracts

Providing Oxygen Therapy During Exhaled Breath Condensate Collection Using the RTube™

Brian K. Walsh, RRT-NPS, RPFT; John Vaughan; John Hunt, MD. University of Virginia Pediatric Respiratory Medicine; Charlottesville, Virginia

Background: Measurement of biomarkers in exhaled breath condensate (EBC) provides a new non-invasive research tool to study airway chemistry and inflammation in lung disease. These assays have potential clinical utility in patient management. The RTube™ is a single patient use disposable EBC collection device through which a patient orally breathes, utilizing 2 one way valves that allow room air to be inhaled while directing all exhaled airflow through a 9 inch polypropylene collection chamber cooled by an aluminum sleeve. This process condenses the aqueous components of exhaled breath, as well as enlarging and trapping particles that are evolved by turbulent flow from the airway lining fluid. This very safe system is highly applicable to non-invasive collection of exhaled breath constituents even in patients with marked pulmonary insufficiency, and we therefore have undertaken to expand its utility by developing simple means to provide supplemental oxygen during the 3-10 minutes that it takes to collect EBC.

Methods: An oxygen adapter and 6 inch corrugated tubing were connected to the inspiratory valve of the RTube™. The oxygen adapter was placed proximal to the inspiratory valve which allows the 6 inches of corrugated tubing to become a 50 ml oxygen reservoir. Starting flows were calculated using a low flow FIO2 estimating equation:

FIO2 (estimated) = O2 + 0.21 (V insp – O2)

(V insp)

Three levels of spontaneous minute ventilation (MV) by one healthy volunteer were used to test the equation and oxygen delivery set-up. A FIO2 of .35 was targeted to be delivered. Minute ventilations of 12, 8, and 3 liters per minute were chosen and measured by a Wright Respirometer. Average inspiratory flows were calculated by multiplying the subject’s minute ventilation by the sum of the observed I:E ratio. FIO2 was analyzed proximal to the mouth piece using a MSA Miniox oxygen analyzer.

Results:

MV target (l/min) FIO2 target Observed I:E ratio Measure MV Oxygen flow added to new RTube™ Reservoir (L/min) Calculated inspiratory flow (L/min) Average Measured FIO2
12 .35 1:2 12.6 6.5 36 .36
8 .35 1:2 7.8 4.2 24 .38
3 .35 1:2 3.6 1.8 9 .39

Conclusion: Oxygen therapy can be successful provided during RTube sampling by simply attaching oxygen with a small reservoir to the inspiratory limb of the device. As with all low flow oxygen devices FIO2 is variable depending on the patients inspiratory flow and oxygen applied to the device. Our results show a higher measured FIO2 than targeted FIO2 at lower inspiratory flow due to the constant reservoir size. Simple monitoring with a pulse oximeter would allow the clinicians to titrate the oxygen flow to the desired oxygen delivery during sampling. Precise oxygen titration can also be provided by changing the length of the reservoir tubing.

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